document_title: Language development

question_text: aspect /component of language that includes the structure and rules of language

question_tokens: aspect / component of language that includes the structure and rules of language

text: Language development

text: Theoretical frameworks[edit]

text: Language development is thought to proceed by ordinary processes of learning in which children acquire the forms, meanings, and uses of words and utterances from the linguistic input.[citation needed] The method in which we develop language skills is universal; however, the major debate is how the rules of syntax are acquired.[citation needed] There are two major approaches to syntactic development, an empiricist account by which children learn all syntactic rules from the linguistic input, and a nativist approach by which some principles of syntax are innate and are transmitted through the human genome.[citation needed]

text: The nativist theory, proposed by Noam Chomsky, argues that language is a unique human accomplishment, and can be attributed to either "millions of years of evolution" or to "principles of neural organization that may be even more deeply grounded in physical law".[3] Chomsky says that all children have what is called an innate language acquisition device (LAD). Theoretically, the LAD is an area of the brain that has a set of universal syntactic rules for all languages. This device provides children with the ability to make sense of knowledge and construct novel sentences with minimal external input and little experience. Chomsky's claim is based upon the view that what children hear—their linguistic input—is insufficient to explain how they come to learn language.[citation needed] He argues that linguistic input from the environment is limited and full of errors. Therefore, nativists assume that it is impossible for children to learn linguistic information solely from their environment.[4] However, because children possess this LAD, they are in fact, able to learn language despite incomplete information from their environment. Their capacity to learn language is also attributed to the theory of universal grammar (UG), which posits that a certain set of structural rules are innate to humans, independent of sensory experience.[5] This view has dominated linguistic theory for over fifty years and remains highly influential, as witnessed by the number of articles in journals and books.[citation needed]

text: The empiricist theory suggests, contra Chomsky, that there is enough information in the linguistic input children receive and therefore, there is no need to assume an innate language acquisition device exists (see above). Rather than a LAD evolved specifically for language, empiricists believe that general brain processes are sufficient enough for language acquisition. During this process, it is necessary for the child to actively engage with their environment. For a child to learn language, the parent or caregiver adopts a particular way of appropriately communicating with the child; this is known as child-directed speech (CDS).[citation needed] CDS is used so that children are given the necessary linguistic information needed for their language. Empiricism is a general approach and sometimes goes along with the interactionist approach. Statistical language acquisition, which falls under empiricist theory, suggests that infants acquire language by means of pattern perception.[citation needed]

text: Other researchers embrace an interactionist perspective, consisting of social-interactionist theories of language development. In such approaches, children learn language in the interactive and communicative context, learning language forms for meaningful moves of communication. These theories focus mainly on the caregiver's attitudes and attentiveness to their children in order to promote productive language habits.[6]

text: An older empiricist theory, the behaviorist theory proposed by B. F. Skinner suggested that language is learned through operant conditioning, namely, by imitation of stimuli and by reinforcement of correct responses. This perspective has not been widely accepted at any time, but by some accounts, is experiencing a resurgence. New studies use this theory now to treat individuals diagnosed with autism spectrum disorders. Additionally, Relational Frame Theory is growing from the behaviorist theory, which is important for Acceptance and Commitment Therapy.[7] Some empiricist theory accounts today use behaviorist models.[8]

text: Other relevant theories about language development include Piaget's theory of cognitive development, which considers the development of language as a continuation of general cognitive development[9] and Vygotsky's social theories that attribute the development of language to an individual's social interactions and growth.[10]

text: Biological preconditions[edit]

text: Evolutionary biologists are skeptical of the claim that syntactic knowledge is transmitted in the human genome. However, many researchers claim that the ability to acquire such a complicated system is unique to the human species. Non-biologists also tend to believe that our ability to learn spoken language may have been developed through the evolutionary process and that the foundation for language may be passed down genetically. The ability to speak and understand human language requires speech production skills and abilities as well as multisensory integration of sensory processing abilities.[citation needed]

text: One hotly debated issue is whether the biological contribution includes capacities specific to language acquisition, often referred to as universal grammar. For fifty years, linguist Noam Chomsky has argued for the hypothesis that children have innate, language-specific abilities that facilitate and constrain language learning.[citation needed] In particular, he has proposed that humans are biologically prewired to learn language at a certain time and in a certain way, arguing that children are born with a language acquisition device (LAD).[11] However, since he developed the minimalist program, his latest version of theory of syntactic structure, Chomsky has reduced the elements of universal grammar, which he believes are prewired in humans to just the principle of recursion, thus voiding most of the nativist endeavor.[12]

text: Researchers who believe that grammar is learned rather than innate, have hypothesized that language learning results from general cognitive abilities and the interaction between learners and their human interactants. It has also recently been suggested that the relatively slow development of the prefrontal cortex in humans may be one reason that humans are able to learn language, whereas other species are not.[13][14] Further research has indicated the influence of the FOXP2 gene.[15]

text: Gender differences[edit]

text: Children versus adults[edit]

text: Language development and processing begins before birth. Evidence has shown that there is language development occurring antepartum. DeCasper and Spence[16] performed a study in 1986 by having mothers read aloud during the last few weeks of pregnancy. When the infants were born, they were then tested. They were read aloud a story while sucking on a pacifier; the story was either the story read by the mother when the infant was in utero or a new story. The pacifier used was able to determine the rate of sucking that the infant was performing. When the story that the mother had read before was heard, the sucking of the pacifier was modified. This did not occur during the story that the infant had not heard before. The results for this experiment had shown that the infants were able to recognize what they had heard in utero, providing insight that language development had been occurring in the last six weeks of pregnancy.

text: Throughout the first year of life, infants are unable to communicate with language. Instead, infants communicate with gestures. This phenomenon is known as prelinguistic gestures, which are nonverbal ways that infants communicate that also had a plan backed with the gesture. Examples of these could be pointing at an object, tugging on the shirt of a parent to get the parent's attention, etc. Harding,[17] 1983, devised the major criteria that come along with the behavior of prelinguistic gestures and their intent to communicate. There are three major criteria that go along with a prelinguistic gesture: waiting, persistence, and ultimately, development of alternative plans. This process usually occurs around 8 months of age, where an appropriate scenario may be of a child tugging on the shirt of a parent to wait for the attention of the parent who would then notice the infant, which causes the infant to point to something they desire. This would describe the first two criteria. The development of alternative plans may arise if the parent does not acknowledge what the infant wants, the infant may entertain itself to satisfy the previous desire.

text: When children reach about 15–18 months of age, language acquisition flourishes. There is a surge in word production resulting from the growth of the cortex. Infants begin to learn the words that form a sentence and within the sentence, the word endings can be interpreted. Elissa Newport and colleagues (1999)[18] found that humans learn first about the sounds of a language, and then move on to how to speak the language. This shows how infants learn the end of a word and know that a new word is being spoken. From this step, infants are then able to determine the structure of a language and word.

text: It appears that during the early years of language development females exhibit an advantage over males of the same age. When infants between the age of 16 to 22 months were observed interacting with their mothers, a female advantage was obvious. The females in this age range showed more spontaneous speech production than the males and this finding was not due to mothers speaking more with daughters than sons.[19] In addition, boys between 2 and 6 years as a group did not show higher performance in language development over their girl counterparts on experimental assessments. In studies using adult populations, 18 and over, it seems that the female advantage may be task dependent. Depending on the task provided, a female advantage may or may not be present.[20]

text: Lateralization effect on language[edit]

text: It is currently believed that in regards to brain lateralization males are left-lateralized, while females are bilateralized. Studies on patients with unilateral lesions have provided evidence that females are in fact more bilateralized with their verbal abilities. It seems that when a female has experienced a lesion to the left hemisphere, she is better able to compensate for this damage than a male can. If a male has a lesion in the left hemisphere, his verbal abilities are greatly impaired in comparison to a control male of the same age without that damage.[21] However, these results may also be task-dependent as well as time-dependent.[22]

text: Writing development[edit]

text: Research in writing development has been limited in psychology.[23] In the research that has been conducted, focus has generally centred on the development of written and spoken language and their connection. Spoken and written skills could be considered linked. Researchers believe that children's spoken language influences their written language.[24] When a child learns to write they need to master letter formation, spelling, punctuation and they also have to gain an understanding of the structure and the organisational patterns involved in written language.[25]

text: Kroll's theory is one of the most significant on children's writing development. He proposed that children's writing development is split into 4 phases. Kroll explicitly states that these phases are 'artificial' in the sense that the boundaries between the phases are imprecise and he recognises that each child is different, thus their development is unique.[24] The phases of writing development have been highlighted to give the reader a broad outline of what phases a child goes through during writing development; however when studying an individual's development in depth, the phases may be disregarded to an extent.

text: The first of Kroll's phases is the preparation for writing phase. In this phase the child is believed to grasp the technical skills needed for writing, allowing them to create the letters needed to write the words the children say. In this initial phase children experience many opportunities to extend their spoken language skills. Speaking and writing are considered fairly separate processes here, as children's writing is less well developed at this stage, whereas their spoken language is becoming more skilled.[24]

text: Kroll considers the second phase in writing development to be consolidation. Here, children begin to consolidate spoken and written language. In this phase children's writing skills rely heavily on their spoken language skills, and their written and spoken language becoming integrated.[24] Children's written language skills become stronger as they use their spoken language skills to improve their writing. Then in turn, when a development in children's written language skills is seen, their spoken language skills have also improved. A child's written language in this phase mirrors their spoken language.[24]

text: In the third phase, differentiation, children begin to learn that written language regularly differs in structure and style from spoken language. The growth from consolidation to differentiation can be challenging for some children to grasp.[24] Children can 'struggle with the transformation from the basically overt language of speech to the essentially covert activity of writing'.[26] In this phase, the child learns that writing is generally considered more formal than spoken language, which is thought to be casual and conversational. Here, it is believed that children begin to understand that writing serves a purpose.[27]

text: Kroll considers the last phase to be the systematic integration phase. A differentiation and integration between the child's speaking and writing can be seen in this phase. This means that speaking and writing have 'well-articulated forms and functions';[27] however, they are also integrated in the sense that they use the same system. As a result of the individual being aware of the audience, context and reason they are communicating, both written and spoken language are able to overlap and take several forms at this stage.[27]

text: Kroll used the four phases to give an explanation and generalise about the development of these two aspects of language. The highest significance is placed on the second and third phase, consolidation and differentiation respectively.[27] It could be concluded that children's written and spoken language, in certain respects, become more similar to age, maturation, and experience; however, they are also increasingly different in other respects. The content of the skills are more similar, but the approach used for both writing and speaking are different.[27] When writing and speaking development is looked at more closely it can be seen that certain elements of written and spoken language are differentiating and other elements are integrating, all in the same phase.

text: Perera conducted a survey and her view mirrors that of Kroll to the extent that she used Kroll's four phases.[25] When a child undergoes initial learning of the written language, they have not yet fully mastered the oral language.[25] It is clear that their written language development is aided by their spoken language; it can also be said that their spoken language development is aided by the development of their written language skills. Kantor and Rubin believe that not all individuals successfully move into the final stage of integration.[28] Perera is also aware that it is hard to assign chronological ages to each phase of writing development, because each child is an individual, and also the phases are 'artificial'.

text: More recent research has also explored writing development. Myhill concentrated on the development of written language skills in adolescents aged 13 to 15.[29] Myhill discovered that the more mature writer was aware of the shaping of text, and used non-finite clauses, which mirrored Perera's results (1984).[29] Other researchers focused on writing development up until late adolescence, as there has been a limited research in this area.[23] Chrisite and Derewianke recognize that the survey conducted by Perera (1984) is still one of the most significant research studies in the writing development field and believe Perera's study is similar to theirs. Chrisite and Derewianke (2010) again propose four phases of writing development. The researchers believe that the process of writing development does not stop when an individual leaves formal education, and again, the researchers highlight that these phases are flexible in their onset. The first phase focuses on spoken language as the main aid for writing development, and the development then takes its course reaching the fourth phase, which continues beyond formal education.[23]

text: Environmental influences[edit]

text: The environment a child develops in has influences on language development. The environment provides language input for the child to process. Speech by adults to children help provide the child with correct language usage repetitively.[citation needed] Environmental influences on language development are explored in the tradition of social interactionist theory by such researchers as Jerome Bruner, Alison Gopnik, Andrew Meltzoff, Anat Ninio, Roy Pea, Catherine Snow, Ernest Moerk and Michael Tomasello. Jerome Bruner who laid the foundations of this approach in the 1970s, emphasized that adult "scaffolding" of the child's attempts to master linguistic communication is an important factor in the developmental process.[citation needed]

text: One component of the young child's linguistic environment is child-directed speech (also known as baby talk or motherese), which is language spoken in a higher pitch than normal with simple words and sentences. Although the importance of its role in developing language has been debated, many linguists think that it may aid in capturing the infant's attention and maintaining communication.[30] When children begin to communicate with adults, this motherese speech allows the child the ability to discern the patterns in language and to experiment with language.

text: Throughout research done, it is concluded that children exposed to extensive vocabulary and complex grammatical structures more quickly develop language and also have a more accurate syntax than children raised in environments without complex grammar exposed to them. With motherese, the mother talks to the child and responds back to the child, whether it be a babble the child made or a short sentence. While doing this, the adult prompts the child to continue communicating, which may help a child develop language sooner than children raised in environments where communication is not fostered.[citation needed]

text: Child-directed speech concentrates on small core vocabulary, here and now topics, exaggerated facial expressions and gestures, frequent questioning, paralinguistic changes, and verbal rituals.[31] An infant is least likely to produce vocalizations when changed, fed, or rocked. The infant is more likely to produce vocalizations in response to a nonverbal behavior such as touching or smiling.[citation needed]

text: Child-directed speech also catches the child's attention, and in situations where words for new objects are being expressed to the child, this form of speech may help the child recognize the speech cues and the new information provided. Data shows that children raised in highly verbal families had higher language scores than those children raised in low verbal families. Continuously hearing complicated sentences throughout language development increases the child's ability to understand these sentences and then to use complicated sentences as they develop. Studies have shown that students enrolled in high language classrooms have two times the growth in complex sentences usage than students in classrooms where teachers do not frequently use complex sentences.[citation needed]

text: Adults use strategies other than child-directed speech like recasting, expanding, and labeling:

text:
Recasting is rephrasing something the child has said, perhaps turning it into a question or restating the child's immature utterance in the form of a fully grammatical sentence. For example, a child saying "cookie now" a parent may respond with "Would you like a cookie now?"[32]
Expanding is restating, in a linguistically sophisticated form, what a child has said. For example, a child may say "car move road" and the parent may respond "A car drives on the road."[citation needed]
Labeling is identifying the names of objects.[11] If a child points to an object such as a couch the mother may say "couch" in response. Labeling can also be characterized as referencing.[31]

text: Some language development experts have characterized child directed speech in stages. Primarily, the parents use repetition and also variation to maintain the infant's attention. Secondly, the parent simplifies speech to help in language learning. Third, any speech modifications maintain the responsiveness of the child. These modifications develop into a conversation that provides context for the development.[31]

text: Cultural and socioeconomic effects[edit]

text: While most children throughout the world develop language at similar rates and without difficulty, cultural and socioeconomic differences have been shown to influence development. An example of cultural differences in language development can be seen when comparing the interactions of mothers in the United States with their infants with mothers in Japan.[33] Mothers in the United States use more questions, are more information-oriented, and use more grammatically correct utterances with their 3-month-olds.[citation needed] Mothers in Japan, on the other hand, use more physical contact with their infants, and more emotion-oriented, nonsense, and environmental sounds, as well as baby talk, with their infants. These differences in interaction techniques reflect differences in "each society's assumptions about infants and adult-to-adult cultural styles of talking."[31]

text: Specifically in North American culture, maternal race, education, and socioeconomic class influence parent-child interactions in the early linguistic environment.[citation needed] When speaking to their infants, mothers from middle class "incorporate language goals more frequently in their play with their infants," and in turn, their infants produce twice as many vocalizations as lower class infants.[31] Mothers from higher social classes who are better educated also tend to be more verbal, and have more time to spend engaging with their infants in language. Additionally, lower class infants may receive more language input from their siblings and peers than from their mothers.[citation needed]

text: Social preconditions[edit]

text: It is crucial that children are allowed to socially interact with other people who can vocalize and respond to questions. For language acquisition to develop successfully, children must be in an environment that allows them to communicate socially in that language. Children who have learnt sound, meaning and grammatical system of language that can produce clear sentence may still not have the ability to use language effectively in various social circumstance. Social interaction is the footing stone of language.[34]

text: There are a few different theories as to why and how children develop language. The most popular—and yet heavily debated—explanation is that language is acquired through imitation. This theory has been challenged by Lester Butler, who argues that children do not use the grammar that an adult would use. Furthermore, "children's language is highly resistant to alteration by adult intervention", meaning that children do not use the corrections given to them by an adult.[35] The two most accepted theories in language development are psychological and functional.[citation needed] Psychological explanations focus on the mental processes involved in childhood language learning. Functional explanations look at the social processes involved in learning the first language.

text: Different aspects[edit]

text:
Phonology involves the rules about the structure and sequence of speech sounds.
Semantics consists of vocabulary and how concepts are expressed through words.
Grammar involves two parts.

text:
The first, syntax, is the rules in which words are arranged into sentences.
The second, morphology, is the use of grammatical markers (indicating tense, active or passive voice etc.).

text:
Pragmatics involves the rules for appropriate and effective communication. Pragmatics involves three skills:

using language for greeting, demanding etc.,
changing language for talking differently depending on who it is you are talking to;
following rules such as turn taking, staying on topic.

text: Each component has its own appropriate developmental periods.

text: Phonological development[edit]

text: Babies can recognize their mother's voice from as early as few weeks old. It seems like they have a unique system that is designed to recognize speech sound. Furthermore, they can differentiate between certain speech sounds. A significant first milestone in phonetic development is the babbling stage (around the age of six months). This is the baby's way of practicing his control over that apparatus. Babbling is independent from the language. Deaf children for instance, babble the same way as hearing ones. As the baby grows older, the babbling increases in frequency and starts to sound more like words (around the age of twelve months). Although every child is an individual with different pace of mastering speech, there is a tendency to an order of which speech sounds are mastered:

text:
Vowels before consonants
Stop sounds before any other consonant sounds (for example: 'p','t','b')
Place of articulation – labials, alveolar, velars, alovepalatals, and interdentals in that order by the age of 4. That means that there is some order to the development of the physical system in young children.

text: Early phonetic processes[edit]

text: As the children's ability to produce sound develops, their ability to perceive the phonetic contrast of their language develops. The better they get in mastering the sound, the more sensitive they become to the changes in those sounds in their language once they get exposed to it. They learn to isolate individual phenomes while speaking which also serves as the basis of reading.

text: Some processes that occur in early age:

text:
Syllable deletion – stressed syllables are emphasis that may be given to certain syllables in a word. They are more likely to be retained in children's pronunciation than unstressed syllables (less emphasis on the sound) because they are more salient to children in an early language acquisition process. So children may say helikat instead of helicopter or fowe instead of telephone. That way, they don't pronounce the more emphasized sound in the word.
Syllable simplification – another process that happens in order to simplify syllable structure, children delete certain sounds systematically. For example, children might say 'tap' instead of "stop" and completely drop the 's' sound in that word. That is a common process in children's speech development.
Substitution – systematic replacement of one sound by an alternative, easier one to articulate (substitution process – stopping, fronting, gliding). It means that the young toddler may use sounds that are easier to produce instead of the proper sound in a word. We may see that the child replace the 'r' sound with 'l' or 'w', the 'n' with 'd' and so on.
Assimilation – modification of segments of the word influenced by neighboring sounds, due to ease of articulation. In order for the young speaker to produce sounds easier, he or she may replace the sound in a specific word to a different one, which is somewhat similar. For example, the word "pig" may sound as "big" – 'p' and 'b' are close in their sound. (Lightbown, Spada, Ranta & Rand, 2006).

text: From shortly after birth to around one year, the baby starts to make speech sounds. At around two months, the baby engages in cooing, which mostly consists of vowel sounds. At around four months, cooing turns into babbling, which is the repetitive consonant-vowel combinations. Babies understand more than they are able to say. In this 0–8 months range, the child is engaged in vocal play of vegetative sounds, laughing, and cooing.[citation needed]

text: Once the child hits the 8–12 month, range the child engages in canonical babbling, i.e. dada as well as variegated babbling. This jargon babbling with intonational contours the language being learned.[citation needed]

text: From 12–24 months, babies can recognize the correct pronunciation of familiar words. Babies also use phonological strategies to simplify word pronunciation. Some strategies include repeating the first consonant-vowel in a multisyllable word ('TV' → 'didi') or deleting unstressed syllables in a multisyllable word ('banana'-->'nana'). Within this first year, two word utterances and two syllable words emerge. This period is often called the holophrastic stage of development, because one word conveys as much meaning as an entire phrase. For instance, the simple word "milk" can imply that the child is requesting milk, noting spilled milk, sees a cat drinking milk, etc.[36]

text: By 24–30 months awareness of rhyme emerges as well as rising intonation.[citation needed]

text: By 36–60 months, phonological awareness continues to improve as well as pronunciation.[citation needed] At this age, children have a considerable experience with language and are able to form simple sentences that are 3 words in length. They use basic prepositions, pronouns, and plurals. They become immensely creative in their language use and learn to categorize items such as recognizing that a shoe is not a fruit. At this age, children also learn to ask questions and negate sentences to develop these questions. Over time, their syntax gets more and more unique and complex.

text: By 6–10 years, children can master syllable stress patterns, which helps distinguish slight differences between similar words.[citation needed]

text: Semantic development[edit]

text: The average child masters about fifty words by the age of eighteen months. These might include words such as, milk, water, juice and apple (noun-like words). Afterwards they acquire 12 to 16 words a day. By the age of six, they master about 13 to 14 thousand words.

text: The most frequent words include adjective-like expressions for displeasure and rejection such as 'no'. They also include social interaction words, such as "please" and "bye".

text: There are three stages for learning the meaning of new words:

text:
Whole object assumption:
A new word refers to a whole object. For example, when an eighteen-months old child sees a sheep and his mother points at it and says the word 'sheep', the child infers that the word 'sheep' describes the whole animal and not parts of it (such as color, shape, etc.).
Type assumption:
A new word refers to a type of thing, not just to a particular thing. For example, when the child hears the word 'sheep' he infers that it is used for the animal type and not only for that particular sheep that he saw.
Basic level assumption:
A new word refers to objects that are alike in basic ways (appearance, behavior, etc.).

text: In other words, when the child hears the word "sheep" he overgeneralizes it to other animals that look like sheep by the external appearance, such as white, wooly and four-legged animal.

text: Contextual clues are a major factor in the child's vocabulary development.

text: The child uses contextual clues to draw inferences about the category and meaning of new words. By doing so, the child distinguishes between names and ordinary nouns.

text: For example, when an object is presented to the child with the determiner "a" (a cat, a dog, a bottle) he perceives it as an ordinary noun.

text: However, when the child hears a noun without the determiner, he perceives it as a name, for instance "this is Mary".

text: Children usually make correct meaning associations with the words that the adults say. However, sometimes they make semantic errors.

text: There are a few types of semantic errors:

text: Overextension: When a child says or hears a word, they might associate what they see or hear as more generalized concept than the real meaning of the word. For example, if they say "cat", they might overextend it to other animals with same features.

text: Underextension: It involves the use of lexical items in an overly restrictive fashion. In other words, the child focuses on core members of a certain category. For example: 'cat' may only refer to the family cat and no other cat, or 'dog' may refer to certain kinds of dogs that the child is exposed to.

text: Verb meaning: when a pre-school child hears the verb 'fill', he understands it as the action 'pour' rather than the result, which is 'make full'.

text: Dimensional terms: the first dimensional adjectives acquired are big and small because they belong to the size category. The size category is the most general one. Later children acquire the single dimension adjectives, such as, tall-short, long-short, high-low. Eventually they acquire the adjectives that describe the secondary dimension, such as thick-thin, wide-narrow and deep-shallow.

text: From birth to one year, comprehension (the language we understand) develops before production (the language we use). There is about a 5-month lag in between the two. Babies have an innate preference to listen to their mother's voice. Babies can recognize familiar words and use preverbal gestures.[citation needed]

text: Within the first 12–18 months semantic roles are expressed in one word speech including agent, object, location, possession, nonexistence and denial. Words are understood outside of routine games but the child still needs contextual support for lexical comprehension.[37]

text: 18–24 months Prevalent relations are expressed such as agent-action, agent-object, action-location.[37] Also, there is a vocabulary spurt between 18–24 months, which includes fast mapping. Fast mapping is the babies' ability to learn a lot of new things quickly. The majority of the babies' new vocabulary consists of object words (nouns) and action words (verbs).

text: 30–36 months The child is able to use and understand why question and basic spatial terms such as in, on or under.[citation needed]

text: 36–42 months There is an understanding of basic color words and kinship terms. Also, the child has an understanding of the semantic relationship between adjacent and conjoined sentences, including casual and contrastive.[citation needed]

text: 42–48 months When and how questions are comprehended as well as basic shape words such as circle, square and triangle.[citation needed]

text: 48–60 months Knowledge of letter names and sounds emerges, as well as numbers.

text: By 3–5 years, children usually have difficulty using words correctly. Children experience many problems such as underextensions, taking a general word and applying it specifically (for example, 'cartoons' specifically for 'Mickey Mouse') and overextensions, taking a specific word and applying it too generally (example, 'ant' for any insect). However, children coin words to fill in for words not yet learned (for example, someone is a cooker rather than a chef because a child may not know what a chef is). Children can also understand metaphors.[citation needed]

text: From 6–10 years, children can understand meanings of words based on their definitions. They also are able to appreciate the multiple meanings of words and use words precisely through metaphors and puns. Fast mapping continues.[citation needed] Within these years, children are now able to acquire new information from written texts and can explain relationships between multiple meaning words. Common idioms are also understood.

text: Syntactic development[edit]

text: The development of syntactic structures follows a particular pattern and reveals much on the nature of language acquisition, which has several stages. According to O'Grady and Cho (2011), the first stage, occurring between the ages of 12–18 months, is called "one-word stage." In this stage, children cannot form syntactic sentences and therefore use one-word utterances called "holophrases" that express an entire sentence. In addition, children's comprehension is more advanced than their production abilities. For example, a child who wants candy may say "candy" instead of expressing a full sentence.

text: The following stage is the "two-word stage" in which children begin to produce "mini-sentences" that are composed of two words, such as "doggy bark" and "Ken water" (O'Grady & Cho, 2011, p. 346). At this stage, it is unclear whether children have an understanding of underlying rules of the language such as syntactic categories, since their "mini-sentences" often lack distinction between the categories. However, children do exhibit sensitivity to sentence structures and they frequently use appropriate word order.

text: After several months of speech that is restricted to short utterances, children enter the "telegraphic stage" and begin to produce longer and more complex grammatical structures (O'Grady & Cho, 2011, p. 347). This stage is characterized by production of complex structures as children begin to form phrases consisting of a subject and a complement in addition to use of modifiers and composition of full sentences. Children use mostly content words and their sentences lack function words. For example, a child may say "fill cup water," instead of saying, "Fill my cup with water." Subsequently, language acquisition continues to develop rapidly and children begin to acquire complex grammar that shows understanding of intricate linguistic features, such as the ability to switch the position of words in sentences.

text: Throughout the process of syntactic development, children acquire and develop question structures. According to O'Grady and Cho (2011), at the early stages of language acquisition, children ask yes-no questions by rising intonation alone as they develop awareness to auxiliary verbs only at a later stage. When auxiliary verbs make their appearance, it takes children a few months before they are able to use inversion in yes-no questions. The development of WH- questions occurs between the ages of two and four, when children acquire auxiliary verbs that then leads to the ability to use inversion in questions. However, some children find inversion easier in yes-no questions than in WH- questions, since the position of the WH- word and the auxiliary verb both must changed (e.g., "You are going where?" instead of "Where are you going?").

text: Morphological development[edit]

text: Morphological structures development occurs over a period of several years. Before language is acquired, children lack any use of morphological structures.

text: The morphological structures that children acquire during their childhood, and even up to the early school years, are: determiners (a, the), -ing inflection, plural –s, auxiliary be, possessive –s, third person singular –s, past tense –ed).

text: When children start using them they tend to overgeneralize the rules and project them upon all the words in the language, including irregulars. For example: if a child knows the –ed (past tense) there is a possibility that they'll say "I eated"( Man-mans cat-cats). These errors result from overgeneralization of rules.

text: This overgeneralization is very noticeable, in fact, children do that in less than 25 percent of the time at any point before reducing that percentage. Then they improve their mastery, which can be tested in various ways, such as the "wug test" (Berko, 1958).

text: Children often figure out quickly frequent irregular verbs, such as go and buy rather than less common ones, such as win. This suggests that children must hear the word several hundred times before they are able to use it correctly.

text: This development of bound morphemes is similar in order among children, for example: -ing is acquired before the article the. The interesting part though is that parents tend to use a different order while speaking to their kids, for example, parents use the article 'the' more frequently than -ing. Meaning, other factors determine the order of acquisition, such as:

text:
Morphemes that come at the end of an utterance are remembered better.
Children seem to remember morphemes such as –ing better because they contain their own syllables rather than single consonant morpheme, such as plural –s.
Affixes with more than one meaning are more difficult to acquire, e.g., –s functions both as plural noun and singular third.

text: As it comes to word formation processes such as derivation and compounding, the earliest derivational suffixes to show up in children's speech are those they hear adults use most frequently. (-er as the *'doer' of the action such as walker.) When it comes to compounds, children first make up names for agents and instruments that they don't know by a pattern (N-N), though some of them do not follow the pattern (*cutter grass for grass cutter). Then, they might have the right structure but the words are inappropriate since English already has words with the intended meaning such as car-smoke = exhaust. This process points to a preference for building words from other words, thus place less demand on memory than learning an entirely new word for each concept.[citation needed]

text: Grammatical development[edit]

text: Grammar describes the way sentences of a language are constructed, which includes both syntax and morphology.[38]

text: Syntactic development and morphological development[edit]

text: Syntactic development involves the ways that various morphemes are ordered or combined in sentences.[39]Morphemes, which are basic units of meaning in language, get added as children learn to produce simple sentences and become more precise speakers. Morphemes can be whole words (like "happy") or parts of words that change meaning of words ("un"happy). Brown[40] proposed a stage model that describes the various types of morphological structures that are developed in English and the age range within which they are normally acquired.[41]

text: Stage I: From 15–30 months, children start using telegraphic speech, which are two word combinations, for example 'wet diaper'. Brown (1973)[40] observed that 75% of children's two-word utterances could be summarized in the existence of 11 semantic relations:[40][41]

text:
Attributive: 'Big house'
Agent-action: 'Daddy hit'
Action-object: 'Hit ball'
Agent-object: 'Daddy ball'
Nominative: 'That ball'
Demonstrative: 'There ball'
Recurrence: 'More ball'
Non-existence: 'All-gone ball'
Possessive: 'Daddy chair'
Entity + Locative: 'book table'
Action + Locative: 'go store'

text: Stage II: At around 28–36 months, children begin to engage in the production of simple sentences, usually 3 word sentences. These simple sentences follow syntactic rules and are refined gradually as development[41] continues. The morphological developments seen in this age range include use of present progressive (-ing endings), the prepositions "in" and "on", and regular plurals (-s endings).[41]

text: Stage III: Around 36–42 months, children continue to add morphemes and gradually produce complex grammatical structures.[41] The morphemes that are added at this age include irregular past tense, possessive ('s), and use of the verb 'to be' (It is, I am, etc.).[41]

text: Stage IV:Around 40–46 months children continue to add to their morphological knowledge. This range is associated with use of articles (a or the), regular past tense (-ed endings), and regular third person speech (He likes it).[41]

text: Stage V: Around 42-52+ months children refine the complex grammatical structures and increase their use of morphemes to convey more complex ideas. Children in this stage use irregular third-person speech, the verb 'to be' as an auxiliary verb (She was not laughing), and in its contraction forms (It's, She's, etc.).[41]

text: Pragmatics development[edit]

text: From birth to one year, babies can engage in joint attention (sharing the attention of something with someone else). Babies also can engage in turn taking activities.[citation needed]

text:
By 1–2 years, they can engage in conversational turn taking and topic maintenance.[citation needed]
By age 3–5, children can master illocutionary intent, knowing what you meant to say even though you might not have said it and turnabout, which is turning the conversation over to another person.[citation needed]
By age 6–10, shading occurs, which is changing the conversation topic gradually. Children are able to communicate effectively in demanding settings, such as on the telephone.[citation needed]

text: Effect of bilingualism[edit]

text: There is a large debate regarding whether or not bilingualism is truly beneficial to children. Parents of children often view learning a second language throughout elementary and high school education beneficial to the child.[42] Another perspective dictates that the second language just confuses the child and prevents them from mastering their primary language.[43] Studies have shown that American bilingual children have greater cognitive flexibility, better perceptual skills and tend to be divergent thinkers than monolingual children between the ages of five to ten.[42][43] Better executive functioning skills are likely because bilingual children have to choose one language to speak while actively suppressing the other. This builds stronger selective attention and cognitive flexibility because these skills are being exercised more.[44] In addition, bilingual children have a better understanding of universal language concepts, such as grammar, because these concepts are applied in multiple languages.[45] However, studies comparing Swedish-Finnish bilingual children and Swedish monolingual children between the ages of five to seven have also shown that the bilingual children have a smaller vocabulary than monolingual children.[46] In another study throughout America, elementary school English-monolingual children performed better in mathematics and reading activities than their non-English-dominant bilingual and non-English monolingual peers from kindergarten to grade five.[47] Learning two languages simultaneously can be beneficial or a hindrance to a child's language and intellectual development. Further research is necessary to continue to shed light on this debate.

text: In addition to the study of bilingualism in children, similar research is being conducted in adults. Research findings show that although bilingual benefits are muted in middle adulthood,[42] they are more profound in older age when those who develop dementia experience onset about 4.5 years later in bilingual subjects.[48] The increased attentional control, inhibition, and conflict resolution developed from bilingualism may be accountable for the later onset of dementia.[42]

text: Language disorders[edit]

text: A language disorder is the impaired comprehension and or use of a spoken, written, and/or other symbol system. A disorder may involve problems in the following areas:

text:
The form of language i.e. phonology, morphology, or syntax[citation needed]
The content i.e. semantics[citation needed]
The function of language in communication i.e. pragmatics[citation needed]

text: Olswang and colleagues have identified a series of behaviors in children in the 18–36 month range that are predictors for the need of language intervention.[49]

text: These predictors include:

text:
A smaller than average vocabulary
A language comprehension delay of 6 months or a comprehension deficit with a large comprehension production gap
Phonological problems such as restricted babbling or limited vocalizations
Few spontaneous vocal imitations and reliance on direct modeling in imitation tasks
Little combinatorial or symbolic play
Few communicative or symbolic gestures
Behavior problems[49]

text: Some of the many conditions that cause language development problems include:

text:
Attention deficit hyperactivity disorder
Auditory processing disorder
Autism
Developmental verbal dyspraxia
Language delay
Otitis media
Pragmatic language impairment
Specific language impairment
Speech delay
Speech disorder
Speech sound disorder
Speech repetition


document_title: Qutb Minar

question_text: who built the fifth floor of qutub minar

root

text: Qutb Minar

text: History[edit]

text: Qutab Minar was established along with Quwwat-ul-Islam Mosque around 1192 by Qutab-ud-din Aibak, first ruler of the Delhi Sultanate.[6] The mosque complex is one of the earliest that survives in the Indian subcontinent.[7][8] The minaret is named after Qutab-ud-din Aibak, or Qutabuddin Bakhtiar Kaki, a Sufi saint.[9] Its ground storey was built over the ruins of the Lal Kot, the citadel of Dhillika.[10] Aibak's successor Iltutmish added three more storeys.[9] The minar's topmost storey was damaged by lightning in 1369 and was rebuilt by Firoz Shah Tughlaq, who added another storey. In 1505, an earthquake damaged Qutub Minar; it was repaired by Sikander Lodi. On 1 September 1803, a major earthquake caused serious damage. Major Robert Smith of the British Indian Army renovated the tower in 1828 and installed a pillared cupola over the fifth story, thus creating a sixth. The cupola was taken down in 1848, under instructions from The Viscount Hardinge, then Governor General of India. It was reinstalled at ground level to the east of Qutab Minar, where it remains. It is known as "Smith's Folly".[11]

tag: p

text: Architecture[edit]

text: The tower's style is basically Iranian, though likely patterned on Afghanistan's Minaret of Jam, and adapted to local artistic conventions by the incorporation of "looped bells and garlands and lotus borders into the carving".[12] Aybak also started Qutub Minar along the patterns of Iranian minarets but built by Hindus artisans.[13] Numerous inscriptions in Parso-Arabic and Nagari characters in different sections of the Qutab Minar reveal the history of its construction, and the later restorations and repairs by Firoz Shah Tughluq (1351–89) and Sikandar Lodi[14] (1489–1517).

text: The tower has five superposed, tapering storeys. The lowest three comprise fluted cylindrical shafts or columns of pale red sandstone, separated by flanges and by storeyed balconies, carried on Muqarnas corbels. The fourth column is of marble, and is relatively plain. The fifth is of marble and sandstone. The flanges are a darker red sandstone throughout, and are engraved with Quranic texts and decorative elements. The whole tower contains a spiral staircase of 379 steps.[15] At the foot of the tower is the Quwwat ul Islam Mosque. The minar tilts just over 65 cm from the vertical, which is considered to be within safe limits, although experts have stated that monitoring is needed in case rainwater seepage further weakens the foundation.[16]

text: Accident[edit]

text: Before 1974, the general public was allowed access to the top of the minaret, via the internal staircase. On 4 December 1981, the staircse lighting failed. Between 300 and 400 visitors stampeded towards the exit, and 45 were killed in the crush and some were injured. Most of these were children.[17] Since then, the tower has been closed to the public.[18]

text: In Literature[edit]

text:
Wikisource has original text related to this article:
'The Cootub Minah, Delhi',
a poem by L. E. L.

tag: table

text: Letitia Elizabeth Landon's poem The Cootub Minah, Delhi is a reflection on an engraving in Fisher's Drawing Room Scrap Book, 1833.

text: In popular culture[edit]

text: Bollywood actor and director Dev Anand wanted to shoot the song "Dil Ka Bhanwar Kare Pukar" from his film Tere Ghar Ke Samne inside the Minar. However, the cameras in that era were too big to fit inside the tower's narrow passage, and therefore the song was shot inside a replica of the tower.[19] The site served as the pit stop of the second leg of the second series of The Amazing race Australia.

text: A picture of the minaret is featured on the travel cards issued by the Delhi Metro Rail Corporation. A recently launched start-up in collaboration with the Archaeological survey of India has made a 360o walkthrough of Qutab Minar available.[20]

text: Gallery[edit]

text:
The Minar in context: Alai Darwaza (left), Imam Zamin's tomb (right), Qutb Minar (back)

Entrance to Minar

Calligraphy on upper-base section

Decorative motifs on upper levels

Close-up of balcony

Smith's cupola (foreground, right), with the Tomb of Imam Zamin, Alai Darwaza, and Qutb Minar in background

tag: ul


document_title: Asteroid

question_text: the asteroids that cross the orbit of earth belong to a group called the

question_tokens: the asteroids that cross the orbit of earth belong to a group called the

text: Asteroid

text: Discovery[edit]

text: The first asteroid to be discovered, Ceres, was originally considered to be a new planet.[note 1] This was followed by the discovery of other similar bodies, which, with the equipment of the time, appeared to be points of light, like stars, showing little or no planetary disc, though readily distinguishable from stars due to their apparent motions. This prompted the astronomer Sir William Herschel to propose the term "asteroid",[note 2] coined in Greek as ἀστεροειδής, or asteroeidēs, meaning 'star-like, star-shaped', and derived from the Ancient Greek ἀστήρ astēr 'star, planet'. In the early second half of the nineteenth century, the terms "asteroid" and "planet" (not always qualified as "minor") were still used interchangeably. [note 3]

text: Historical methods[edit]

text: This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (January 2018) (Learn how and when to remove this template message)

text: Asteroid discovery methods have dramatically improved over the past two centuries.

text: In the last years of the 18th century, Baron Franz Xaver von Zach organized a group of 24 astronomers to search the sky for the missing planet predicted at about 2.8 AU from the Sun by the Titius-Bode law, partly because of the discovery, by Sir William Herschel in 1781, of the planet Uranus at the distance predicted by the law. This task required that hand-drawn sky charts be prepared for all stars in the zodiacal band down to an agreed-upon limit of faintness. On subsequent nights, the sky would be charted again and any moving object would, hopefully, be spotted. The expected motion of the missing planet was about 30 seconds of arc per hour, readily discernible by observers.

text: The first object, Ceres, was not discovered by a member of the group, but rather by accident in 1801 by Giuseppe Piazzi, director of the observatory of Palermo in Sicily. He discovered a new star-like object in Taurus and followed the displacement of this object during several nights. Later that year, Carl Friedrich Gauss used these observations to calculate the orbit of this unknown object, which was found to be between the planets Mars and Jupiter. Piazzi named it after Ceres, the Roman goddess of agriculture.

text: Three other asteroids (2 Pallas, 3 Juno, and 4 Vesta) were discovered over the next few years, with Vesta found in 1807. After eight more years of fruitless searches, most astronomers assumed that there were no more and abandoned any further searches.[citation needed]

text: However, Karl Ludwig Hencke persisted, and began searching for more asteroids in 1830. Fifteen years later, he found 5 Astraea, the first new asteroid in 38 years. He also found 6 Hebe less than two years later. After this, other astronomers joined in the search and at least one new asteroid was discovered every year after that (except the wartime years 1944 and 1945). Notable asteroid hunters of this early era were J. R. Hind, Annibale de Gasparis, Robert Luther, H. M. S. Goldschmidt, Jean Chacornac, James Ferguson, Norman Robert Pogson, E. W. Tempel, J. C. Watson, C. H. F. Peters, A. Borrelly, J. Palisa, the Henry brothers and Auguste Charlois.

text: In 1891, Max Wolf pioneered the use of astrophotography to detect asteroids, which appeared as short streaks on long-exposure photographic plates. This dramatically increased the rate of detection compared with earlier visual methods: Wolf alone discovered 248 asteroids, beginning with 323 Brucia, whereas only slightly more than 300 had been discovered up to that point. It was known that there were many more, but most astronomers did not bother with them, calling them "vermin of the skies",[13] a phrase variously attributed to Eduard Suess[14] and Edmund Weiss.[15] Even a century later, only a few thousand asteroids were identified, numbered and named.

text: Manual methods of the 1900s and modern reporting[edit]

text: Until 1998, asteroids were discovered by a four-step process. First, a region of the sky was photographed by a wide-field telescope, or astrograph. Pairs of photographs were taken, typically one hour apart. Multiple pairs could be taken over a series of days. Second, the two films or plates of the same region were viewed under a stereoscope. Any body in orbit around the Sun would move slightly between the pair of films. Under the stereoscope, the image of the body would seem to float slightly above the background of stars. Third, once a moving body was identified, its location would be measured precisely using a digitizing microscope. The location would be measured relative to known star locations.[16]

text: These first three steps do not constitute asteroid discovery: the observer has only found an apparition, which gets a provisional designation, made up of the year of discovery, a letter representing the half-month of discovery, and finally a letter and a number indicating the discovery's sequential number (example: 1998 FJ74).

text: The last step of discovery is to send the locations and time of observations to the Minor Planet Center, where computer programs determine whether an apparition ties together earlier apparitions into a single orbit. If so, the object receives a catalogue number and the observer of the first apparition with a calculated orbit is declared the discoverer, and granted the honor of naming the object subject to the approval of the International Astronomical Union.

text: Computerized methods[edit]

text: There is increasing interest in identifying asteroids whose orbits cross Earth's, and that could, given enough time, collide with Earth (see Earth-crosser asteroids). The three most important groups of near-Earth asteroids are the Apollos, Amors, and Atens. Various asteroid deflection strategies have been proposed, as early as the 1960s.

text: The near-Earth asteroid 433 Eros had been discovered as long ago as 1898, and the 1930s brought a flurry of similar objects. In order of discovery, these were: 1221 Amor, 1862 Apollo, 2101 Adonis, and finally 69230 Hermes, which approached within 0.005 AU of Earth in 1937. Astronomers began to realize the possibilities of Earth impact.

text: Two events in later decades increased the alarm: the increasing acceptance of the Alvarez hypothesis that an impact event resulted in the Cretaceous–Paleogene extinction, and the 1994 observation of Comet Shoemaker-Levy 9 crashing into Jupiter. The U.S. military also declassified the information that its military satellites, built to detect nuclear explosions, had detected hundreds of upper-atmosphere impacts by objects ranging from one to ten meters across.

text: All these considerations helped spur the launch of highly efficient surveys that consist of charge-coupled device (CCD) cameras and computers directly connected to telescopes. As of 2011[update], it was estimated that 89% to 96% of near-Earth asteroids one kilometer or larger in diameter had been discovered.[17] A list of teams using such systems includes:[18]

text:
Lincoln Near-Earth Asteroid Research (LINEAR)
Near-Earth Asteroid Tracking (NEAT)
Spacewatch
Lowell Observatory Near-Earth-Object Search (LONEOS)
Catalina Sky Survey (CSS)
Campo Imperatore Near-Earth Object Survey (CINEOS)
Japanese Spaceguard Association
Asiago-DLR Asteroid Survey (ADAS)
Pan-STARRS

text: As of 20 September 2013[update], the LINEAR system alone has discovered 138,393 asteroids.[19] Among all the surveys, 4711 near-Earth asteroids have been discovered[20] including over 600 more than 1 km (0.6 mi) in diameter.

text: Terminology[edit]

text: Traditionally, small bodies orbiting the Sun were classified as comets, asteroids, or meteoroids, with anything smaller than ten meters across being called a meteoroid. Beech and Steel's 1995 paper proposed a meteoroid definition including size limits.[21][22] The term "asteroid", from the Greek word for "star-like", never had a formal definition, with the broader term minor planet being preferred by the International Astronomical Union.

text: However, following the discovery of asteroids below ten meters in size, Rubin and Grossman's 2010 paper revised the previous definition of meteoroid to objects between 10 µm and 1 meter in size in order to maintain the distinction between asteroids and meteoroids.[4] The smallest asteroids discovered (based on absolute magnitude H) are 2008 TS26 with H = 33.2 and 2011 CQ1 with H = 32.1 both with an estimated size of about 1 meter.[23]

text: In 2006, the term "small Solar System body" was also introduced to cover both most minor planets and comets.[note 4][24] Other languages prefer "planetoid" (Greek for "planet-like"), and this term is occasionally used in English especially for larger minor planets such as the dwarf planets as well as an alternative for asteroids since they are not star-like.[25] The word "planetesimal" has a similar meaning, but refers specifically to the small building blocks of the planets that existed when the Solar System was forming. The term "planetule" was coined by the geologist William Daniel Conybeare to describe minor planets,[26] but is not in common use. The three largest objects in the asteroid belt, Ceres, Pallas, and Vesta, grew to the stage of protoplanets. Ceres is a dwarf planet, the only one in the inner Solar System.

text: When found, asteroids were seen as a class of objects distinct from comets, and there was no unified term for the two until "small Solar System body" was coined in 2006. The main difference between an asteroid and a comet is that a comet shows a coma due to sublimation of near surface ices by solar radiation. A few objects have ended up being dual-listed because they were first classified as minor planets but later showed evidence of cometary activity. Conversely, some (perhaps all) comets are eventually depleted of their surface volatile ices and become asteroid-like. A further distinction is that comets typically have more eccentric orbits than most asteroids; most "asteroids" with notably eccentric orbits are probably dormant or extinct comets.[27]

text: For almost two centuries, from the discovery of Ceres in 1801 until the discovery of the first centaur, Chiron in 1977, all known asteroids spent most of their time at or within the orbit of Jupiter, though a few such as Hidalgo ventured far beyond Jupiter for part of their orbit. When astronomers started finding more small bodies that permanently resided further out than Jupiter, now called centaurs, they numbered them among the traditional asteroids, though there was debate over whether they should be considered asteroids or as a new type of object. Then, when the first trans-Neptunian object (other than Pluto), Albion, was discovered in 1992, and especially when large numbers of similar objects started turning up, new terms were invented to sidestep the issue: Kuiper-belt object, trans-Neptunian object, scattered-disc object, and so on. These inhabit the cold outer reaches of the Solar System where ices remain solid and comet-like bodies are not expected to exhibit much cometary activity; if centaurs or trans-Neptunian objects were to venture close to the Sun, their volatile ices would sublimate, and traditional approaches would classify them as comets and not asteroids.

text: The innermost of these are the Kuiper-belt objects, called "objects" partly to avoid the need to classify them as asteroids or comets.[28] They are thought to be predominantly comet-like in composition, though some may be more akin to asteroids.[29] Furthermore, most do not have the highly eccentric orbits associated with comets, and the ones so far discovered are larger than traditional comet nuclei. (The much more distant Oort cloud is hypothesized to be the main reservoir of dormant comets.) Other recent observations, such as the analysis of the cometary dust collected by the Stardust probe, are increasingly blurring the distinction between comets and asteroids,[30] suggesting "a continuum between asteroids and comets" rather than a sharp dividing line.[31]

text: The minor planets beyond Jupiter's orbit are sometimes also called "asteroids", especially in popular presentations.[note 5] However, it is becoming increasingly common for the term "asteroid" to be restricted to minor planets of the inner Solar System.[28] Therefore, this article will restrict itself for the most part to the classical asteroids: objects of the asteroid belt, Jupiter trojans, and near-Earth objects.

text: When the IAU introduced the class small Solar System bodies in 2006 to include most objects previously classified as minor planets and comets, they created the class of dwarf planets for the largest minor planets—those that have enough mass to have become ellipsoidal under their own gravity. According to the IAU, "the term 'minor planet' may still be used, but generally the term 'Small Solar System Body' will be preferred."[32] Currently only the largest object in the asteroid belt, Ceres, at about 975 km (606 mi) across, has been placed in the dwarf planet category.

text: Formation[edit]

text: It is thought that planetesimals in the asteroid belt evolved much like the rest of the solar nebula until Jupiter neared its current mass, at which point excitation from orbital resonances with Jupiter ejected over 99% of planetesimals in the belt. Simulations and a discontinuity in spin rate and spectral properties suggest that asteroids larger than approximately 120 km (75 mi) in diameter accreted during that early era, whereas smaller bodies are fragments from collisions between asteroids during or after the Jovian disruption.[34] Ceres and Vesta grew large enough to melt and differentiate, with heavy metallic elements sinking to the core, leaving rocky minerals in the crust.[35]

text: In the Nice model, many Kuiper-belt objects are captured in the outer asteroid belt, at distances greater than 2.6 AU. Most were later ejected by Jupiter, but those that remained may be the D-type asteroids, and possibly include Ceres.[36]

text: Distribution within the Solar System[edit]

text: Various dynamical groups of asteroids have been discovered orbiting in the inner Solar System. Their orbits are perturbed by the gravity of other bodies in the Solar System and by the Yarkovsky effect. Significant populations include:

text: Asteroid belt[edit]

text: The majority of known asteroids orbit within the asteroid belt between the orbits of Mars and Jupiter, generally in relatively low-eccentricity (i.e. not very elongated) orbits. This belt is now estimated to contain between 1.1 and 1.9 million asteroids larger than 1 km (0.6 mi) in diameter,[37] and millions of smaller ones. These asteroids may be remnants of the protoplanetary disk, and in this region the accretion of planetesimals into planets during the formative period of the Solar System was prevented by large gravitational perturbations by Jupiter.

text: Trojans[edit]

text: Trojans are populations that share an orbit with a larger planet or moon, but do not collide with it because they orbit in one of the two Lagrangian points of stability, L4 and L5, which lie 60° ahead of and behind the larger body.

text: The most significant population of trojans are the Jupiter trojans. Although fewer Jupiter trojans have been discovered (As of 2010[update]), it is thought that they are as numerous as the asteroids in the asteroid belt. Trojans have been found in the orbits of other planets, including Venus, Earth, Mars, Uranus, and Neptune.

text: Near-Earth asteroids[edit]

text: Near-Earth asteroids, or NEAs, are asteroids that have orbits that pass close to that of Earth. Asteroids that actually cross Earth's orbital path are known as Earth-crossers. As of June 2016[update], 14,464 near-Earth asteroids are known[17] and the number over one kilometer in diameter is estimated to be 900–1,000.

text: Characteristics[edit]

text: Size distribution[edit]

text: Asteroids vary greatly in size, from almost 7006100000000000000♠1000 km for the largest down to rocks just 1 meter across.[note 6] The three largest are very much like miniature planets: they are roughly spherical, have at least partly differentiated interiors,[38] and are thought to be surviving protoplanets. The vast majority, however, are much smaller and are irregularly shaped; they are thought to be either surviving planetesimals or fragments of larger bodies.

text: The dwarf planet Ceres is by far the largest asteroid, with a diameter of 975 km (606 mi). The next largest are 4 Vesta and 2 Pallas, both with diameters of just over 500 km (300 mi). Vesta is the only main-belt asteroid that can, on occasion, be visible to the naked eye. On some rare occasions, a near-Earth asteroid may briefly become visible without technical aid; see 99942 Apophis.

text: The mass of all the objects of the asteroid belt, lying between the orbits of Mars and Jupiter, is estimated to be about 2.8–7021320000000000000♠3.2×1021 kg, or about 4% of the mass of the Moon. Of this, Ceres comprises 7020950000000000000♠0.95×1021 kg, a third of the total.[39] Adding in the next three most massive objects, Vesta (9%), Pallas (7%), and Hygiea (3%), brings this figure up to 51%; whereas the three after that, 511 Davida (1.2%), 704 Interamnia (1.0%), and 52 Europa (0.9%), only add another 3% to the total mass. The number of asteroids then increases rapidly as their individual masses decrease.

text: The number of asteroids decreases markedly with size. Although this generally follows a power law, there are 'bumps' at 7003500000000000000♠5 km and 7005100000000000000♠100 km, where more asteroids than expected from a logarithmic distribution are found.[40]

text:
Approximate number of asteroids (N) larger than a certain diameter (D)

D
0.1 km
0.3 km
0.5 km
1 km
3 km
5 km
10 km
30 km
50 km
100 km
200 km
300 km
500 km
900 km

N
7007250000000000000♠25000000
7006400000000000000♠4000000
7006200000000000000♠2000000
7005750000000000000♠750000
7005200000000000000♠200000
7004900000000000000♠90000
7004100000000000000♠10000
7003110000000000000♠1100
600
200
30
5
3
1

text: Largest asteroids[edit]

text:
1 Ceres
  4 Vesta
  2 Pallas
  10 Hygiea
  31 Euphrosyne
  704 Interamnia
  511 Davida
  532 Herculina
  15 Eunomia
  3 Juno
  16 Psyche
  52 Europa
  all others

text: Although their location in the asteroid belt excludes them from planet status, the three largest objects, Ceres, Vesta, and Pallas, are intact protoplanets that share many characteristics common to planets, and are atypical compared to the majority of "potato"-shaped asteroids. The fourth largest asteroid, Hygiea, has an undifferentiated interior, like the majority of asteroids. Between them, the four largest asteroids constitute half the mass of the asteroid belt.

text: Ceres is the only asteroid with a fully ellipsoidal shape and hence the only one that is a dwarf planet.[24] It has a much higher absolute magnitude than the other asteroids, of around 3.32,[43] and may possess a surface layer of ice.[44] Like the planets, Ceres is differentiated: it has a crust, a mantle and a core.[44] No meteorites from Ceres have been found on Earth.

text: Vesta, too, has a differentiated interior, though it formed inside the Solar System's frost line, and so is devoid of water;[45][46] its composition is mainly of basaltic rock such as olivine.[47] Aside from the large crater at its southern pole, Rheasilvia, Vesta also has an ellipsoidal shape. Vesta is the parent body of the Vestian family and other V-type asteroids, and is the source of the HED meteorites, which constitute 5% of all meteorites on Earth.

text: Pallas is unusual in that, like Uranus, it rotates on its side, with its axis of rotation tilted at high angles to its orbital plane.[48] Its composition is similar to that of Ceres: high in carbon and silicon, and perhaps partially differentiated.[49] Pallas is the parent body of the Palladian family of asteroids.

text: Hygiea is the largest carbonaceous asteroid[50] and, unlike the other largest asteroids, lies relatively close to the plane of the ecliptic.[51] It is the largest member and presumed parent body of the Hygiean family of asteroids.

text:
Attributes of largest asteroids

Name
Orbital
radius
(AU)
Orbital
period
(years)
Inclination
to ecliptic
Orbital
eccentricity
Diameter
(km)
Diameter
(% of Moon)
Mass
(×1018 kg)
Mass
(% of Ceres)
Density[52]
(g/cm3)
Rotation
period
(hr)
Axial tilt
Surface
temperature

Vesta
2.36
3.63
7.1°
0.089
573×557×446
(mean 525)
15%
260
28%
3.44 ± 0.12
5.34
29°
85–270 K

Ceres
2.77
4.60
10.6°
0.079
975×975×909
(mean 953)
28%
940
100%
2.12 ± 0.04
9.07
≈ 3°
167 K

Pallas
2.77
4.62
34.8°
0.231
580×555×500
(mean 545)
16%
210
22%
2.71 ± 0.11
7.81
≈ 80°
164 K

Hygiea
3.14
5.56
3.8°
0.117
530×407×370
(mean 435)
12%
87
9%
2.76 ± 1.2
27.6
≈ 60°
164 K

text: Rotation[edit]

text: Measurements of the rotation rates of large asteroids in the asteroid belt show that there is an upper limit. No asteroid with a diameter larger than 100 meters has a rotation period smaller than 2.2 hours. For asteroids rotating faster than approximately this rate, the inertial force at the surface is greater than the gravitational force, so any loose surface material would be flung out. However, a solid object should be able to rotate much more rapidly. This suggests that most asteroids with a diameter over 100 meters are rubble piles formed through accumulation of debris after collisions between asteroids.[53]

text: Composition[edit]

text: The physical composition of asteroids is varied and in most cases poorly understood. Ceres appears to be composed of a rocky core covered by an icy mantle, where Vesta is thought to have a nickel-iron core, olivine mantle, and basaltic crust.[54] 10 Hygiea, however, which appears to have a uniformly primitive composition of carbonaceous chondrite, is thought to be the largest undifferentiated asteroid. Most of the smaller asteroids are thought to be piles of rubble held together loosely by gravity, though the largest are probably solid. Some asteroids have moons or are co-orbiting binaries: Rubble piles, moons, binaries, and scattered asteroid families are thought to be the results of collisions that disrupted a parent asteroid, or, possibly, a planet.[55]

text: Asteroids contain traces of amino acids and other organic compounds, and some speculate that asteroid impacts may have seeded the early Earth with the chemicals necessary to initiate life, or may have even brought life itself to Earth (also see panspermia).[56] In August 2011, a report, based on NASA studies with meteorites found on Earth, was published suggesting DNA and RNA components (adenine, guanine and related organic molecules) may have been formed on asteroids and comets in outer space.[57][58][59]

text: Composition is calculated from three primary sources: albedo, surface spectrum, and density. The last can only be determined accurately by observing the orbits of moons the asteroid might have. So far, every asteroid with moons has turned out to be a rubble pile, a loose conglomeration of rock and metal that may be half empty space by volume. The investigated asteroids are as large as 280 km in diameter, and include 121 Hermione (268×186×183 km), and 87 Sylvia (384×262×232 km). Only half a dozen asteroids are larger than 87 Sylvia, though none of them have moons; however, some smaller asteroids are thought to be more massive, suggesting they may not have been disrupted, and indeed 511 Davida, the same size as Sylvia to within measurement error, is estimated to be two and a half times as massive, though this is highly uncertain. The fact that such large asteroids as Sylvia can be rubble piles, presumably due to disruptive impacts, has important consequences for the formation of the Solar System: Computer simulations of collisions involving solid bodies show them destroying each other as often as merging, but colliding rubble piles are more likely to merge. This means that the cores of the planets could have formed relatively quickly.[60]

text: On 7 October 2009, the presence of water ice was confirmed on the surface of 24 Themis using NASA’s Infrared Telescope Facility. The surface of the asteroid appears completely covered in ice. As this ice layer is sublimated, it may be getting replenished by a reservoir of ice under the surface. Organic compounds were also detected on the surface.[61][62][63][64] Scientists hypothesize that some of the first water brought to Earth was delivered by asteroid impacts after the collision that produced the Moon. The presence of ice on 24 Themis supports this theory.[63]

text: In October 2013, water was detected on an extrasolar body for the first time, on an asteroid orbiting the white dwarf GD 61.[65] On 22 January 2014, European Space Agency (ESA) scientists reported the detection, for the first definitive time, of water vapor on Ceres, the largest object in the asteroid belt.[66] The detection was made by using the far-infrared abilities of the Herschel Space Observatory.[67] The finding is unexpected because comets, not asteroids, are typically considered to "sprout jets and plumes". According to one of the scientists, "The lines are becoming more and more blurred between comets and asteroids."[67] In May 2016, significant asteroid data arising from the Wide-field Infrared Survey Explorer and NEOWISE missions have been questioned.[68][69][70] Although the early original criticism had not undergone peer review,[71] a more recent peer-reviewed study was subsequently published.[72][73]

text: Surface features[edit]

text: Most asteroids outside the "big four" (Ceres, Pallas, Vesta, and Hygiea) are likely to be broadly similar in appearance, if irregular in shape. 50-km (31-mi) 253 Mathilde is a rubble pile saturated with craters with diameters the size of the asteroid's radius, and Earth-based observations of 300-km (186-mi) 511 Davida, one of the largest asteroids after the big four, reveal a similarly angular profile, suggesting it is also saturated with radius-size craters.[74] Medium-sized asteroids such as Mathilde and 243 Ida that have been observed up close also reveal a deep regolith covering the surface. Of the big four, Pallas and Hygiea are practically unknown. Vesta has compression fractures encircling a radius-size crater at its south pole but is otherwise a spheroid. Ceres seems quite different in the glimpses Hubble has provided, with surface features that are unlikely to be due to simple craters and impact basins, but details will be expanded with the Dawn spacecraft, which entered Ceres orbit on 6 March 2015.[75]

text: Color[edit]

text: Asteroids become darker and redder with age due to space weathering.[76] However evidence suggests most of the color change occurs rapidly, in the first hundred thousands years, limiting the usefulness of spectral measurement for determining the age of asteroids.[77]

text: Classification[edit]

text: Asteroids are commonly classified according to two criteria: the characteristics of their orbits, and features of their reflectance spectrum.

text: Orbital classification[edit]

text: Many asteroids have been placed in groups and families based on their orbital characteristics. Apart from the broadest divisions, it is customary to name a group of asteroids after the first member of that group to be discovered. Groups are relatively loose dynamical associations, whereas families are tighter and result from the catastrophic break-up of a large parent asteroid sometime in the past.[78] Families are more common and easier to identify within the main asteroid belt, but several small families have been reported among the Jupiter trojans.[79] Main belt families were first recognized by Kiyotsugu Hirayama in 1918 and are often called Hirayama families in his honor.

text: About 30–35% of the bodies in the asteroid belt belong to dynamical families each thought to have a common origin in a past collision between asteroids. A family has also been associated with the plutoid dwarf planet Haumea.

text: Quasi-satellites and horseshoe objects[edit]

text: Some asteroids have unusual horseshoe orbits that are co-orbital with Earth or some other planet. Examples are 3753 Cruithne and 2002 AA29. The first instance of this type of orbital arrangement was discovered between Saturn's moons Epimetheus and Janus.

text: Sometimes these horseshoe objects temporarily become quasi-satellites for a few decades or a few hundred years, before returning to their earlier status. Both Earth and Venus are known to have quasi-satellites.

text: Such objects, if associated with Earth or Venus or even hypothetically Mercury, are a special class of Aten asteroids. However, such objects could be associated with outer planets as well.

text: Spectral classification[edit]

text: In 1975, an asteroid taxonomic system based on color, albedo, and spectral shape was developed by Clark R. Chapman, David Morrison, and Ben Zellner.[80] These properties are thought to correspond to the composition of the asteroid's surface material. The original classification system had three categories: C-types for dark carbonaceous objects (75% of known asteroids), S-types for stony (silicaceous) objects (17% of known asteroids) and U for those that did not fit into either C or S. This classification has since been expanded to include many other asteroid types. The number of types continues to grow as more asteroids are studied.

text: The two most widely used taxonomies now used are the Tholen classification and SMASS classification. The former was proposed in 1984 by David J. Tholen, and was based on data collected from an eight-color asteroid survey performed in the 1980s. This resulted in 14 asteroid categories.[81] In 2002, the Small Main-Belt Asteroid Spectroscopic Survey resulted in a modified version of the Tholen taxonomy with 24 different types. Both systems have three broad categories of C, S, and X asteroids, where X consists of mostly metallic asteroids, such as the M-type. There are also several smaller classes.[82]

text: The proportion of known asteroids falling into the various spectral types does not necessarily reflect the proportion of all asteroids that are of that type; some types are easier to detect than others, biasing the totals.

text:
Summary of asteroid taxonomic classes

Tholen Class
SMASSII
(Bus Class)

Albedo
Spectral Features

A
A
moderate
Very steep red slope shortward of 0.75 µm; moderately deep
absorption feature longward of 0.75 µm.

B, C, F, G
B, C, Cb, Ch, Cg, Chg
low
Linear, generally featureless spectra. Differences in UV absorption features and presence/absence of narrow absorption feature near 0.7 µm.

D
D
low
Relatively featureless spectrum with very steep red slope.

E, M, P
X, Xc, Xe, Xk
from low (P)
to very high (E)

Generally featureless spectrum with reddish slope; differences in subtle absorption features and/or spectral curvature and/or peak relative reflectance.

Q
Q
moderate
Reddish slope shortward of 0.7 µm; deep, rounded absorption feature longward of 0.75 µm.

R
R
moderate
Moderate reddish slope downward of 0.7 µm; deep absorption longward of 0.75 µm.

S
S, Sa, Sk, Sl, Sq, Sr
moderate
Moderately steep reddish slope downward of 0.7 µm; moderate to steep absorption longward of 0.75 µm; peak of reflectance at 0.73 µm. Bus subgroups intermediate between S and A, K, L, Q, R classes.

T
T
low
Moderately reddish shortward of 0.75 µm; flat afterward.

V
V
moderate
Reddish shortward of 0.7 µm; extremely deep absorption longward of 0.75 µm.

—
K
moderate
Moderately steep red slope shortward of 0.75 µm; smoothly angled maximum and flat to blueish longward of 0.75 µm, with little or no curvature.

—
L, Ld
moderate
Very steep red slope shortward of 0.75 µm; flat longward of 0.75 µm; differences in peak level.

—
O
—
Peculiar trend, known so far only for asteroid 3628.

text: Problems[edit]

text: Originally, spectral designations were based on inferences of an asteroid's composition.[83] However, the correspondence between spectral class and composition is not always very good, and a variety of classifications are in use. This has led to significant confusion. Although asteroids of different spectral classifications are likely to be composed of different materials, there are no assurances that asteroids within the same taxonomic class are composed of similar materials.

text: Naming[edit]

text: A newly discovered asteroid is given a provisional designation (such as 2002 AT4) consisting of the year of discovery and an alphanumeric code indicating the half-month of discovery and the sequence within that half-month. Once an asteroid's orbit has been confirmed, it is given a number, and later may also be given a name (e.g. 433 Eros). The formal naming convention uses parentheses around the number (e.g. (433) Eros), but dropping the parentheses is quite common. Informally, it is common to drop the number altogether, or to drop it after the first mention when a name is repeated in running text.[84] In addition, names can be proposed by the asteroid's discoverer, within guidelines established by the International Astronomical Union.[85]

text: Symbols[edit]

text: The first asteroids to be discovered were assigned iconic symbols like the ones traditionally used to designate the planets. By 1855 there were two dozen asteroid symbols, which often occurred in multiple variants.[86]

text:
Asteroid
Symbol
Year

1 Ceres
⚳
Ceres' scythe, reversed to double as the letter C
1801

2 Pallas
⚴
Athena's (Pallas') spear
1801

3 Juno
⚵
A star mounted on a scepter, for Juno, the Queen of Heaven
1804

4 Vesta
⚶
The altar and sacred fire of Vesta
1807

5 Astraea

A scale, or an inverted anchor, symbols of justice
1845

6 Hebe

Hebe's cup
1847

7 Iris

A rainbow (iris) and a star
1847

8 Flora

A flower (flora), specifically the Rose of England
1847

9 Metis

The eye of wisdom and a star
1848

10 Hygiea

Hygiea's serpent and a star, or the Rod of Asclepius
1849

11 Parthenope

A harp, or a fish and a star; symbols of the sirens
1850

12 Victoria

The laurels of victory and a star
1850

13 Egeria

A shield, symbol of Egeria's protection, and a star
1850

14 Irene

A dove carrying an olive branch (symbol of irene 'peace')
with a star on its head,[87] or an olive branch, a flag of truce, and a star
1851

15 Eunomia

A heart, symbol of good order (eunomia), and a star
1851

16 Psyche

A butterfly's wing, symbol of the soul (psyche), and a star
1852

17 Thetis

A dolphin, symbol of Thetis, and a star
1852

18 Melpomene

The dagger of Melpomene, and a star
1852

19 Fortuna

The wheel of fortune and a star
1852

26 Proserpina

Proserpina's pomegranate
1853

28 Bellona

Bellona's whip and lance[88]
1854

29 Amphitrite

The shell of Amphitrite and a star
1854

35 Leukothea

A lighthouse beacon, symbol of Leucothea[89]
1855

37 Fides

The cross of faith (fides)[90]
1855

text: In 1851,[91] after the fifteenth asteroid (Eunomia) had been discovered, Johann Franz Encke made a major change in the upcoming 1854 edition of the Berliner Astronomisches Jahrbuch (BAJ, Berlin Astronomical Yearbook). He introduced a disk (circle), a traditional symbol for a star, as the generic symbol for an asteroid. The circle was then numbered in order of discovery to indicate a specific asteroid (although he assigned ① to the fifth, Astraea, while continuing to designate the first four only with their existing iconic symbols). The numbered-circle convention was quickly adopted by astronomers, and the next asteroid to be discovered (16 Psyche, in 1852) was the first to be designated in that way at the time of its discovery. However, Psyche was given an iconic symbol as well, as were a few other asteroids discovered over the next few years (see chart above). 20 Massalia was the first asteroid that was not assigned an iconic symbol, and no iconic symbols were created after the 1855 discovery of 37 Fides.[note 8] That year Astraea's number was increased to ⑤, but the first four asteroids, Ceres to Vesta, were not listed by their numbers until the 1867 edition. The circle was soon abbreviated to a pair of parentheses, which were easier to typeset and sometimes omitted altogether over the next few decades, leading to the modern convention.[87]

text: Exploration[edit]

text: Until the age of space travel, objects in the asteroid belt were merely pinpricks of light in even the largest telescopes and their shapes and terrain remained a mystery. The best modern ground-based telescopes and the Earth-orbiting Hubble Space Telescope can resolve a small amount of detail on the surfaces of the largest asteroids, but even these mostly remain little more than fuzzy blobs. Limited information about the shapes and compositions of asteroids can be inferred from their light curves (their variation in brightness as they rotate) and their spectral properties, and asteroid sizes can be estimated by timing the lengths of star occulations (when an asteroid passes directly in front of a star). Radar imaging can yield good information about asteroid shapes and orbital and rotational parameters, especially for near-Earth asteroids. In terms of delta-v and propellant requirements, NEOs are more easily accessible than the Moon.[92]

text: The first close-up photographs of asteroid-like objects were taken in 1971, when the Mariner 9 probe imaged Phobos and Deimos, the two small moons of Mars, which are probably captured asteroids. These images revealed the irregular, potato-like shapes of most asteroids, as did later images from the Voyager probes of the small moons of the gas giants.

text: The first true asteroid to be photographed in close-up was 951 Gaspra in 1991, followed in 1993 by 243 Ida and its moon Dactyl, all of which were imaged by the Galileo probe en route to Jupiter.

text: The first dedicated asteroid probe was NEAR Shoemaker, which photographed 253 Mathilde in 1997, before entering into orbit around 433 Eros, finally landing on its surface in 2001.

text: Other asteroids briefly visited by spacecraft en route to other destinations include 9969 Braille (by Deep Space 1 in 1999), and 5535 Annefrank (by Stardust in 2002).

text: In September 2005, the Japanese Hayabusa probe started studying 25143 Itokawa in detail and was plagued with difficulties, but returned samples of its surface to Earth on 13 June 2010.

text: The European Rosetta probe (launched in 2004) flew by 2867 Šteins in 2008 and 21 Lutetia, the third-largest asteroid visited to date, in 2010.

text: In September 2007, NASA launched the Dawn spacecraft, which orbited 4 Vesta from July 2011 to September 2012, and has been orbiting the dwarf planet 1 Ceres since 2015. 4 Vesta is the second-largest asteroid visited to date.

text: On 13 December 2012, China's lunar orbiter Chang'e 2 flew within 3.2 km (2 mi) of the asteroid 4179 Toutatis on an extended mission.

text: Planned and future missions[edit]

text: The Japan Aerospace Exploration Agency (JAXA) launched the Hayabusa2 probe in December 2014, and plans to return samples from 162173 Ryugu in December 2020.

text: In May 2011, NASA selected the OSIRIS-REx sample return mission to asteroid 101955 Bennu; it launched on September 8, 2016.

text: In early 2013, NASA announced the planning stages of a mission to capture a near-Earth asteroid and move it into lunar orbit where it could possibly be visited by astronauts and later impacted into the Moon.[93] On 19 June 2014, NASA reported that asteroid 2011 MD was a prime candidate for capture by a robotic mission, perhaps in the early 2020s.[94]

text: It has been suggested that asteroids might be used as a source of materials that may be rare or exhausted on Earth (asteroid mining), or materials for constructing space habitats (see Colonization of the asteroids). Materials that are heavy and expensive to launch from Earth may someday be mined from asteroids and used for space manufacturing and construction.

text: In the U.S. Discovery program the Psyche spacecraft proposal to 16 Psyche and Lucy spacecraft to Jupiter trojans made it to the semifinalist stage of mission selection.

text: Fiction[edit]

text: Asteroids and the asteroid belt are a staple of science fiction stories. Asteroids play several potential roles in science fiction: as places human beings might colonize, resources for extracting minerals, hazards encountered by spacecraft traveling between two other points, and as a threat to life on Earth or other inhabited planets, dwarf planets and natural satellites by potential impact.

text: Gallery[edit]

text:
951 Gaspra is the first asteroid to be imaged in close-up, imaged by Galileo on 29 October 1991 (enhanced color)

Several views of 433 Eros in natural color, imaged by NEAR on 12 February 2000

Vesta imaged by Dawn on 9 July 2011

Ceres imaged by Dawn on 4 February 2015


document_title: List of highest individual scores in ODIs

question_text: rohit sharma highest score in one day 264

text: One Day International (ODI) cricket is played between international cricket teams who are Full Members of the International Cricket Council (ICC) as well as the top six Associate and Affiliate members.[1] Unlike Test matches, ODIs consist of one innings per team, having a limit in the number of overs.

text: The limit of overs is currently 50 overs per innings, although in the past this has been 55 or 60 overs.[2] ODI cricket is List-A cricket, so statistics and records set in ODI matches also count toward List-A records. The earliest match now recognized as an ODI was played between England and Australia in January 1971;[3] since then there have been over 3,000 ODIs played by 26 teams. The frequency of matches has steadily increased, partly because of the increase in the number of ODI-playing countries, and partly as the cricket boards of those nations seek to maximise their revenue.[4]

text: Before breaking the 200 mark, the highest ODI score was 194 jointly held by Pakistani Saeed Anwar and Zimbabwean Charles Coventry. In One Day Internationals, the first man to score a double century was Indian batsman Sachin Tendulkar, who scored 200 not out against South Africa at Captain Roop Singh Stadium in Gwalior, India. Rohit Sharma is the only player in history to score 3 double centuries.[5] The following table lists scores of 180 or higher.

text: Highest ODI individual scores[edit]

text:
Rank
Name
Score
4s
6s
Strike Rate
Innings
Team
Opponent
Venue
Date
Result

1
Sharma, RohitRohit Sharma
264
33
9
152.60
1
 India
 Sri Lanka
Eden Gardens, Kolkata
13 November 2014
Won[6]

2
Guptill, MartinMartin Guptill
237*
24
11
145.39
1
 New Zealand
 West Indies
Westpac Stadium, Wellington
21 March 2015
Won[7]

3
Sehwag, VirenderVirender Sehwag
219
25
7
146.97
1
 India
 West Indies
Holkar Cricket Stadium, Indore
8 December 2011
Won[8]

4
Gayle, ChrisChris Gayle
215
10
16
146.25
1
 West Indies
 Zimbabwe
Manuka Oval, Canberra
24 February 2015
Won[9]

5
Sharma, RohitRohit Sharma
209
12
16
132.28
1
 India
 Australia
M. Chinnaswamy Stadium, Bangalore
2 November 2013
Won[10]

6
Sharma, RohitRohit Sharma
208*
13
12
135.94
1
 India
 Sri Lanka
PCA IS Bindra Stadium, Mohali
13 December 2017
Won[11]

7
Tendulkar, SachinSachin Tendulkar
200*
25
3
136.05
1
 India
 South Africa
Captain Roop Singh Stadium, Gwalior
24 February 2010
Won[12]

8
Charles Coventry
194*
16
7
124.36
1
 Zimbabwe
 Bangladesh
Queens Sports Club, Bulawayo
16 August 2009
Lost[13]

8
Saeed Anwar
194
22
5
132.88
1
 Pakistan
 India
M. A. Chidambaram Stadium, Chennai
21 May 1997
Won[14]

10
Vivian Richards
189*
21
5
111.18
1
 West Indies
 England
Old Trafford Cricket Ground, Manchester
31 May 1984
Won[15]

10
Martin Guptill
189*
19
2
121.94
1
 New Zealand
 England
Rose Bowl, Southampton
2 June 2013
Won[16]

10
Jayasuriya, SanathSanath Jayasuriya
189
21
4
117.39
1
 Sri Lanka
 India
Sharjah Cricket Association Stadium, Sharjah
29 October 2000
Won[17]

13
Kirsten, GaryGary Kirsten
188*
13
4
118.24
1
 South Africa
 United Arab Emirates
Rawalpindi Cricket Stadium, Rawalpindi
16 February 1996
Won[18]

14
Sachin Tendulkar
186*
20
3
124.00
1
 India
 New Zealand
Lal Bahadur Shastri Stadium, Hyderabad
8 November 1999
Won[19]

15
Watson, ShaneShane Watson
185*
15
15
192.71
2
 Australia
 Bangladesh
Sher-e-Bangla National Cricket Stadium, Dhaka
11 April 2011
Won[20]

15
du Plessis, FafFaf du Plessis
185
16
3
131.20
1
 South Africa
 Sri Lanka
Newlands Cricket Ground, Cape Town
7 February 2017
Won[21]

17
Dhoni, MSMS Dhoni
183*
15
10
126.21
2
 India
 Sri Lanka
Sawai Mansingh Stadium, Jaipur
31 October 2005
Won[22]

17
Ganguly, SouravSourav Ganguly
183
17
7
115.82
1
 India
 Sri Lanka
County Ground, Taunton
26 May 1999
Won[23]

17
Kohli, ViratVirat Kohli
183
22
1
123.65
2
 India
 Pakistan
Sher-e-Bangla National Cricket Stadium, Dhaka
18 March 2012
Won[24]

20
Taylor, RossRoss Taylor
181*
17
6
123.12
2
 New Zealand
 England
University of Otago Oval, Dunedin
7 March 2018
Won[25]

20
Hayden, MatthewMatthew Hayden
181*
11
10
109.03
1
 Australia
 New Zealand
Seddon Park, Hamilton
20 February 2007
Lost[26]

20
Richards, VivViv Richards
181
16
7
144.80
1
 West Indies
 Sri Lanka
National Stadium, Karachi, Karachi
13 October 1987
Won[27]

21
Roy, JasonJason Roy
180
16
5
119.20
2
 England
 Australia
MCG, Melbourne, Melbourne
14 January 2018
Won[28]

text: * indicates not out