document_title: List of tallest players in National Basketball Association history

question_text: who is the tallest player in nba history

text: This is a list of the tallest players in National Basketball Association history. Twenty five of them have been listed at 7 feet, 3 inches or taller. Three are active as of the 2016–17 season; Kristaps Porziņģis of the New York Knicks, Walter Tavares of the Cleveland Cavaliers, and Boban Marjanović of the Detroit Pistons. The tallest player inducted into the Naismith Memorial Basketball Hall of Fame is 7 feet, 6 inch Yao Ming. In addition to Yao, Ralph Sampson and Arvydas Sabonis were the only other players 7'3" or taller selected to the Hall of Fame.

text: In the seventh round of the 1981 NBA Draft, the Golden State Warriors used the 171st pick to select Yasutaka Okayama, a Japanese basketball player who was measured at 7 feet 8 inches (2.34 m) and 330 pounds (150 kg).[1][2] Okayama, who attended and played junior varsity basketball at the University of Portland for one and a half years in 1976 as an exchange student, declined to try out for the Warriors and never played in the NBA.[3] He is the tallest person ever drafted and would have been the tallest player in the NBA had he played in the league.[4]

text:
^
Active NBA player

*
Inducted into the Naismith Memorial Basketball Hall of Fame

GP
Games played
Pts
Points
PPG
Points per game

FG%
Field goal percentage
FT%
Free throw percentage
Reb
Rebounds

RPG
Rebounds per game
Blk
Blocks
BPG
Blocks per game

text:
Height
Weight
Player
Nationality
Teams
GP
Pts
PPG
FG%
FT%
Reb
RPG
Blk
BPG
Notes

7 ft 7 in (2.31 m)
315 lb (143 kg)
Mureșan, GheorgheGheorghe Mureșan
 ROU
Washington Bullets (1993–1997)
New Jersey Nets (1998–2000)
307
3,020
9.8
.573
.644
1,957
6.4
455
1.5
Generally considered slightly taller than Manute Bol. Bol was officially measured at 7 feet, 6 3/4 inches tall by the Guinness Book of World Records.

7 ft 6.75 in (2.31 m)
200 lb (91 kg)
Bol, ManuteManute Bol
 SUD
Washington Bullets (1985–1988, 1994)
Golden State Warriors (1988–1990, 1994)
Philadelphia 76ers (1990–1993, 1994)
Miami Heat (1994)
624
1,599
2.6
.407
.561
2,647
4.2
2,086
3.3
Played alongside the shortest player in NBA history, Muggsy Bogues, during the 1987–88 season for the Washington Bullets; their difference in height was 28 inches. Only player in NBA history to have more blocked shots than points scored in his career. Weighed just 195 pounds (89 kg)[citation needed] when he entered the league in 1985.

7 ft 6 in (2.29 m)
275 lb (125 kg)
Bradley, ShawnShawn Bradley
 USA
 GER
Philadelphia 76ers (1993–1995)
New Jersey Nets (1995–1997)
Dallas Mavericks (1997–2005)
832
6,752
8.1
.457
.716
5,268
6.3
2,119
2.5
Born to American parents in the former West Germany.

7 ft 6 in (2.29 m)
310 lb (141 kg)
Yao Ming, Yao Ming*
 CHN
Houston Rockets (2002–2011)
481
9,196
19.1
.525
.832
4,467
9.3
912
1.9
Tallest player to play in at least one All-Star Game. Also tallest player inducted into the Hall of Fame.

7 ft 5 in (2.26 m)
359 lb (163 kg)
Bhullar, SimSim Bhullar
 CAN
Sacramento Kings (2015)
3
2
0.7
.500
—
1
0.3
1
0.3
First NBA player of Indian descent. Played 16 seconds in his debut on April 7, 2015.

7 ft 5 in (2.26 m)
250 lb (113 kg)
Nevitt, ChuckChuck Nevitt
 USA
Houston Rockets (1982–1983, 1988–1990)
Los Angeles Lakers (1984–1985)
Detroit Pistons (1985–1988)
Chicago Bulls (1991)
San Antonio Spurs (1993)
155
251
1.6
.438
.589
239
1.5
111
0.7
Tallest player to win an NBA Championship.

7 ft 5 in (2.26 m)
305 lb (138 kg)
Podkolzin, PavelPavel Podkolzin
 RUS
Dallas Mavericks (2004–2006)
6
4
0.7
.000
.500
9
1.5
1
0.1

7 ft 5 in (2.26 m)
294 lb (133 kg)
Vraneš, SlavkoSlavko Vraneš
 MNE
Portland Trail Blazers (2004)
1
0
0.0
.000
—
0
0.0
0
0.0
Played in one game, on 000000002004-01-08-0000January 8, 2004 against the Minnesota Timberwolves. Played 3 minutes, with one shot attempt from the field (missed) and one personal foul. Vraneš was officially listed as 7'5" while playing in the NBA, and has since grown taller (7'6" or 2.30 m), according to most sources.

7 ft 4 in (2.24 m)
290 lb (132 kg)
Eaton, MarkMark Eaton
 USA
Utah Jazz (1982–1993)
875
5,216
6.0
.458
.649
6,939
7.9
3,064
3.5
He set records for most blocked shots per game in a single season (5.56 bpg in 1984–85) and for an entire career (3.50 bpg) - both marks still stand today.

7 ft 4 in (2.24 m)
250 lb (113 kg)
Smits, RikRik Smits
 NED
Indiana Pacers (1988–2000)
867
12,871
14.8
.507
.773
5,277
6.1
1,111
1.3

7 ft 4 in (2.24 m)
235 lb (107 kg)
Sampson, RalphRalph Sampson*
 USA
Houston Rockets (1983–1987)
Golden State Warriors (1987–1989)
Sacramento Kings (1989–1991)
Washington Bullets (1991–1992)
456
7,039
15.4
.486
.661
4,011
8.8
752
1.6

7 ft 4 in (2.24 m)
325 lb (147 kg)
Lauderdale, PriestPriest Lauderdale
 USA
Atlanta Hawks (1996–1997)
Denver Nuggets (1997–1998)
74
255
3.4
.472
.554
143
1.9
26
0.4

7 ft 3.5 in (2.22 m)
293 lb (133 kg)
Marjanović, BobanBoban Marjanović^
 SER
San Antonio Spurs (2015–2016)
Detroit Pistons (2016–present)
89
488
5.5
.578
.779
324
3.6
35
0.4

7 ft 3.5 in (2.22 m)
290 lb (132 kg)
Ramos, Peter JohnPeter John Ramos
 PUR
Washington Wizards (2004–2005)
6
11
1.8
.500
.500
4
0.7
1
0.2

7 ft 3 in (2.21 m)
263 lb (119 kg)
Breuer, RandyRandy Breuer
 USA
Milwaukee Bucks (1983–1990)
Minnesota Timberwolves (1990–1992)
Atlanta Hawks (1992–1993)
Sacramento Kings (1993)
681
4,599
6.8
.467
.628
2,986
4.4
750
1.1

7 ft 3 in (2.21 m)
212 lb (96 kg)
Closs, KeithKeith Closs
 USA
Los Angeles Clippers (1997–2000)
130
502
3.9
.471
.606
372
2.9
163
1.3
During his collegiate career, Closs averaged 5.9 blocks per game, which is the NCAA Division I record.

7 ft 3 in (2.21 m)
235 lb (107 kg)
Halbrook, SwedeSwede Halbrook
 USA
Syracuse Nationals (1960–1962)
143
786
5.5
.347
.591
949
6.6
—
—

7 ft 3 in (2.21 m)
260 lb (118 kg)
Ilgauskas, ŽydrūnasŽydrūnas Ilgauskas
 LTU
Cleveland Cavaliers (1997–2010)
Miami Heat (2010–2011)
771
10,616
13.8
.475
.780
5,904
7.7
1,269
1.6

7 ft 3 in (2.21 m)
250 lb (113 kg)
Radojević, AleksandarAleksandar Radojević
 BIH
 MNE
Toronto Raptors (1999–2000)
Utah Jazz (2004–2005)
15
26
1.7
.308
.625
36
2.4
3
0.2

7 ft 3 in (2.21 m)
292 lb (132 kg)
Sabonis, ArvydasArvydas Sabonis*
 LTU
Portland Trail Blazers (1995–2001, 2002–2003)
470
5,629
12.0
.500
.786
3,436
7.3
494
1.1
Sabonis was originally drafted into the NBA in 1986 (Rd. 1, #24 overall), but he was not allowed to play in the NBA for most of his career due to restrictions by the former Soviet Union.

7 ft 3 in (2.21 m)
305 lb (138 kg)
Seung-Jin, HaHa Seung-Jin
 KOR
Portland Trail Blazers (2005–2006)
46
70
1.5
.519
.500
67
1.5
13
0.3
Only Korean player to play in the NBA.

7 ft 3 in (2.21 m)
290 lb (132 kg)
Thabeet, HasheemHasheem Thabeet^
 TZA
Memphis Grizzlies (2009–2011)
Houston Rockets (2011–2012)
Portland Trail Blazers (2012)
Oklahoma City Thunder (2012–2014)
224
483
2.2
.567
.578
595
2.7
184
0.8
Only Tanzanian player to play in the NBA.

7 ft 3 in (2.21 m)
256 lb (116 kg)
Pleiß, TiborTibor Pleiß
 GER
Utah Jazz (2015–2016)
12
24
2.0
.440
1.000
15
1.3
2
0.2

7 ft 3 in (2.21 m)
265 lb (120 kg)
Tavares, WalterWalter Tavares^
 CPV
Atlanta Hawks (2015–2016)
Cleveland Cavaliers (2017–Present)
13
33
2.5
.625
.273
32
2.5
12
0.9
Only Cape Verdean player to play in the NBA.

7 ft 3 in (2.21 m)
240 lb (109 kg)
Porziņģis, KristapsKristaps Porziņģis^
 LAT
New York Knicks (2015–Present)
138
2,224
16.1
.436
.811
1001
7.3
263
1.9
Was measured at 7'1" during the NBA Draft Combine, but grew two inches before officially playing for the New York Knicks. Is the tallest winner of the Taco Bell Skills Challenge.


document_title: Geography of Halloween

question_text: when did halloween catch on in this country

root

text: Geography of Halloween

text: Origins[edit]

text: Halloween, also spelled as Hallowe'en or Allhallowe'en, is a contraction of All Hallows' Eve, the eve or vigil before the Western Christian feast of All Hallows (or All Saints) which is observed on 1 November. This day begins the triduum of Hallowtide, which culminates with All Souls' Day. In the Middle Ages, many Christians held a folk belief that All Hallows' Eve was the "night where the veil between the material world and the afterlife was at its most transparent."[2]

tag: p

text: Asia[edit]

text: China[edit]

text: The Chinese celebrate the "Hungry Ghost Festival" in mid-July, when it is customary to float river lanterns to remember those who have died. By contrast, Halloween is often (erroneously) called "All Saints' Day" (Wànshèngjié, 萬聖節), or (less commonly, but more correctly) "All Saints' Eve" (Wànshèngyè, 萬聖夜) or "Eve of All Saints' Day" (Wànshèngjié Qiányè, 萬聖節前夕). Chinese Christian churches hold religious celebrations. Non-religious celebrations are dominated by expatriate Americans or Canadians, but costume parties are also popular for Chinese young adults, especially in large cities. Hong Kong Disneyland and Ocean Park (Halloween Bash) host annual Halloween shows.

text: Mainland China has been less influenced by Anglo traditions than Hong Kong and Halloween is generally considered "foreign." As Halloween has become more popular globally it has also become more popular in China, however, particularly amongst children attending private or international schools with many foreign teachers from North America.[3]

text: Hong Kong[edit]

text: Traditional "door-to-door" trick or treating is not commonly practiced in Hong Kong due to the vast majority of Hong Kong residents living in high-rise apartment blocks. However, in many buildings catering to expatriates, Halloween parties and limited trick or treating is arranged by the management. Instances of street-level trick or treating in Hong Kong occur in ultra-exclusive gated housing communities such as The Beverly Hills populated by Hong Kong's super-rich and in expatriate areas like Discovery Bay and the Red Hill Peninsula. For the general public, there are events at Tsim Sha Tsui's Avenue of the Stars that try to mimic the celebration.[4] In the Lan Kwai Fong area of Hong Kong, known as a major entertainment district for the international community, a Halloween celebration and parade has taken place for over 20 years, with many people dressing in costume and making their way around the streets to various drinking establishments.[5] Many international schools also celebrate Halloween with costumes, and some put an academic twist on the celebrations such as the "Book-o-ween" celebrations at Hong Kong International School where students dress as favorite literary characters.

text: Japan[edit]

text: Halloween arrived in Japan mainly as a result of American pop culture. As recently as 2009, it was not appreciated and only celebrated by expats.[6] The wearing of elaborate costumes by young adults night is recently very popular in areas such as Amerikamura in Osaka and Shibuya in Tokyo, where, in October 2012, about 1700 people dressed in costumes to take part in the Halloween Festival.[7] The holiday has become popular with young adults as a costume party and club event.[8] Trick or Treating for Japanese children has taken hold in some areas. The Yakuza have taken advantage of the festival by hosting parties and giving snacks and sweets to children, a tradition which goes back at least for 20 years.[9]

text: Philippines[edit]

text: The period from 31 October through 2 November is a time for remembering dead family members and friends. Many Filipinos travel back to their hometowns for family gatherings of festive remembrance.[10]

text: Trick-or treating is gradually replacing the dying tradition of Pangangaluluwâ, a local analogue of the old English custom of souling. People in the provinces still observe Pangangaluluwâ by going in groups to every house and offering a song in exchange for money or food. The participants, usually children, would sing carols about the souls in Purgatory, with the abúloy (alms for the dead) used to pay for Masses for these souls. Along with the requested alms, householders sometimes gave the children suman (rice cakes). During the night, various small items, such as clothing, plants, etc., would "mysteriously" disappear, only to be discovered the next morning in the yard or in the middle of the street. In older times, it was believed that the spirits of ancestors and loved ones visited the living on this night, manifesting their presence by taking an item.[11]

text: As the observation of Christmas traditions in the Philippines begins as early as September, it is a common sight to see Halloween decorations next to Christmas decorations in urban settings.[citation needed]

text: Singapore[edit]

text: Around mid-July Singapore Chinese celebrate "Zhong Yuan Jie / Yu Lan Jie" (Hungry Ghosts Festival), a time when it is believed that the spirits of the dead come back to visit their families.[12] In recent years, Halloween celebrations are becoming more popular, with influence from the west.[13] In 2012, there were over 19 major Halloween celebration events around Singapore.[14] SCAPE's Museum of Horrors held its fourth scare fest in 2014.[15] Universal Studios Singapore hosts "Halloween Horror Nights".[16]

text: Australia and New Zealand[edit]

text: While not traditionally a part of Australian culture, non-religious celebrations of Halloween modeled on North American festivities are growing increasingly popular in Australia,[17] in spite of seasonal differences and the transition from spring to summer. Criticism stems largely from the fact that Halloween has little relevance to Australian culture.[18][19] It is also considered, by some Australians, to be an unwanted American influence; as although Halloween does have Celtic/European origins, its increasing popularity in Australia is largely as a result of American pop-culture influence.[19][20] Supporters of the event claim that the critics fail to see that the event is not entirely American, but rather Celtic and is no different to embracing other cultural traditions such as Saint Patrick's Day.[21]

text: Due to the opposition to Halloween by some people, there is a growing movement where people are inviting trick-or-treaters to take part by putting a balloon or decoration on their letter box, to indicate that they are welcome to come knocking. In the past decade, the popularity of Halloween in Australia has grown.[22]

text: In New Zealand, as in neighbouring Australia, Halloween is not celebrated to the same extent as in North America, although in recent years the non-religious celebrations have been achieving some popularity especially among young children.[23][24]

text: Europe[edit]

text: Over the years, Halloween has become more successful in Europe and has been partially ousting some older customs like the Rübengeistern (de) (English: turnip ghosts, beet spirit), Martinisingen, and others.[25] The University of Graz undertook a research project about Halloween led by Editha Hörandner. According to her, the often heard claims of Celtic or pagan origin is used as a sort of "quality brand" (Gütesiegel) for the authenticity of the tradition.

text: Bosnia and Herzegovina[edit]

text: Halloween is a work day in Bosnia and Herzegovina, and not celebrated until recently. For the past few years, it has been popular among younger generations.[26] Since wearing masks has become highly popular among children and teenagers, e.g. in many Bosnian schools, both elementary as well as high schools (gymnasiums and vocational), students will usually wear costumes and masks on Halloween. There it is called Noć vještica (English: Night of Witches).

text: Germany[edit]

text: Halloween was not generally observed in Germany prior to the 1990s, but has been increasing in popularity. It has been associated with the influence of United States culture, and "Trick or Treating" (in German, "Süßes sonst gibt's Saures") has been occurring in various German cities, especially in areas such as the Dahlem neighborhood in Berlin, which was part of the American zone during the Cold War. Today, Halloween in Germany brings in 200 million euros a year, through multiple industries.[27] Halloween is celebrated by both children and adults. Adults celebrate at themed costume parties and clubs, while children go trick or treating. Complaints of vandalism associated with Halloween "Tricks" are increasing, particularly from many elderly Germans unfamiliar with "Trick or Treating."[28]

text: Ireland[edit]

text: On Halloween night, adults and children dress up as ghosts, ghouls, zombies, witches, and goblins, light bonfires, and enjoy spectacular fireworks displays – in particular, the city of Derry is home to the largest organized Halloween celebration on the island, in the form of a street carnival and fireworks display.[29]

text: Games are often played, such as bobbing for apples, in which apples, peanuts, and other nuts and fruit and some small coins are placed in a basin of water.[30] Everyone takes turns catching as many items possible using only their mouths. Another common game involves the hands-free eating of an apple hung on a string attached to the ceiling. Games of divination are also played at Halloween.[31] Colcannon is traditionally served on Halloween.[30]

text: 31 October is the busiest day of the year for the Emergency Services.[32] Bangers and fireworks are illegal in the Republic of Ireland; however, they are commonly smuggled in from Northern Ireland where they are legal.[33] Bonfires are frequently built around Halloween.[34] Trick-or-treating is popular amongst children on 31 October and Halloween parties and events are commonplace.

text: Italy[edit]

text: In Italy All Saints' Day is a public holiday. On 1 November, Tutti i Morti or All Souls' Day, families remember loved ones who have died. These are still the main holidays.[35] In some Italian tradition, children would awake on the morning of All Saints or All Souls to find small gifts from their deceased ancestors. In Sardinia, Concas de Mortu (Head of the deads), carved pumpkins that look like skulls, with candles inside are displayed.[36][37][38] Halloween is, however, gaining in popularity, and involves costume parties for young adults.[39] The traditions to carve pumpkins in a skull figure, lighting candles inside, or to beg for small gifts for the deads e.g. sweets or nuts, also belong to North Italy.[40] In Veneto these carved pumpkins were called lumère (lanterns) or suche dei morti (deads' pumpkins).[41]

text: Romania[edit]

text: Romanians observe the Feast of St. Andrew, patron saint of Romania, on 30 November. On St. Andrew's Eve ghosts are said to be about. A number of customs related to divination, in other places connected to Halloween, are associated with this night.[42] However, with the popularity of Dracula in western Europe, around Halloween the Romanian tourist industry promotes trips to locations connected to the historical Vlad Tepeș and the more fanciful Dracula of Bram Stoker. The most successful Halloween Party in Transylvania takes place in Sighișoara, the citadel where Vlad the Impaler was born.[43][dubious – discuss]

text: Both the Catholic and Orthodox Churches in Romania discourage Halloween celebrations, advising their parishioners to focus rather on the "Day of the Dead" on 1 November, when special religious observances are held for the souls of the deceased.[44] Opposition by religious and nationalist groups, including calls to ban costumes and decorations in schools in 2015, have been met with criticism.[45][46][47] Halloween parties are popular in bars and nightclubs.[48]

text: Russia[edit]

text: Celebration of Halloween began in the 1990s around the downfall of the Soviet regime, when costume and ghoulish parties spread throughout night clubs throughout Russia. Halloween is generally celebrated by younger generations and is not widely celebrated in civic society (e.g. theaters or libraries). In fact, Halloween is among the Western celebrations that the Russian government and politicians—which have grown increasingly anti-Western in the early 2010s—are trying to eliminate from public celebration.[49][50][51]

text: Poland[edit]

text: Since the fall of Communism in 1989, Halloween has become increasingly popular in Poland. Particularly, it is celebrated among younger people.

text: Switzerland[edit]

text: In Switzerland, Halloween, after first becoming popular in 1999 is on the wane, and is most popular with young adults who attend parties. Switzerland already has a "festival overload" and even though Swiss people like to dress up for any occasion, they do prefer a traditional element, such as in the Fasnacht tradition of chasing away winter using noise and masks.[52][53]

text: United Kingdom[edit]

text: England[edit]

text: In the past, on All Souls' Eve families would stay up late, and little "soul cakes" were eaten. At the stroke of midnight, there was solemn silence among households, which had candles burning in every room to guide the souls back to visit their earthly homes and a glass of wine on the table to refresh them. The tradition of giving soul cakes that originated in Great Britain and Ireland was known as souling, often seen as the origin of modern trick or treating in North America, and souling continued in parts of England as late as the 1930s, with children going from door to door singing songs and saying prayers for the dead in return for cakes or money.[54]

text: American-style Halloween celebrations have become increasingly popular with shops decorated with witches and pumpkins, and young people attending costume parties.[55]

text: Scotland[edit]

text: The name Halloween is first attested in the 16th century as a Scottish shortening of the fuller All-Hallows-Even, that is, the night before All Hallows Day.[56] Dumfries poet John Mayne's 1780 poem made note of pranks at Halloween; "What fearfu' pranks ensue!". Scottish poet Robert Burns was influenced by Maynes composition, and portrayed some of the customs in his poem Halloween (1785).[57] According to Burns, Halloween is "thought to be a night when witches, devils, and other mischief-making beings are all abroad on their baneful midnight errands".[58]

text: Among the earliest record of Guising at Halloween in Scotland is in 1895, where masqueraders in disguise carrying lanterns made out of scooped out turnips, visit homes to be rewarded with cakes, fruit and money.[59] If children approached the door of a house, they were given offerings of food. The children's practice of "guising", going from door to door in costumes for food or coins, is a traditional Halloween custom in Scotland.[60] These days children who knock on their neighbours doors have to sing a song or tell stories for a gift of sweets or money.[61]

text: A traditional Halloween game includes apple "dooking",[62] or "dunking" or (i.e., retrieving one from a bucket of water using only one's mouth), and attempting to eat, while blindfolded, a treacle/jam-coated scone hanging on a piece of string.

text: Traditional customs and lore include divination practices, ways of trying to predict the future. A traditional Scottish form of divining one's future spouse is to carve an apple in one long strip, then toss the peel over one's shoulder. The peel is believed to land in the shape of the first letter of the future spouse's name.[63]

text: Canada[edit]

text: Scottish emigration, primarily to Canada before 1870 and to the United States thereafter, brought the Scottish version of the holiday to each country. The earliest known reference to ritual begging on Halloween in English speaking North America occurs in 1911, when a newspaper in Kingston, Ontario reported that it was normal for the smaller children to go street "guising" on Halloween between 6 and 7 p.m., visiting shops and neighbours to be rewarded with nuts and candies for their rhymes and songs.[60] Canadians spend more on candy at Halloween than at any time apart from Christmas. Halloween is also a time for charitable contributions. Until 2006 when UNICEF moved to an online donation system, collecting small change for was very much a part of Canadian trick-or-treating.[64] Quebec offers themed tours of parts of the old city and historic cemeteries in the area.[65] In 2014 the hamlet of Arviat, Nunavut moved their Halloween festivities to the community hall, cancelling the practice of door-to-door "trick or treating", due to the risk of roaming polar bears.[66][67] In British Columbia it is a tradition to set off fireworks at Halloween.[68]

text: United States[edit]

text: In the United States, where lingering Puritan tradition restricted the observance of many holidays, Halloween did not become a holiday until the 19th century. The transatlantic migration of nearly two million Irish following the Irish Great Famine (1845–49) brought the holiday to the United States.

text: American librarian and author Ruth Edna Kelley wrote the first book length history of the holiday in the U.S; The Book of Hallowe'en (1919), and references souling in the chapter Hallowe'en in America; "All Hallowe'en customs in the United States are borrowed directly or adapted from those of other countries. The taste in Hallowe'en festivities now is to study old traditions, and hold a Scotch party, using Robert Burns's poem Halloween as a guide; or to go a-souling as the English used. In short, no custom that was once honored at Hallowe'en is out of fashion now".[69] The main event for children of modern Halloween in the United States and Canada is trick-or-treating, in which children, teenagers, (sometimes) young adults, and parents (accompanying their children) disguise themselves in costumes and go door-to-door in their neighborhoods, ringing each doorbell and yelling "Trick or treat!" to solicit a gift of candy or similar items.[70] Teenagers and adults will more frequently attend Halloween-themed costume parties typically hosted by friends or themed events at nightclubs either on Halloween itself or a weekend close to the holiday.

text: At the turn of the 20th century, Halloween had turned into a night of vandalism, with destruction of property and cruelty to animals and people.[71] Around 1912, the Boy Scouts, Boys Clubs, and other neighborhood organizations came together to encourage a safe celebration that would end the destruction that had become so common on this night.

text: The commercialization of Halloween in the United States did not start until the 20th century, beginning perhaps with Halloween postcards (featuring hundreds of designs), which were most popular between 1905 and 1915.[72] Dennison Manufacturing Company (which published its first Halloween catalog in 1909) and the Beistle Company were pioneers in commercially made Halloween decorations, particularly die-cut paper items.[73][74] German manufacturers specialised in Halloween figurines that were exported to the United States in the period between the two World Wars.

text: Halloween is now the United States' second most popular holiday (after Christmas) for decorating; the sale of candy and costumes is also extremely common during the holiday, which is marketed to children and adults alike. The National Confectioners Association (NCA) reported in 2005 that 80 percent of American adults planned to give out candy to trick-or-treaters.[75] The NCA reported in 2005 that 93 percent of children planned to go trick-or-treating.[76] According to the National Retail Federation, the most popular Halloween costume themes for adults are, in order: witch, pirate, vampire, cat, and clown.[77] Each year, popular costumes are dictated by various current events and pop culture icons. On many college campuses, Halloween is a major celebration, with the Friday and Saturday nearest 31 October hosting many costume parties. Other popular activities are watching horror movies and visiting haunted houses. Total spending on Halloween is estimated to be $8.4 billion.[78]

text: Events[edit]

text: Many theme parks stage Halloween events annually, such as Halloween Horror Nights at Universal Studios Hollywood and Universal Orlando, Mickey's Halloween Party and Mickey's Not-So-Scary Halloween Party at Disneyland Resort and Magic Kingdom respectively, and Knott's Scary Farm at Knott's Berry Farm. One of the more notable Halloween parades is the Village Halloween Parade which takes place in New York City. Each year approximately 50,000 costumed marchers parade up Sixth Avenue.[79] Salem, Massachusetts, site of the Salem witch trials, celebrates Halloween throughout the month of October with tours, plays, concerts, and other activities.[80] A number of venues in New York's lower Hudson Valley host various events to showcase a connection with Washington Irving's Legend of Sleepy Hollow. Van Cortlandt Manor stages the "Great Jack o' Lantern Blaze" featuring thousands of lighted carved pumpkins.[81]

text: Some locales have had to modify their celebrations due to disruptive behavior on the part of young adults. Madison, Wisconsin hosts an annual Halloween celebrations. In 2002 due to the large crowds in the State Street area, a riot broke out, necessitating the use of mounted police and tear gas to disperse the crowds.[82] Likewise, Chapel Hill, site of the University of North Carolina, has a downtown street party which in 2007 drew a crowd estimated at 80,000 on downtown Franklin Street, in a town with a population of just 54,000. In 2008, in an effort to curb the influx of out-of-towners, mayor Kevin Foy put measures in place to make commuting downtown more difficult on Halloween.[83] In 2014, large crowds of college students rioted at the Keene, New Hampshire Pumpkin Fest,[84] whereupon the City Council voted not to grant a permit for the following year's festival,[85] and organizers moved the event to Laconia for 2015.[86]

text: Elsewhere[edit]

text: Saint Helena[edit]

text: In Saint Helena, Halloween is actively celebrated, largely along the American model, with ghosts, skeletons, devils, vampires, witches and the like. Imitation pumpkins are used instead of real pumpkins because the pumpkin harvesting season in Saint Helena's hemisphere is not near Halloween. Trick-or-treating is widespread. Party venues provide entertainment for adults.[87]

text: Dubai[edit]

text: The "Wild Wadi Waterpark" in Dubai hosts a "Spooktacular Halloween".[88] The annual Halloween masquerade ballroom dancing party takes place at "Dance For You" studio.[89]

text: Dominican Republic[edit]

text: In the Dominican Republic it has been gaining popularity, largely due to many Dominicans living in the States and then bringing it to the island. In the larger cities of Santiago or Santo Domingo it has become more common to see children trick-or-treating, but in smaller towns and villages it is almost entirely absent, partly due to religious opposition. Tourist areas such as Sosua and Punta Cana feature many venues with Halloween celebrations, predominantly geared towards adults.[90]


document_title: History of the telescope

question_text: when was the first telescope used to observe space

text: History of the telescope

text: Optical telescopes

text: Optical foundations

text: Greek accounts of the optical properties of water filled spheres (5th century BC) followed by many centuries of writings on optics, including Ptolemy (in his work Optics written in the 2nd century AD) wrote about the properties of light including reflection, refraction, and color and Persian scholar Ibn Sahl 10th century work.[6][6]

text: Objects resembling lenses date back 4000 years although it is unknown if they were used for their optical properties or just as decoration.[7] Actual use of lenses dates back to the widespread manufacture and use of eyeglasses in the 13th century.[8][7][9] It is generally considered that spectacles for correcting long sightedness with convex lenses were invented in Northern Italy in the late 13th to early 14th century in Venice and Florence[10] and later expanded to the Netherlands and Germany.[11] The invention of the use of concave lenses to correct near-sightedness is ascribed to Nicholas of Cusa in 1451.

text: Invention

text: The first record of a telescope comes from the Netherlands in 1608. It is in a patent filed by Middelburg spectacle-maker Hans Lippershey with the States General of the Netherlands on 2 October 1608 for his instrument "for seeing things far away as if they were nearby".[12] A few weeks later another Dutch instrument-maker, Jacob Metius also applied for a patent. The States General did not award a patent since the knowledge of the device already seemed to be ubiquitous[13][14] but the Dutch government awarded Lippershey with a contract for copies of his design.

text: The original Dutch telescopes were composed of a convex and a concave lens—telescopes that are constructed this way do not invert the image. Lippershey's original design had only 3x magnification. Telescopes seem to have been made in the Netherlands in considerable numbers soon after this date of "invention", and rapidly found their way all over Europe.[citation needed]

text: Claims of prior invention

text: In 1655 Dutch diplomat William de Boreel tried to solve the mystery of who invented the telescope. He had a local magistrate in Middelburg follow up on Boreel's childhood and early adult recollections of a spectacle maker named "Hans" who he remembered as the inventor of the telescope. The magistrate was contacted by a then unknown claimant, Middelburg spectacle maker Johannes Zachariassen, who testified that his father, Zacharias Janssen invented the telescope and the microscope as early as 1590. This testimony seemed convincing to Boreel, who now recollected that Zacharias and his father, Hans Martens, must have been who he remembered.[17] Boreel's conclusion that Zacharias Janssen invented the telescope a little ahead of another spectacle maker, Hans Lippershey, was adopted by Pierre Borel in his 1656 book De vero telescopii inventore.[18][19] Discrepancies in Boreel's investigation and Zachariassen's testimony (including Zachariassen misrepresenting his date of birth and role in the invention) has led some historians to consider this claim dubious.[20] The "Janssen" claim would continue over the years and be added on to with Zacharias Snijder in 1841 presenting 4 iron tubes with lenses in them claimed to be 1590 examples of Janssen's telescope[21] and historian Cornelius De Waard's 1906 claim that the man who tried to sell a broken telescope to astronomer Simon Marius at the 1608 Frankfurt Book Fair must have been Janssen.[22]

text: In 1682,[23] the minutes of the Royal Society in London Robert Hooke noted Thomas Digges' 1571 Pantometria, (a book on measurement, partially based on his father Leonard Digges' notes and observations) seemed to give an English claim to the invention of the telescope, describing Leonard as having a fare seeing glass in the mid 1500s based on an idea by Roger Bacon:[24][25] This seemed to give an English claim to the invention of the telescope. Thomas described it as "by proportional Glasses duly situate in convenient angles, not only discovered things far off, read letters, numbered pieces of money with the very coin and superscription thereof, cast by some of his friends of purpose upon downs in open fields, but also seven miles off declared what hath been done at that instant in private places." Comments on the use of proportional or "perspective glass" are also made in the writings of John Dee (1575) and William Bourne (1585).[26] Bourne was asked in 1580 to investigate the Diggs device by Queen Elizabeth I's chief advisor Lord Burghley. Bourne's is the best description of it, and from his writing it seemed to consist of peering into a large curved mirror that reflected the image produced by a large lens.[27] The idea of an "Elizabethan Telescope" has been expanded over the years, including astronomer and historian Colin Ronan 1990s explorations concluding this reflecting/refracting telescope was built by Leonard Digges between 1540 and 1559.[28][29][30] This "backwards" reflecting telescope would have been unwieldy, it needed very large mirrors and lens to work, the observer had to stand backwards to look at an upside down view, and Bourne noted it had a very narrow field of view making it unsuitable for military purposes.[27] The optical performance required to see the details of coins lying about in fields, or private activities seven miles away, seems to be far beyond the technology of the time[31] and it could be the "perspective glass" being described was a far simpler idea, originating with Bacon, of using a single lens held in front of the eye to magnify a distant view.[32]

text: A 1959 research paper by Simon de Guilleuma claimed that evidence he had uncovered pointed to the French born spectacle maker Juan Roget (died before 1624) as another possible builder of an early telescope that predated Hans Lipperhey's patent application.[33] inventing early telescope-like devices.

text: Spread through Europe

text: Lippershey's application for a patent was mentioned at the end of a diplomatic report on an embassy to Holland from the Kingdom of Siam sent by the Siamese king Ekathotsarot: Ambassades du Roy de Siam envoyé à l'Excellence du Prince Maurice, arrivé à La Haye le 10 Septemb. 1608 (Embassy of the King of Siam sent to his Excellency Prince Maurice, arrived at The Hague on 10 September 1608). This report was issued in October 1608 and distributed across Europe, leading to experiments by other scientists, such as the Italian Paolo Sarpi, who received the report in November, and the English mathematician and astronomer Thomas Harriot, who used a six-powered telescope by the summer of 1609 to observe features on the moon.[34]

text: The Italian polymath Galileo Galilei was in Venice in June 1609[35] and there heard of the "Dutch perspective glass" by means of which distant objects appeared nearer and larger. Galileo states that he solved the problem of the construction of a telescope the first night after his return to Padua from Venice and made his first telescope the next day by fitting a convex lens in one extremity of a leaden tube and a concave lens in the other one. A few days afterwards, having succeeded in making a better telescope than the first, he took it to Venice where he communicated the details of his invention to the public and presented the instrument itself to the doge Leonardo Donato, who was sitting in full council. The senate in return settled him for life in his lectureship at Padua and doubled his salary.

text: Galileo spent his time to improving the telescope, producing telescopes of increased power. His first telescope had a 3x magnification, but he soon made instruments which magnified 8x and finally, one nearly a meter long with a 37mm objective (which he would stop down to 16mm or 12mm) and a 23x magnification.[36] With this last instrument he began a series of astronomical observations in October or November 1609, discovering the satellites of Jupiter, hills and valleys on the Moon, the phases of Venus[37] and observed spots on the sun. Galileo noted that the revolution of the satellites of Jupiter, the phases of Venus, rotation of the Sun and the tilted path its spots followed for part of the year pointed to the validity of the sun centered Copernican system over other Earth centered systems such as the one proposed by Ptolemy. Galileo's instrument was the first to be given the name "telescope". The name was invented by the Greek poet/theologian Giovanni Demisiani at a banquet held on April 14, 1611 by Prince Federico Cesi to make Galileo Galilei a member of the Accademia dei Lincei.[38] The word was created from the Greek tele = 'far' and skopein = 'to look or see'; teleskopos = 'far-seeing'.

text: These observations, together with Galileo's improvement of the instrument, led to the adoption of the name of the Galilean telescope for these early forms of telescope that employed a negative lens.[39]

text: Further refinements

text: Refracting telescopes

text: Johannes Kepler first explained the theory and some of the practical advantages of a telescope constructed of two convex lenses in his Catoptrics (1611). The first person who actually constructed a telescope of this form was the Jesuit Christoph Scheiner who gives a description of it in his Rosa Ursina (1630).[39]

text: William Gascoigne was the first who commanded a chief advantage of the form of telescope suggested by Kepler: that a small material object could be placed at the common focal plane of the objective and the eyepiece. This led to his invention of the micrometer, and his application of telescopic sights to precision astronomical instruments. It was not till about the middle of the 17th century that Kepler's telescope came into general use: not so much because of the advantages pointed out by Gascoigne, but because its field of view was much larger than in the Galilean telescope.[39]

text: The first powerful telescopes of Keplerian construction were made by Christiaan Huygens after much labor—in which his brother assisted him. With one of these: an objective diameter of 2.24 inches (57 mm) and a 12 ft (3.7 m) focal length,[40] he discovered the brightest of Saturn's satellites (Titan) in 1655; in 1659, he published his "Systema Saturnium" which, for the first time, gave a true explanation of Saturn's ring—founded on observations made with the same instrument.[39]

text: Long focal length refractors

text: The sharpness of the image in Kepler's telescope was limited by the chromatic aberration introduced by the non-uniform refractive properties of the objective lens. The only way to overcome this limitation at high magnifying powers was to create objectives with very long focal lengths. Giovanni Cassini discovered Saturn's fifth satellite (Rhea) in 1672 with a telescope 35 feet (11 m) long. Astronomers such as Johannes Hevelius were constructing telescopes with focal lengths as long as 150 feet (46 m). Besides having really long tubes these telescopes needed scaffolding or long masts and cranes to hold them up. Their value as research tools was minimal since the telescope's frame "tube" flexed and vibrated in the slightest breeze and sometimes collapsed altogether.[41][42]

text: Aerial telescopes

text: In some of the very long refracting telescopes constructed after 1675, no tube was employed at all. The objective was mounted on a swiveling ball-joint on top of a pole, tree, or any available tall structure and aimed by means of string or connecting rod. The eyepiece was handheld or mounted on a stand at the focus, and the image was found by trial and error. These were consequently termed aerial telescopes.[43] and have been attributed to Christiaan Huygens and his brother Constantijn Huygens, Jr.[41][44] although it is not clear that they invented it.[45] Christiaan Huygens and his brother made objectives up to 8.5 inches (220 mm) diameter[40] and 210 ft (64 m) focal length and others such as Adrien Auzout made telescopes with focal lengths up to 600 ft (180 m). Telescopes of such great length were naturally difficult to use and must have taxed to the utmost the skill and patience of the observers.[39] Aerial telescopes were employed by several other astronomers. Cassini discovered Saturn's third and fourth satellites in 1684 with aerial telescope objectives made by Giuseppe Campani that were 100 and 136 ft (30 and 41 m) in focal length.

text: Reflecting telescopes

text: The ability of a curved mirror to form an image may have been known since the time of Euclid[46] and had been extensively studied by Alhazen in the 11th century. Galileo, Giovanni Francesco Sagredo, and others, spurred on by their knowledge that curved mirrors had similar properties to lenses, discussed the idea of building a telescope using a mirror as the image forming objective.[47] Niccolò Zucchi, an Italian Jesuit astronomer and physicist, wrote in his book Optica philosophia of 1652 that he tried replacing the lens of a refracting telescope with a bronze concave mirror in 1616. Zucchi tried looking into the mirror with a hand held concave lens but did not get a satisfactory image, possibly due to the poor quality of the mirror, the angle it was tilted at, or the fact that his head partially obstructed the image.[48]

text: In 1636 Marin Mersenne proposed a telescope consisting of a paraboloidal primary mirror and a paraboloidal secondary mirror bouncing the image through a hole in the primary, solving the problem of viewing the image.[49] James Gregory went into further detail in his book Optica Promota (1663), pointing out that a reflecting telescope with a mirror that was shaped like the part of a conic section, would correct spherical aberration as well as the chromatic aberration seen in refractors. The design he came up with bears his name: the "Gregorian telescope"; but according to his own confession, Gregory had no practical skill and he could find no optician capable of realizing his ideas and after some fruitless attempts, was obliged to abandon all hope of bringing his telescope into practical use.

text: In 1666 Isaac Newton, based on his theories of refraction and color, perceived that the faults of the refracting telescope were due more to a lens's varying refraction of light of different colors than to a lens's imperfect shape. He concluded that light could not be refracted through a lens without causing chromatic aberrations, although he incorrectly concluded from some rough experiments[51] that all refracting substances would diverge the prismatic colors in a constant proportion to their mean refraction. From these experiments Newton concluded that no improvement could be made in the refracting telescope.[52] Newton's experiments with mirrors showed that they did not suffer from the chromatic errors of lenses, for all colors of light the angle of incidence reflected in a mirror was equal to the angle of reflection, so as a proof to his theories Newton set out to build a reflecting telescope.[53] Newton completed his first telescope in 1668 and it is the earliest known functional reflecting telescope.[54] After much experiment, he chose an alloy (speculum metal) of tin and copper as the most suitable material for his objective mirror. He later devised means for grinding and polishing them, but chose a spherical shape for his mirror instead of a parabola to simplify construction. He added to his reflector what is the hallmark of the design of a "Newtonian telescope", a secondary "diagonal" mirror near the primary mirror's focus to reflect the image at 90° angle to an eyepiece mounted on the side of the telescope. This unique addition allowed the image to be viewed with minimal obstruction of the objective mirror. He also made all the tube, mount, and fittings. Newton's first compact reflecting telescope had a mirror diameter of 1.3 inches and a focal ratio of f/5.[55] With it he found that he could see the four Galilean moons of Jupiter and the crescent phase of the planet Venus. Encouraged by this success, he made a second telescope with a magnifying power of 38x which he presented to the Royal Society of London in December 1672. This type of telescope is still called a Newtonian telescope.

text: A third form of reflecting telescope, the "Cassegrain reflector" was devised in 1672 by Laurent Cassegrain. The telescope had a small convex hyperboloidal secondary mirror placed near the prime focus to reflect light through a central hole in the main mirror.

text: No further practical advance appears to have been made in the design or construction of the reflecting telescopes for another 50 years until John Hadley (best known as the inventor of the octant) developed ways to make precision aspheric and parabolic speculum metal mirrors. In 1721 he showed the first parabolic Newtonian reflector to the Royal Society.[56] It had a 6-inch (15 cm) diameter, 62 3⁄4-inch (159 cm) focal length speculum metal objective mirror. The instrument was examined by James Pound and James Bradley.[57] After remarking that Newton's telescope had lain neglected for fifty years, they stated that Hadley had sufficiently shown that the invention did not consist in bare theory. They compared its performance with that of a 7.5 inches (190 mm) diameter aerial telescope originally presented to the Royal Society by Constantijn Huygens, Jr. and found that Hadley's reflector, "will bear such a charge as to make it magnify the object as many times as the latter with its due charge", and that it represents objects as distinct, though not altogether so clear and bright.

text: Bradley and Samuel Molyneux, having been instructed by Hadley in his methods of polishing speculum metal, succeeded in producing large reflecting telescopes of their own, one of which had a focal length of 8 ft (2.4 m). These methods of fabricating mirrors were passed on by Molyneux to two London opticians —Scarlet and Hearn— who started a business manufacturing telescopes.[58]

text: The British mathematician, optician James Short began experimenting with building telescopes based on Gregory's designs in the 1730s. He first tried making his mirrors out of glass as suggested by Gregory, but he later switched to speculum metal mirrors creating Gregorian telescopes with original designers parabolic and elliptic figures. Short then adopted telescope-making as his profession which he practised first in Edinburgh, and afterward in London. All Short's telescopes were of the Gregorian form. Short died in London in 1768, having made a considerable fortune selling telescopes.

text: Since speculum metal mirror secondaries or diagonal mirrors greatly reduced the light that reached the eyepiece, several reflecting telescope designers tried to do away with them. In 1762 Mikhail Lomonosov presented a reflecting telescope before the Russian Academy of Sciences forum. It had its primary mirror tilted at four degrees to telescope's axis so the image could be viewed via an eyepiece mounted at the front of the telescope tube without the observer's head blocking the incoming light. This innovation was not published until 1827, so this type came to be called the Herschelian telescope after a similar design by William Herschel.[59]

text: About the year 1774 William Herschel (then a teacher of music in Bath, England) began to occupy his leisure hours with the construction of reflector telescope mirrors, finally devoted himself entirely to their construction and use in astronomical research. In 1778, he selected a 6 1⁄4-inch (16 cm) reflector mirror (the best of some 400 telescope mirrors which he had made) and with it, built a 7-foot (2.1 m) focal length telescope. Using this telescope, he made his early brilliant astronomical discoveries. In 1783, Herschel completed a reflector of approximately 18 inches (46 cm) in diameter and 20 ft (6.1 m) focal length. He observed the heavens with this telescope for some twenty years, replacing the mirror several times. In 1789 Herschel finished building his largest reflecting telescope with a mirror of 49 inches (120 cm) and a focal length of 40 ft (12 m), (commonly known as his 40-foot telescope) at his new home, at Observatory House in Slough, England. To cut down on the light loss from the poor reflectivity of the speculum mirrors of that day, Herschel eliminated the small diagonal mirror from his design and tilted his primary mirror so he could view the formed image directly. This design has come to be called the Herschelian telescope. He discovered Saturn's sixth known moon, Enceladus, the first night he used it (August 28, 1789), and on September 17, its seventh known moon, Mimas. This telescope was world's largest telescope for over 50 years. However, this large scope was difficult to handle and thus less used than his favorite 18.7-inch reflector.

text: In 1845 William Parsons, 3rd Earl of Rosse built his 72-inch (180 cm) Newtonian reflector called the "Leviathan of Parsonstown" with which he discovered the spiral form of galaxies.

text: All of these larger reflectors suffered from the poor reflectivity and fast tarnishing nature of their speculum metal mirrors. This meant they need more than one mirror per telescope since mirrors had to be frequently removed and re-polished. This was time consuming since the polishing process could change the curve of the mirror so it usually had to be "re-figured" to the correct shape.

text: Achromatic refracting telescopes

text: From the time of the invention of the first refracting telescopes it was generally supposed that chromatic errors seen in lenses simply arose from errors in the spherical figure of their surfaces. Opticians tried to construct lenses of varying forms of curvature to correct these errors.[39] Isaac Newton discovered in 1666 that chromatic colors actually arose from the un-even refraction of light as it passed through the glass medium. This led opticians to experiment with lenses constructed of more than one type of glass in an attempt to canceling the errors produced by each type of glass. It was hoped that this would create an "achromatic lens"; a lens that would focus all colors to a single point, and produce instruments of much shorter focal length.

text: The first person who succeeded in making a practical achromatic refracting telescope was Chester Moore Hall from Essex, England.[citation needed] He argued that the different humours of the human eye refract rays of light to produce an image on the retina which is free from color, and he reasonably argued that it might be possible to produce a like result by combining lenses composed of different refracting media. After devoting some time to the inquiry he found that by combining two lenses formed of different kinds of glass, he could make an achromatic lens where the effects of the unequal refractions of two colors of light (red and blue) was corrected. In 1733, he succeeded in constructing telescope lenses which exhibited much reduced chromatic aberration. One of his instruments had an objective measuring 2 1⁄2 inches (6.4 cm) with a relatively short focal length of 20 inches (51 cm).

text: Hall was a man of independent means and seems to have been careless of fame; at least he took no trouble to communicate his invention to the world. At a trial in Westminster Hall about the patent rights granted to John Dollond (Watkin v. Dollond), Hall was admitted to be the first inventor of the achromatic telescope. However, it was ruled by Lord Mansfield that it was not the original inventor who ought to profit from such invention, but the one who brought it forth for the benefit of mankind.

text: In 1747, Leonhard Euler sent to the Prussian Academy of Sciences a paper in which he tried to prove the possibility of correcting both the chromatic and the spherical aberration of a lens. Like Gregory and Hall, he argued that since the various humours of the human eye were so combined as to produce a perfect image, it should be possible by suitable combinations of lenses of different refracting media to construct a perfect telescope objective. Adopting a hypothetical law of the dispersion of differently colored rays of light, he proved analytically the possibility of constructing an achromatic objective composed of lenses of glass and water.

text: All of Euler's efforts to produce an actual objective of this construction were fruitless—a failure which he attributed solely to the difficulty of procuring lenses that worked precisely to the requisite curves.[60] John Dollond agreed with the accuracy of Euler's analysis, but disputed his hypothesis on the grounds that it was purely a theoretical assumption: that the theory was opposed to the results of Newton's experiments on the refraction of light, and that it was impossible to determine a physical law from analytical reasoning alone.[61]

text: In 1754, Euler sent to the Berlin Academy a further paper in which starting from the hypothesis that light consists of vibrations excited in an elastic fluid by luminous bodies—and that the difference of color of light is due to the greater or lesser frequency of these vibrations in a given time— he deduced his previous results. He did not doubt the accuracy of Newton's experiments quoted by Dollond.

text: Dollond did not reply to this, but soon afterwards he received an abstract of a paper by the Swedish mathematician and astronomer, Samuel Klingenstierna, which led him to doubt the accuracy of the results deduced by Newton on the dispersion of refracted light. Klingenstierna showed from purely geometrical considerations (fully appreciated by Dollond) that the results of Newton's experiments could not be brought into harmony with other universally accepted facts of refraction.

text: As a practical man, Dollond at once put his doubts to the test of experiment: he confirmed the conclusions of Klingenstierna, discovered a difference far beyond his hopes in the refractive qualities of different kinds of glass with respect to the divergence of colors, and was thus rapidly led to the construction of lenses in which first the chromatic aberration—and afterwards—the spherical aberration were corrected.[62]

text: Dollond was aware of the conditions necessary for the attainment of achromatism in refracting telescopes, but relied on the accuracy of experiments made by Newton. His writings show that with the exception of his bravado, he would have arrived sooner at a discovery for which his mind was fully prepared. Dollond's paper[62] recounts the successive steps by which he arrived at his discovery independently of Hall's earlier invention—and the logical processes by which these steps were suggested to his mind.

text: In 1765 Peter Dollond (son of John Dollond) introduced the triple objective, which consisted of a combination of two convex lenses of crown glass with a concave flint lens between them. He made many telescopes of this kind.[citation needed]

text: The difficulty of procuring disks of glass (especially of flint glass) of suitable purity and homogeneity limited the diameter and light gathering power of the lenses found in the achromatic telescope. It was in vain that the French Academy of Sciences offered prizes for large perfect disks of optical flint glass.

text: The difficulties with the impractical metal mirrors of reflecting telescopes led to the construction of large refracting telescopes. By 1866 refracting telescopes had reached 18 inches (46 cm) in aperture with many larger "Great refractors" being built in the mid to late 19th century. In 1897, the refractor reached its maximum practical limit in a research telescope with the construction of the Yerkes Observatorys' 40-inch (100 cm) refractor (although a larger refractor Great Paris Exhibition Telescope of 1900 with an objective of 49.2 inches (1.25 m) diameter was temporarily exhibited at the Paris 1900 Exposition). No larger refractors could be built because of gravity's effect on the lens. Since a lens can only be held in place by its edge, the center of a large lens will sag due to gravity, distorting the image it produces.[63]

text: Large reflecting telescopes

text: In 1856–57, Karl August von Steinheil and Léon Foucault introduced a process of depositing a layer of silver on glass telescope mirrors. The silver layer was not only much more reflective and longer lasting than the finish on speculum mirrors, it had the advantage of being able to be removed and re-deposited without changing the shape of the glass substrate. Towards the end of the 19th century very large silver on glass mirror reflecting telescopes were built.

text: The beginning of the 20th century saw construction of the first of the "modern" large research reflectors, designed for precision photographic imaging and located at remote high altitude clear sky locations[64] such as the 60-inch Hale telescope of 1908, and the 100-inch (2.5 m) Hooker telescope in 1917, both located at Mount Wilson Observatory.[65] These and other telescopes of this size had to have provisions to allow for the removal of their main mirrors for re-silvering every few months. John Donavan Strong, a young physicist at the California Institute of Technology, developed a technique for coating a mirror with a much longer lasting aluminum coating using thermal vacuum evaporation. In 1932, he became the first person to "aluminize" a mirror; three years later the 60-inch (1,500 mm) and 100-inch (2,500 mm) telescopes became the first large astronomical telescopes to have their mirrors aluminized.[66] 1948 saw the completion of the 200-inch (510 cm) Hale reflector at Mount Palomar which was the largest telescope in the world up until the completion of the massive 605 cm (238 in) BTA-6 in Russia twenty-seven years later. The Hale reflector introduced several technical innovations used in future telescopes, including hydrostatic bearings for very low friction, the Serrurier truss for equal deflections of the two mirrors as the tube sags under gravity, and the use of Pyrex low-expansion glass for the mirrors. The arrival of substantially larger telescopes had to await the introduction of methods other than the rigidity of glass to maintain the proper shape of the mirror.

text: Active and adaptive optics

text: The 1980s saw the introduction of two new technologies for building larger telescopes and improving image quality, known as active optics and adaptive optics. In active optics, an image analyser senses the aberrations of a star image a few times per minute, and a computer adjusts many support forces on the primary mirror and the location of the secondary mirror to maintain the optics in optimal shape and alignment. This is too slow to correct for atmospheric blurring effects, but enables the use of thin single mirrors up to 8 m diameter, or even larger segmented mirrors. This method was pioneered by the ESO New Technology Telescope in the late 1980s.

text: The 1990s saw a new generation of giant telescopes appear using active optics, beginning with the construction of the first of the two 10 m (390 in) Keck telescopes in 1993. Other giant telescopes built since then include: the two Gemini telescopes, the four separate telescopes of the Very Large Telescope, and the Large Binocular Telescope.

text: Adaptive optics uses a similar principle, but applying corrections several hundred times per second to compensate the effects of rapidly changing optical distortion due to the motion of turbulence in the Earth's atmosphere. Adaptive optics works by measuring the distortions in a wavefront and then compensating for them by rapid changes of actuators applied to a small deformable mirror or with a liquid crystal array filter. AO was first envisioned by Horace W. Babcock in 1953, but did not come into common usage in astronomical telescopes until advances in computer and detector technology during the 1990s made it possible to calculate the compensation needed in real time.[67] In adaptive optics, the high-speed corrections needed mean that a fairly bright star is needed very close to the target of interest (or an artificial star is created by a laser). Also, with a single star or laser the corrections are only effective over a very narrow field (tens of arcsec), and current systems operating on several 8-10m telescopes work mainly in near-infrared wavelengths for single-object observations.

text: Developments of adaptive optics include systems with multiple lasers over a wider corrected field, and/or working above kiloHertz rates for good correction at visible wavelengths; these are currently in progress but not yet in routine operation as of 2015.

text: Other wavelengths

text: The twentieth century saw the construction of telescopes which could produce images using wavelengths other than visible light starting in 1931 when Karl Jansky discovered astronomical objects gave off radio emissions; this prompted a new era of observational astronomy after World War II, with telescopes being developed for other parts of the electromagnetic spectrum from radio to gamma-rays.

text: Radio telescopes

text: Radio astronomy began in 1931 when Karl Jansky discovered that the Milky Way was a source of radio emission while doing research on terrestrial static with a direction antenna. Building on Jansky's work, Grote Reber built a more sophisticated purpose-built radio telescope in 1937, with a 31.4-foot (9.6 m) dish; using this, he discovered various unexplained radio sources in the sky. Interest in radio astronomy grew after the Second World War when much larger dishes were built including: the 250-foot (76 m) Jodrell bank telescope (1957), the 300-foot (91 m) Green Bank Telescope (1962), and the 100-metre (330 ft) Effelsberg telescope (1971). The huge 1,000-foot (300 m) Arecibo telescope (1963) is so large that it is fixed into a natural depression in the ground; the central antenna can be steered to allow the telescope to study objects up to twenty degrees from the zenith. However, not every radio telescope is of the dish type. For example, the Mills Cross Telescope (1954) was an early example of an array which used two perpendicular lines of antennae 1,500 feet (460 m) in length to survey the sky.

text: High-energy radio waves are known as microwaves and this has been an important area of astronomy ever since the discovery of the cosmic microwave background radiation in 1964. Many ground-based radio telescopes can study microwaves. Short wavelength microwaves are best studied from space because water vapor (even at high altitudes) strongly weakens the signal. The Cosmic Background Explorer (1989) revolutionized the study of the microwave background radiation.

text: Because radio telescopes have low resolution, they were the first instruments to use interferometry allowing two or more widely separated instruments to simultaneously observe the same source. Very long baseline interferometry extended the technique over thousands of kilometers and allowed resolutions down to a few milli-arcseconds.

text: A telescope like the Large Millimeter Telescope (active since 2006) observes from 0.85 to 4 mm (850 to 4,000 µm), bridging between the far-infrared/submillimeter telescopes and longer wavelength radio telescopes including the microwave band from about 1 mm (1,000 µm) to 1,000 mm (1.0 m) in wavelength.

text: Infrared telescopes (700 nm/ 0.7 µm – 1000 µm/1 mm)

text: Although most infrared radiation is absorbed by the atmosphere, infrared astronomy at certain wavelengths can be conducted on high mountains where there is little absorption by atmospheric water vapor. Ever since suitable detectors became available, most optical telescopes at high-altitudes have been able to image at infrared wavelengths. Some telescopes such as the 3.8-metre (150 in) UKIRT, and the 3-metre (120 in) IRTF — both on Mauna Kea — are dedicated infrared telescopes. The launch of the IRAS satellite in 1983 revolutionized infrared astronomy from space. This reflecting telescope which had a 60-centimetre (24 in) mirror, operated for nine months until its supply of coolant (liquid helium) ran out. It surveyed the entire sky detecting 245,000 infrared sources—more than 100 times the number previously known.

text: Ultra-violet telescopes (10 nm – 400 nm)

text: Although optical telescopes can image the near ultraviolet, the ozone layer in the stratosphere absorbs ultraviolet radiation shorter than 300 nm so most ultra-violet astronomy is conducted with satellites. Ultraviolet telescopes resemble optical telescopes, but conventional aluminium-coated mirrors cannot be used and alternative coatings such as magnesium fluoride or lithium fluoride are used instead. The Orbiting Solar Observatory satellite carried out observations in the ultra-violet as early as 1962. The International Ultraviolet Explorer (1978) systematically surveyed the sky for eighteen years, using a 45-centimetre (18 in) aperture telescope with two spectroscopes. Extreme-ultraviolet astronomy (10–100 nm) is a discipline in its own right and involves many of the techniques of X-ray astronomy; the Extreme Ultraviolet Explorer (1992) was a satellite operating at these wavelengths.

text: X-ray telescopes (0.01 nm – 10 nm)

text: X-rays from space do not reach the Earth's surface so X-ray astronomy has to be conducted above the Earth's atmosphere. The first X-ray experiments were conducted on sub-orbital rocket flights which enabled the first detection of X-rays from the Sun (1948) and the first galactic X-ray sources: Scorpius X-1 (June 1962) and the Crab Nebula (October 1962). Since then, X-ray telescopes (Wolter telescopes) have been built using nested grazing-incidence mirrors which deflect X-rays to a detector. Some of the OAO satellites conducted X-ray astronomy in the late 1960s, but the first dedicated X-ray satellite was the Uhuru (1970) which discovered 300 sources. More recent X-ray satellites include: the EXOSAT (1983), ROSAT (1990), Chandra (1999), and Newton (1999).

text: Gamma-ray telescopes (less than 0.01 nm)

text: Gamma rays are absorbed high in the Earth's atmosphere so most gamma-ray astronomy is conducted with satellites. Gamma-ray telescopes use scintillation counters, spark chambers and more recently, solid-state detectors. The angular resolution of these devices is typically very poor. There were balloon-borne experiments in the early 1960s, but gamma-ray astronomy really began with the launch of the OSO 3 satellite in 1967; the first dedicated gamma-ray satellites were SAS B (1972) and Cos B (1975). The Compton Gamma Ray Observatory (1991) was a big improvement on previous surveys. Very high-energy gamma-rays (above 200 GeV) can be detected from the ground via the Cerenkov radiation produced by the passage of the gamma-rays in the Earth's atmosphere. Several Cerenkov imaging telescopes have been built around the world including: the HEGRA (1987), STACEE (2001), HESS (2003), and MAGIC (2004).

text: Interferometric telescopes

text: In 1868, Fizeau noted that the purpose of the arrangement of mirrors or glass lenses in a conventional telescope was simply to provide an approximation to a Fourier transform of the optical wave field entering the telescope. As this mathematical transformation was well understood and could be performed mathematically on paper, he noted that by using an array of small instruments it would be possible to measure the diameter of a star with the same precision as a single telescope which was as large as the whole array— a technique which later became known as astronomical interferometry. It was not until 1891 that Albert A. Michelson successfully used this technique for the measurement of astronomical angular diameters: the diameters of Jupiter's satellites (Michelson 1891). Thirty years later, a direct interferometric measurement of a stellar diameter was finally realized by Michelson & Francis G. Pease (1921) which was applied by their 20 ft (6.1 m) interferometer mounted on the 100 inch Hooker Telescope on Mount Wilson.

text: The next major development came in 1946 when Ryle and Vonberg (Ryle and Vonberg 1946) located a number of new cosmic radio sources by constructing a radio analogue of the Michelson interferometer. The signals from two radio antennas were added electronically to produce interference. Ryle and Vonberg's telescope used the rotation of the Earth to scan the sky in one dimension. With the development of larger arrays and of computers which could rapidly perform the necessary Fourier transforms, the first aperture synthesis imaging instruments were soon developed which could obtain high resolution images without the need of a giant parabolic reflector to perform the Fourier transform. This technique is now used in most radio astronomy observations. Radio astronomers soon developed the mathematical methods to perform aperture synthesis Fourier imaging using much larger arrays of telescopes —often spread across more than one continent. In the 1980s, the aperture synthesis technique was extended to visible light as well as infrared astronomy, providing the first very high resolution optical and infrared images of nearby stars.

text: In 1995 this imaging technique was demonstrated on an array of separate optical telescopes for the first time, allowing a further improvement in resolution, and also allowing even higher resolution imaging of stellar surfaces. The same techniques have now been applied at a number of other astronomical telescope arrays including: the Navy Prototype Optical Interferometer, the CHARA array, and the IOTA array. A detailed description of the development of astronomical optical interferometry can be found here [3].

text: In 2008, Max Tegmark and Matias Zaldarriaga proposed a "Fast Fourier Transform Telescope" design in which the lenses and mirrors could be dispensed with altogether when computers become fast enough to perform all the necessary transforms.