document_title: El Clásico

question_text: who has the most trophies barcelona or real madrid

text: El Clásico

text: Rivalry

text: History

text: The conflict between Real Madrid and Barcelona has long surpassed the sporting dimension,[13][14] so that elections to the clubs' presidencies are strongly politicized.[15]

text: As early as the 1930s, Barcelona "had developed a reputation as a symbol of Catalan identity, opposed to the centralising tendencies of Madrid".[16][17] In 1936, when Francisco Franco started the Coup d'état against the democratic Second Spanish Republic, the president of Barcelona, Josep Sunyol, member of the Republican Left of Catalonia and Deputy to The Cortes, was arrested and executed without trial by Franco's troops[15] (Sunyol was exercising his political activities, visiting Republican troops north of Madrid).[16]

text: Barcelona was on top of the list of organizations to be purged by the National faction, just after communists, anarchists, and independentists.[15][18] During the Franco dictatorship, most citizens of Barcelona were in strong opposition to the fascist-like régime. Phil Ball, the author of Morbo: The Story of Spanish Football, says about the match; "they hate each other with an intensity that can truly shock the outsider".[19]

text: During the dictatorships of Miguel Primo de Rivera and of Francisco Franco, all regional languages and identities in Spain were frowned upon and restrained. In this period, Barcelona gained their motto Més que un club (English: More than a club) because of its alleged connection to Catalan nationalist as well as to progressive beliefs.[20] During Franco's regime, however, Barcelona was granted profit due to its good relationship with the dictator at management level, even giving two awards to him.[21] The links between senior Real Madrid representatives and the Francoist regime were undeniable;[15] for most of the Catalans, Real Madrid was regarded as "the establishment club", despite the fact that presidents of both clubs like Josep Sunyol and Rafael Sánchez Guerra, suffered at the hands of Franco's supporters in the Spanish Civil War.[16][22][23]

text: The image for both clubs was further affected by the creation of Ultras groups, some of which became hooligans. In 1980, Ultras Sur was founded as a far-right-leaning Real Madrid ultras group, followed in 1981 by the foundation of the initially left-leaning and later on far-right, Barcelona ultras group Boixos Nois. Both groups became known for their violent acts,[15][24][25] and one of the most conflictive factions of Barcelona supporters, the Casuals, became a full-fledged criminal organisation.[26]

text: For many people, Barcelona is still considered as "the rebellious club", or the alternative pole to "Real Madrid's conservatism".[27][28] According to polls released by CIS (Centro de Investigaciones Sociológicas), Real Madrid is the favorite team of most of the Spanish residents, while Barcelona stands in the second position. In Catalonia, forces of all the political spectrum are overwhelmingly in favour of Barcelona. Nevertheless, the support of the blaugrana club goes far beyond from that region, earning its best results among young people, sustainers of a federal structure of Spain and citizens with left-wing ideology, in contrast with Real Madrid fans which politically tend to adopt right-wing views.[29][30]

text: 1943 Copa del Generalísimo semi-finals

text: On 13 June 1943, Real Madrid beat Barcelona 11–1 at home in the second leg of a semi-final of the Copa del Generalísimo, the Copa del Rey having been renamed in honour of General Franco.[31] The first leg, played at Barcelona's Les Corts stadium in Catalonia, had ended with Barcelona winning 3–0. Madrid complained about all the three goals that referee Fombona Fernández had allowed for Barcelona,[32] with the home supporters also whistling Madrid throughout, whom they accused of employing roughhouse tactics, and Fombona for allowing them to. A campaign began in Madrid. Barcelona player Josep Valle recalled: "The press officer at the DND and ABC newspaper wrote all sorts of scurrilous lies, really terrible things, winding up the Madrid fans like never before". While former Real Madrid goalkeeper Eduardo Teus, who admitted that Madrid had "above all played hard", wrote in a newspaper: "the ground itself made Madrid concede two of the three goals, goals that were totally unfair".[33]

text: Barcelona fans were banned from traveling to Madrid. Real Madrid released a statement after the match which former club president (1985–1995) Ramón Mendoza explained, "The message got through that those fans who wanted to could go to El Club bar on Calle de la Victoria where Madrid's social center was. There, they were given a whistle. Others had whistles handed to them with their tickets." The day of the second leg, the Barcelona team were insulted and stones were thrown at their bus as soon as they left their hotel. Barcelona's striker Mariano Gonzalvo said of the incident, "Five minutes before the game had started, our penalty area was already full of coins." Barcelona goalkeeper Lluis Miró rarely approached his line—when he did, he was armed with stones. As Francisco Calvet told the story, "They were shouting: Reds! Separatists!... a bottle just missed Sospedra that would have killed him if it had hit him. It was all set up."[34]

text: Real Madrid went 2–0 up within half an hour. The third goal brought with it a sending off for Barcelona's Benito García after he made what Calvet claimed was a "completely normal tackle". Madrid's José Llopis Corona recalled, "At which point, they got a bit demoralized," while Mur countered, "at which point, we thought: 'go on then, score as many as you want'." Madrid scored in minutes 31', 33', 35', 39', 43' and 44', as well as two goals ruled out for offside, made it 8–0. Basilo de la Morena had been caught out by the speed of the goals. In that atmosphere and with a referee who wanted to avoid any complications, it was humanly impossible to play... If the azulgranas had played badly, really badly, the scoreboard would still not have reached that astronomical figure. The point is that they did not play at all." Both clubs were fined 2,500 pesetas by the Royal Spanish Football Federation and, although Barcelona appealed, it made no difference. Piñeyro resigned in protest, complaining of "a campaign that the press has run against Barcelona for a week and which culminated in the shameful day at Chamartín".[35][36]

text: The match report in the newspaper La Prensa described Barcelona's only goal as a "reminder that there was a team there who knew how to play football and that if they did not do so that afternoon, it was not exactly their fault".[37] Another newspaper called the scoreline "as absurd as it was abnormal".[32] According to football writer Sid Lowe, "There have been relatively few mentions of the game [since] and it is not a result that has been particularly celebrated in Madrid. Indeed, the 11–1 occupies a far more prominent place in Barcelona's history. This was the game that first formed the identification of Madrid as the team of the dictatorship and Barcelona as its victims."[32] Fernando Argila, Barcelona's reserve goalkeeper from the game, said, "There was no rivalry. Not, at least, until that game."[38]

text: Di Stéfano transfer

text: The rivalry was intensified during the 1950s when the clubs disputed the signing of Alfredo Di Stéfano. Di Stéfano had impressed both Barcelona and Real Madrid while playing for Los Millionarios in Bogotá, Colombia, during a players' strike in his native Argentina.[39] Both Real Madrid and Barcelona attempted to sign him and, due to confusion that emerged from Di Stéfano moving to Millonarios from River Plate following the strike, both clubs claimed to own his registration.[39] After intervention from FIFA representative Muñoz Calero, it was decided that both Barcelona and Real Madrid had to share the player in alternate seasons. Barcelona's humiliated president was forced to resign by the Barcelona board, with the interim board cancelling Di Stéfano's contract.[39] This ended the long struggle for Di Stéfano, as he moved definitively to Real Madrid.[39]

text: Di Stéfano became integral in the subsequent success achieved by Real Madrid, scoring twice in his first game against Barcelona. With him, Real Madrid won the initial five European Champions Cup competitions. The 1960s saw the rivalry reach the European stage when they met twice at the European Cup, Real Madrid winning in 1960 and Barcelona winning in 1961.

text: Luís Figo Transfer

text: In 2000, Real Madrid's then-presidential candidate, Florentino Pérez, offered Barcelona's vice-captain Luís Figo $2.4 million just to sign an agreement binding him to Madrid if he won the elections. If the player broke the deal, he would have to pay Pérez $30 million in compensation. When his agent confirmed the deal, Figo denied everything, insisting, "I'll stay at Barcelona whether Pérez wins or loses." He accused the presidential candidate of "lying" and "fantasizing". He told Barcelona teammates Luis Enrique and Pep Guardiola he was not leaving and they conveyed the message to the Barcelona squad.[40]

text: On 9 July, Sport ran an interview in which he said, "I want to send a message of calm to Barcelona's fans, for whom I always have and always will feel great affection. I want to assure them that Luís Figo will, with absolute certainty, be at the Camp Nou on the 24th to start the new season... I’ve not signed a pre-contract with a presidential candidate at Real Madrid. No. I'm not so mad as to do a thing like that."[40]

text: The only way Barcelona could prevent Figo's transfer to Real Madrid was to pay the penalty clause, $30 million. That would have effectively meant paying the fifth highest transfer fee in history to sign their own player. Barcelona's new president, Joan Gaspart, called the media and told them, "Today, Figo gave me the impression that he wanted to do two things: get richer and stay at Barça." Only one of them happened. The following day, 24 July, Figo was presented in Madrid and handed his new shirt by Alfredo Di Stéfano. His buyout clause was set at $180 million. Gaspart later admitted, "Figo's move destroyed us."[41]

text: On his return to Barcelona in a Real Madrid shirt, banners with "Judas", "Scum" and "Mercenary" were hung around the stadium. Thousands of fake 10,000 peseta notes had been printed and emblazoned with his image, were among the missiles of oranges, bottles, cigarette lighters, even a couple of mobile phones were thrown at him.[42] In his third season with Real Madrid, the 2002 Clásico at Camp Nou produced one of the defining images of the rivalry. Figo was mercilessly taunted throughout; missiles of coins, a knife, a whisky bottle, were raining down from the stands, mostly from areas populated by the Boixos Nois where he had been taking a corner. Among the debris was a pig's head.[43][44]

text: Recent issues

text: During the last three decades, the rivalry has been augmented by the modern Spanish tradition of the Pasillo, where one team is given the guard of honor by the other team, once the former clinches the La Liga trophy before El Clásico takes place. This has happened in three occasions. First, during El Clásico that took place on 30 April 1988, where Real Madrid won the championship on the previous round. Then, three years later, when Barcelona won the championship two rounds before El Clásico on 8 June 1991.[45] The last pasillo, and most recent, took place on 7 May 2008, and this time Real Madrid had won the championship.[46]

text: The two teams met again in the UEFA Champions League semi-final in 2002, with Real Madrid winning 2–0 in Barcelona and a 1–1 draw in Madrid. The match was dubbed by Spanish media as the "Match of the Century".[47]

text: While El Clásico is regarded as one of the fiercest rivalries in world football, there have been rare moments when fans have shown praise for a player on the opposing team. In 1980, Laurie Cunningham was the first Real Madrid player to receive applause from Barcelona fans at Camp Nou; after excelling during the match, and with Madrid winning 2–0, Cunningham left the field to a standing ovation from the locals.[48][49] On 26 June 1983, during the second leg of the Copa de la Liga final at the Santiago Bernabéu in Madrid, having dribbled past the Real Madrid goalkeeper, Barcelona star Diego Maradona ran towards an empty goal before stopping just as the Madrid defender came sliding in an attempt to block the shot and crashed into the post, before Maradona slotted the ball into the net.[48] The manner of Maradona's goal led to many Madrid fans inside the stadium start applauding.[48][50] In November 2005, Ronaldinho became the second Barcelona player to receive a standing ovation from Madrid fans at the Santiago Bernabéu.[48] After dribbling through the Madrid defence twice to score two goals in a 3–0 win, Madrid fans paid homage to his performance with applause.[51][52] On 21 November 2015, Andrés Iniesta became the third Barcelona player to receive applause from Real Madrid fans while he was substituted during a 4–0 away win, with Iniesta scoring Barça's third.[53]

text: A 2007 survey by the Centro de Investigaciones Sociológicas showed that 32% of the Spanish population supported Real Madrid, while 25% supported Barcelona. In third place came Valencia, with 5%.[54] According to a poll performed by Ikerfel in 2011, Barcelona is the most popular team in Spain with 44% of preferences, while Real Madrid is second with 37%. Atlético Madrid, Valencia and Athletic Bilbao complete the top five.[55] Both clubs have a global fanbase and are the world's two most followed sports teams on social media—on Facebook, as of March 2016, Barcelona has 91 million fans, Real Madrid has 87 million fans.[11][56]

text: The rivalry intensified in 2011 where, due to the final of the Copa Del Rey and the meeting of the two in the UEFA Champions League, Barcelona and Real Madrid were scheduled to meet each other four times in 18 days. Several accusations of unsportsmanlike behaviour from both teams and a war of words erupted throughout the fixtures which included four red cards. Spain national team coach Vicente del Bosque stated that he was "concerned" that due to the rising hatred between the two clubs, that this could cause friction in the Spain team.[57]

text: In recent years, the rivalry has been "encapsulated" by the rivalry between Cristiano Ronaldo and Lionel Messi.[58] Following the star signings of Neymar and Luis Suárez to Barcelona, and Gareth Bale and Karim Benzema to Madrid, the rivalry has been expanded to a battle of the clubs attacking trios, "BBC" (Bale, Benzema, Cristiano) against "MSN" (Messi, Suárez, Neymar).[59]

text: Results

text:
Matches
Wins
Draws
Goals
Home Wins
Home Draws
Away Wins

M
B
M
B
M
B
M
B
M
B

La Liga
176
72
70
34
286
282
52
49
15
19
20
21

Copa del Rey
33
12
14
7
64
63
5
7
5
2
3
5

Copa de la Liga
6
0
2
4
8
13
0
1
2
2
0
1

Supercopa de España
14
8
4
2
30
18
6
4
1
1
2
0

Champions League
8
3
2
3
13
10
1
1
2
1
2
1

All competitions
237
95
92
50
401
386
64
61
25
25
27
28

Friendly
34
4
20
10
44
86
3
11
4
6
1
8

All matches
271
99
112
60
445
472
67
72
29
31
28
36

text: Records

text: Biggest wins (5+ goals)

text:
10
Real Madrid 11–1 Barcelona
19 June 1943
Copa del Rey

6
Real Madrid 8–2 Barcelona
3 February 1935
La Liga

5
Barcelona 7–2 Real Madrid
24 September 1950
La Liga

Barcelona 6–1 Real Madrid
19 May 1957
Copa del Rey

Real Madrid 6–1 Barcelona
18 September 1949
La Liga

Barcelona 5–0 Real Madrid
21 April 1935

Barcelona 5–0 Real Madrid
25 March 1945

Real Madrid 5–0 Barcelona
5 October 1953

Real Madrid 0–5 Barcelona
17 February 1974

Barcelona 5–0 Real Madrid
8 January 1994

Real Madrid 5–0 Barcelona
7 January 1995

Barcelona 5–0 Real Madrid
29 November 2010

text: Longest runs

text: Most consecutive wins

text:
Games
Club
Period

6
Barcelona
25 January 1948 – 15 January 1949

6
Real Madrid
30 September 1962 – 28 February 1965

5
Real Madrid
5 March 1933 – 3 February 1935

5
Barcelona
13 December 2008 – 29 November 2010

text: Most consecutive draws

text:
Games
Period

3
11 September 1991 – 7 March 1992

3
1 May 2002 – 20 April 2003

text: Most consecutive matches without a draw

text:
Games
Period

18
25 January 1948 – 21 November 1954

17
23 November 1960 – 19 March 1967

14
4 December 1977 – 4 June 1983

12
19 May 1957 – 27 April 1960

10
5 March 1933 – 28 January 1940

text: Longest undefeated runs

text:
Games
Club
Period

14
Real Madrid
31 January 1931 – 3 February 1935

13
Barcelona
1 November 1917 – 3 June 1928

text: Longest undefeated runs in the league

text:
Games
Club
Period

7 (5 Wins)
Real Madrid
31 January 1932 – 3 February 1935

7 (5 Wins)
Barcelona
13 December 2008 – 10 December 2011

6 (6 Wins)
Real Madrid
30 September 1962 – 28 February 1965

6 (4 Wins)
Barcelona
11 May 1997 – 13 October 1999

6 (3 Wins)
Barcelona
28 November 1971 – 17 February 1974

5 (4 Wins)
Barcelona
30 March 1947 – 15 January 1949

5 (3 Wins)
Barcelona
11 May 1975 – 30 January 1977

text: Most consecutive matches without conceding a goal

text:
Games
Club
Period

5
Barcelona
3 April 1972 – 17 February 1974

3
Barcelona
10 January 1914 – 7 March 1916

3
Real Madrid
29 June 1974 – 11 May 1975

3
Barcelona
29 November 2009 – 29 November 2010

text: Most consecutive games scoring

text:
Games
Club
Period

23
Barcelona
27 April 2011 – 13 August 2017

18
Real Madrid
3 May 2011 – 22 March 2015

17
Barcelona
27 November 1982 – 31 January 1987

14
Real Madrid
15 February 1959 – 21 January 1962

14
Real Madrid
5 December 1990 – 16 December 1993

13
Real Madrid
1 December 1946 – 23 November 1952

13
Real Madrid
22 April 1962 – 9 April 1968

12
Barcelona
26 March 1916 – 26 April 1926

11
Barcelona
11 September 1991 – 7 May 1994

10
Barcelona
30 January 1997 – 13 October 1999

text: Goalscoring

text: Top goalscorers

text: Players in bold are still active

text:
Player
Club
La Liga
Copa
Super Cup
League Cup
Europe
Total

 Lionel Messi
Barcelona
18
—
6
—
2
26[note 1]

  Alfredo Di Stéfano
Real Madrid
14
2
2
—
—
18

 Cristiano Ronaldo
Real Madrid
9
5
4
—
—
18

 Raúl
Real Madrid
11
—
3
—
1
15

 César
Barcelona
12
2
—
—
—
14

 Francisco Gento
Real Madrid
10
2
—
—
2
14

  Ferenc Puskás
Real Madrid
9
2
—
—
3
14

 Santillana
Real Madrid
9
2
—
1
—
12

 Hugo Sánchez
Real Madrid
8
—
2
—
—
10

 Juanito
Real Madrid
8
—
—
2
—
10

 Josep Samitier
Barca / Real
4
6
—
—
—
10

 Estanislao Basora
Barcelona
8
1
—
—
—
9

 Jaime Lazcano
Real Madrid
8
—
—
—
—
8

 Karim Benzema
Real Madrid
6
1
1
—
—
8

 Iván Zamorano
Real Madrid
4
2
2
—
—
8

 Eulogio Martínez
Barcelona
2
5
—
—
1
8

 Luis Suárez
Barcelona
2
4
—
—
2
8

 Santiago Bernabéu
Real Madrid
—
8
—
—
—
8

text: Consecutive goalscoring

text:
Player
Club
Consecutive matches
Total goals in the run
Start
End

 Cristiano Ronaldo
Real Madrid
6
7
2011–12 Copa del Rey (1st leg)
2012–13 La Liga (7th round)

 Iván Zamorano
Real Madrid
5
5
1992–93 La Liga (20th Round)
1993 Supercopa de España (2nd leg)

 Simón Lecue
Real Madrid
4
5
1935–36 La Liga (7th Round)
1939–40 La Liga (9th Round)

 Ronaldinho
Barcelona
4
5
2004–05 La Liga (12th Round)
2005–06 La Liga (31st Round)

 Giovanni
Barcelona
4
4
1997 Supercopa de España (1st leg)
1997–98 La Liga (28th Round)

text: Most hat-tricks

text: Five players have been able to score more than one hat trick: Jaime Lazcano, Santiago Bernabéu, Paulino Alcántara, Lionel Messi and Ferenc Puskás have all scored two hat-tricks in El Clásico history (2).

text: Most assists

text: Lionel Messi has delivered the most assists in El Clásico history (14).[61]

text: Most appearances

text: Players in bold are still active

text:
Appearances
Player
Club

43
Manuel Sanchís
Real Madrid

42
Francisco Gento
Real Madrid

42
Xavi
Barcelona

38
Lionel Messi
Barcelona

38
Sergio Ramos
Real Madrid

38
Andrés Iniesta
Barcelona

37
Fernando Hierro
Real Madrid

37
Raúl
Real Madrid

37
Iker Casillas
Real Madrid

text: Players who played for both clubs

text:
1902:  Alfonso Albéniz
1906:  José Quirante
1911:  Alfonso Albéniz
1911:  Arsenio Comamala
1913:  Walter Rozitsky
1930:  Ricardo Zamora (via Espanyol)
1932:  Josep Samitier
1950:  Alfonso Navarro
1961:  Justo Tejada
1962:  Evaristo
1965:  Fernand Goyvaerts
1988:  Bernd Schuster
1990:  Luis Milla
1992:  Nando
1994:  Michael Laudrup
1995:  Miquel Soler (via Sevilla)
2000:  Luís Figo
2000:  Albert Celades (via Celta Vigo)
2002:  Ronaldo (via Inter Milan)
2007:  Javier Saviola

text:
1905:  Luciano Lizarraga
1939:  Hilario (via Valencia)
1961:  Jesús María Pereda (via Real Valladolid, then Sevilla)
1965:  Lucien Muller
1980:  Lorenzo Amador (via Hércules)
1994:  Gheorghe Hagi (via Brescia)
1994:  Julen Lopetegui (via Logroñés)
1995:  Robert Prosinečki (via Real Oviedo)
1996:  Luis Enrique
1999:  Dani García (via Mallorca)
2000:  Alfonso Pérez (via Real Betis)
2004:  Samuel Eto'o (via Mallorca)

text:
From Barcelona to Madrid
16

From Barcelona to another club before Madrid
4

Total
20

From Madrid to Barcelona
3

From Madrid to another club before Barcelona
9

Total
12

Total Switches
32

text: Honours

text: The rivalry reflected in El Clásico matches comes about as Real Madrid and Barcelona are the most successful football clubs in Spain. As seen below, Barcelona leads Real Madrid 94–91 in terms of official overall trophies.[62] While the Inter-Cities Fairs Cup is recognised as the predecessor to the UEFA Cup, it was not organised by UEFA. Consequently, UEFA does not consider clubs' records in the Fairs Cup to be part of their European record.[63] However, FIFA does view the competition as a major honour.[64]

text:
Real Madrid
Competition
Barcelona

Domestic

33
La Liga
25

19
Copa del Rey
30

10
Supercopa de España
12

1
Copa Eva Duarte (defunct)
3

1
Copa de la Liga (defunct)
2

64
Aggregate
72

European and Worldwide

13
UEFA Champions League
5

—
UEFA Cup Winners' Cup (defunct)
4

2
UEFA Europa League
—

4
UEFA Super Cup
5

—
Inter-Cities Fairs Cup (defunct)
3

3
Intercontinental Cup (defunct)
—

2
Latin Cup (defunct)
2

3
FIFA Club World Cup
3

27
Aggregate
22

91
Total Aggregate
94

text: Note: FIFA recognized the winner of the Intercontinental Cup as a World Champion.

text: Note: The Inter-Cities Fairs Cup is not recognized in the UEFA records and statistics


document_title: The Four: Battle for Stardom

question_text: who won the four battle for stardom season 1 episode 6

root

text: The Four: Battle for Stardom

text: Format[edit]

text: The Four is a singing competition that differs among similar talent competitions, in that there are no stage auditions. The artists, also known as the challengers, are held in the holding room before singing in front of a live studio audience and the judges. The panel of people in the music industry ultimately decides the best challengers that compete against "The Four". Their decision must be unanimous. The members consist of vocalists of varying genres, and they must win challenges against new artists to keep their seat and remain as a member of "The Four". At the end of six weeks, the last singer standing among "The Four" wins the competition.

tag: p

text: There are two distinct rounds in The Four. In the performances round, new challengers must earn their seat by performing in front of a live studio audience, the panel of judges and "The Four". After the performance, the judges then vote and make a "Yes" or "No" decision, signifying the challenger's fate in the competition. If a challenger receives a unanimous four blue rings on stage (four "Yes" votes from the panel), they advance to the next round of the competition. A red ring given to the challenger signifies a "No", ending his or her time in the competition. Artists who advance to the challenge round can compete against a member of "The Four" for their seat. In a sing-off-style battle, the challenger and "The Four" member sing against each other for their seat. After the challenge, the studio audience then votes to decide which of the two should remain in the competition. The winner locks his or her seat for the rest of the night and cannot be challenged again until the next episode.[5]

text: Series overview[edit]

text:
Season

First aired

Last aired

Winner

Runner-up

Other finalists

Presenter

Panelists

1

January 4, 2018

February 8, 2018

Evvie McKinney

Candice Boyd

Vincint Cannady

Fergie

Sean Combs

Meghan Trainor

DJ Khaled

Charlie Walk1

Zhavia

2

June 7, 2018

TBA

TBD

TBD

TBD

N/A

TBD

tag: table

text: ^ Walk withdrew from the show following episode 5.

tag: ol

text: Season synopses[edit]

text: Names in bold type indicate the winner of the season.

text: Season 1[edit]

text: The first season of The Four premiered on January 4, 2018, and concluded on February 8, 2018. After six episodes, Evvie was announced as the winner of the season, with Candice Boyd as the runner-up. Along with the former and latter, the final group of "The Four" included Vincint Cannady and Zhavia.

text:
The Four

Episode

Group

Members

Seat 1

Seat 2

Seat 3

Seat 4

1

Original Four

Lex Lu

Ash Minor

Elanese Lansen

Blair Perkins

2nd Four

Zhavia

Saeed Renaud

2

3rd Four

Cheyenne Elliot

Candice Boyd

Jason Warrior

3

4th Four

Rell Jerv

Tim Johnson Jr.

4

5th Four

Nick Harrison

Kendyle Paige

5.1

6th Four

Evvie McKinney

Vincint Cannady

5.2

Final Four

Candice Boyd

Zhavia

6

text: Season 2[edit]

text: Season two of The Four premiered on June 7, 2018, and will consist of ten episodes. The first members of The Four were announced on May 9, 2018. They include Carvena Jones, James Graham,  Sharaya J, and Stephanie Zelaya.[13]

text:
The Four

Episode

Group

Members

Seat 1

Seat 2

Seat 3

Seat 4

1

Original Four

Carvena Jones

James Graham

Stephanie Zelaya

Sharaya J

2nd Four

Majeste Pearson

2

3rd Four

Jesse Kramer

Whitney Reign

3

4th Four

4

5th Four

Ali Caldwell

5

6th Four

Noah Barlass

6

7th Four

7.1

8th Four

7.2

Final Four

8

text: Reception[edit]

text: Awards and nominations[edit]

text:
Year

Award

Category

Nominee

Result

2018

Teen Choice Awards

Choice TV Series: Reality

The Four: Battle for Stardom

Pending

Choice TV Personality

DJ Khaled

Pending

Meghan Trainor

Pending

text: Ratings[edit]

text: The first season of The Four was Fox's most watched and highest-rated new unscripted series in nearly four years.[1]

text:
Season

Timeslot (ET)

# Ep.

Premiered

Ended

TV season

Season ranking

Viewers(in millions)

Date

Premiere viewers(in millions)

Date

Finale viewers(in millions)

1

Thursday8:00 PM

6

January 4, 2018

3.75[14]

February 8, 2018

4.03[15]

2017–18

117

4.19[16]

2

8

June 7, 2018

2.43[17]


document_title: Central Public Works Department, India

question_text: who started the public works department in india 1848

text: Central Public Works Department, India

text:
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text: The Central Public Works Department of India (Hindi: केंद्रीय लोक निर्माण विभाग), commonly referred to as the CPWD, is a central government owned authority in charge of public sector works. The Central Public Works Department, under the Ministry of Urban Development Now MoHUA (Ministry of Housing and Urban Affairs), builds and maintains public buildings. CPWD came into existence in July 1854 when Lord Dalhousie established a central agency for execution of public works and set up Ajmer Provincial Division. It has now grown into a comprehensive construction management department, which provides services from project concept to completion, and maintenance management.

text: It is headed by the Director General (DG) who is also the Principal Technical Advisor to the Government of India. The incumbent DG is Mr. Abhai Sinha.The regions and sub-regions are headed by Special DGs and Additional DGs respectively, while the zones in all state capitals (except a few) are headed by Chief Engineers. Now A Days, a new post of Chief Project Manager (CPM) has been created to head major prestigious projects of CPWD. CPMs are equivalent to the rank of Chief Engineers in CPWD. With country wide presence, the strength of CPWD is its ability to undertake construction of Complex Projects even in difficult terrains and maintenance in post construction stage.[1]

text: It is the prime engineering department of Government of union of India and its specifications and manuals are followed by local public works departments and engineering wing of other departments.

text: CPWD consists of three wings in execution field:

text: 1) B&R (Buildings and Roads)

text: 2) E&M (Electrical and Mechanical)

text: 3) Horticlture

text: There are three cadres in CPWD:

text: 1) CAS (Central Architecture Services)

text: 2) CES (Central Engineering Services) (केन्द्रिय अभियंत्रिकी सेवाएं)-for Civil Engineers

text: 3) CEMES (Central Electrical and Mechanical Engineering Services) (केन्द्रिय विधुत एवं यात्रिकी अभियंत्रिकी सेवाएं)-for Mechanical & Electrical Engineers

text: These are Group A Civil Services. (List of all Group A Civil Services: Civil Services of India)

text: The recruitment as entry level for middle management is made through Architecture Services Examination and Engineering Services Examination conducted by Union Public Service Commission. Only top candidates in ESE get a chance to join CPWD strictly on merit basis. During probation period, the selected candidates undergo rigorous training of 35 weeks at National CPWD Academy situated in Ghaziabad (U.P). which transforms them into competent Architects/Engineers cum bureaucrats. During the normal career progression one rises to Chief Architect/Engineer, then to Additional Director General and further to Special Director General. There is one post of Director General, CPWD who also acts as technical advisor to the Government of India.

text: The job in CPWD is challenging yet rewarding. With pan India presence, CPWD has been involved in construction of strategically important mega projects all over the country including border areas. CPWD is well known for quality construction and timely completion of projects following which it has huge list of successful projects and departments as well as clients which it has served.

text: History[edit]

text: Centralized public works in India can be traced to efforts of Lord Dalhousie and Sir Arthur Cotton in the mid 19th century. Sir Arthur Cotton sums up the early policy of the East India Company rulers thus,[2][3]

text: Public works have been almost entirely neglected throughout India. The motto hitherto has been: Do nothing, have nothing done, let nobody do anything. Bear any loss, let the people die of famine, let hundreds of lakhs be lost in revenue for want of water or roads, rather than do anything.

text: – Arthur Cotton (1854)[2]

text: Lord Dalhousie established the Central Public Works Department, and irrigation projects were among the earliest to be started.[4]

text: Public Works Department was formally established in the year 1854 in the sixth year of Lord Dalhousie’s tenure as Governor General. In the minutes of meeting held on 12 July 1854 the Governor General resolved that a central agency be provided by creating an office of Secretary to the Government of India in Department of Public Works. The note recorded by Lord Dalhousie was as under:

text: “The organization of the Department of Public Works in the Indian Empire will be incomplete unless it shall be provided for the Supreme Government itself come agency by which it may be enabled to exercise the universal control confided to it over public works in India with the best of scientific knowledge with authority and system. The Government of India shall no longer be dependent on expedients, but should be provided with a permanent and highly qualified agency to assist in the direction of this important branch of public affairs. I have, therefore, now to propose that such an agency should be provided by creating an office of the Secretary to Government of India in the Department of Public Works. The person who holds it should always be a highly qualified officer of the Corps of Engineers.”

text: Colonel W.E. Baker of the Bengal Engineers was accordingly appointed first Secretary to the Department of Public Works, this is the genesis of the Central Public Works Department.[5]

text: State Public Works Departments in India[edit]

text:
Karnataka Public Works Department
Kerala Public Works Department
Tamil Nadu Public Works Department
Uttar Pradesh Public Works Department
Maharashtra Public Works Department
Roads and Buildings Department, Gujarat
Delhi Public Works Department
Madhya PradeshPublic works department

tag: ul


document_title: List of Governors of Reserve Bank of India

question_text: who is the governor of rbi in present

question_tokens: who is the governor of rbi in present

text:
Governor of Reserve Bank of India
IncumbentUrjit Patelsince 4 September 2016Appointer
Government of IndiaInaugural holder
Osborne SmithFormation
1 April 1935

text: The Governor of the Reserve Bank of India is the chief executive of India's central bank and the ex-officio chairperson of its Central Board of Directors. Indian Rupee currency notes, issued by the Reserve Bank of India (RBI), bear the governor's signature. Since its establishment in 1935 by the British colonial government, the RBI has been headed by 24 governors. The term of office typically runs for 3 years.

text: The inaugural officeholder was the British banker Osborne Smith, while C. D. Deshmukh was the first Indian governor. The bank's 15th governor, Manmohan Singh, later became India's 13th prime minister. The position is currently held by Urjit Patel, who took over from Raghuram Rajan on 4 September 2016.

text: RBI governors[edit]

text:
No.

Name

Term of office

Began

Ended

Length

1

Osborne Smith[1]

1 April 1935

30 June 1937

7002821000000000000♠2 years, 90 days

2

James Braid Taylor[2]

1 July 1937

17 February 1943

7003205700000000000♠5 years, 231 days

3

C. D. Deshmukh

11 August 1943

30 June 1949

7003215000000000000♠5 years, 323 days

4

Benegal Rama Rau

1 July 1949

14 January 1957

7003275400000000000♠7 years, 197 days

5

K. G. Ambegaonkar

14 January 1957

28 February 1957

7001450000000000000♠45 days

6

H. V. R. Iyengar

1 March 1957

28 February 1962

7003182500000000000♠4 years, 364 days

7

P. C. Bhattacharya

1 March 1962

30 June 1967

7003194700000000000♠5 years, 121 days

8

L. K. Jha

1 July 1967

3 May 1970

7003103700000000000♠2 years, 306 days

9

B. N. Adarkar

4 May 1970

15 June 1970

7001420000000000000♠42 days

10

S. Jagannathan

16 June 1970

19 May 1975

7003179800000000000♠4 years, 337 days

11

N. C. Sen Gupta

19 May 1975

19 August 1975

7001920000000000000♠92 days

12

K. R. Puri

20 August 1975

2 May 1977

7002621000000000000♠1 year, 255 days

13

M. Narasimham

3 May 1977

30 November 1977

7002211000000000000♠211 days

14

I. G. Patel

1 December 1977

15 September 1982

7003174900000000000♠4 years, 288 days

15

Manmohan Singh

16 September 1982

14 January 1985

7002851000000000000♠2 years, 120 days

16

Amitav Ghosh

15 January 1985

4 February 1985

7001200000000000000♠20 days

17

R. N. Malhotra

4 February 1985

22 December 1990

7003214700000000000♠5 years, 321 days

18

S. Venkitaramanan

22 December 1990

21 December 1992

7002730000000000000♠1 year, 365 days

19

C. Rangarajan

22 December 1992

21 November 1997

7003179500000000000♠4 years, 334 days

20

Bimal Jalan

22 November 1997

6 September 2003

7003211400000000000♠5 years, 288 days

21

Y. V. Reddy

6 September 2003

5 September 2008

7003182600000000000♠4 years, 365 days

22

D. Subbarao

5 September 2008

4 September 2013

5 years

23

Raghuram Rajan

4 September 2013

4 September 2016

7003109600000000000♠3 years, 0 days

24

Urjit Patel

4 September 2016

Incumbent

7002782000000000000♠2 years, 52 days


document_title: Sun

question_text: temperature of the surface of the sun in kelvin

question_tokens: temperature of the surface of the sun in kelvin

text: Sun

text: Name and etymology

text: The English proper name Sun developed from Old English sunne and may be related to south. Cognates to English sun appear in other Germanic languages, including Old Frisian sunne, sonne, Old Saxon sunna, Middle Dutch sonne, modern Dutch zon, Old High German sunna, modern German Sonne, Old Norse sunna, and Gothic sunnō. All Germanic terms for the Sun stem from Proto-Germanic *sunnōn.[20][21]

text: The English weekday name Sunday stems from Old English (Sunnandæg; "Sun's day", from before 700) and is ultimately a result of a Germanic interpretation of Latin dies solis, itself a translation of the Greek ἡμέρα ἡλίου (hēméra hēlíou).[22] The Latin name for the Sun, Sol, is not common in general English language use; the adjectival form is the related word solar.[23][24] The term sol is also used by planetary astronomers to refer to the duration of a solar day on another planet, such as Mars.[25] A mean Earth solar day is approximately 24 hours, whereas a mean Martian 'sol' is 24 hours, 39 minutes, and 35.244 seconds.[26]

text: Religious aspects

text: Solar deities play a major role in many world religions and mythologies.[27] The ancient Sumerians believed that the sun was Utu,[28][29] the god of justice and twin brother of Inanna, the Queen of Heaven,[28] who was identified as the planet Venus.[29] Later, Utu was identified with the East Semitic god Shamash.[28][29] Utu was regarded as a helper-deity, who aided those in distress,[28] and, in iconography, he is usually portrayed with a long beard and clutching a saw,[28] which represented his role as the dispenser of justice.[28]

text: From at least the 4th Dynasty of Ancient Egypt, the Sun was worshipped as the god Ra, portrayed as a falcon-headed divinity surmounted by the solar disk, and surrounded by a serpent. In the New Empire period, the Sun became identified with the dung beetle, whose spherical ball of dung was identified with the Sun. In the form of the Sun disc Aten, the Sun had a brief resurgence during the Amarna Period when it again became the preeminent, if not only, divinity for the Pharaoh Akhenaton.[30][31]

text: In Proto-Indo-European religion, the sun was personified as the goddess *Seh2ul.[32][33][21] Derivatives of this goddess in Indo-European languages include the Old Norse Sól, Sanskrit Surya, Gaulish Sulis, Lithuanian Saulė, and Slavic Solntse.[21] In ancient Greek religion, the sun deity was the male god Helios,[32] but traces of an earlier female solar deity are preserved in Helen of Troy.[32] In later times, Helios was syncretized with Apollo.[34]

text: In the Bible, Malachi 4:2 mentions the "Sun of Righteousness" (sometimes translated as the "Sun of Justice"),[35] which some Christians have interpreted as a reference to the Messiah (Christ).[36] In ancient Roman culture, Sunday was the day of the Sun god. It was adopted as the Sabbath day by Christians who did not have a Jewish background. The symbol of light was a pagan device adopted by Christians, and perhaps the most important one that did not come from Jewish traditions. In paganism, the Sun was a source of life, giving warmth and illumination to mankind. It was the center of a popular cult among Romans, who would stand at dawn to catch the first rays of sunshine as they prayed. The celebration of the winter solstice (which influenced Christmas) was part of the Roman cult of the unconquered Sun (Sol Invictus). Christian churches were built with an orientation so that the congregation faced toward the sunrise in the East.[37]

text: Tonatiuh, the Aztec god of the sun, was usually depicted holding arrows and a shield[38] and was closely associated with the practice of human sacrifice.[38] The sun goddess Amaterasu is the most important deity in the Shinto religion,[39][40] and she is believed to be the direct ancestor of all Japanese emperors.[39]

text: Characteristics

text: The Sun is a G-type main-sequence star that comprises about 99.86% of the mass of the Solar System. The Sun has an absolute magnitude of +4.83, estimated to be brighter than about 85% of the stars in the Milky Way, most of which are red dwarfs.[41][42] The Sun is a Population I, or heavy-element-rich,[b] star.[43] The formation of the Sun may have been triggered by shockwaves from one or more nearby supernovae.[44] This is suggested by a high abundance of heavy elements in the Solar System, such as gold and uranium, relative to the abundances of these elements in so-called Population II, heavy-element-poor, stars. The heavy elements could most plausibly have been produced by endothermic nuclear reactions during a supernova, or by transmutation through neutron absorption within a massive second-generation star.[43]

text: The Sun is by far the brightest object in the Earth's sky, with an apparent magnitude of −26.74.[45][46] This is about 13 billion times brighter than the next brightest star, Sirius, which has an apparent magnitude of −1.46. The mean distance of the Sun's center to Earth's center is approximately 1 astronomical unit (about 150,000,000 km; 93,000,000 mi), though the distance varies as Earth moves from perihelion in January to aphelion in July.[47] At this average distance, light travels from the Sun's horizon to Earth's horizon in about 8 minutes and 19 seconds, while light from the closest points of the Sun and Earth takes about two seconds less. The energy of this sunlight supports almost all life[c] on Earth by photosynthesis,[48] and drives Earth's climate and weather.

text: The Sun does not have a definite boundary, but its density decreases exponentially with increasing height above the photosphere.[49] For the purpose of measurement, however, the Sun's radius is considered to be the distance from its center to the edge of the photosphere, the apparent visible surface of the Sun.[50] By this measure, the Sun is a near-perfect sphere with an oblateness estimated at about 9 millionths,[51] which means that its polar diameter differs from its equatorial diameter by only 10 kilometres (6.2 mi).[52] The tidal effect of the planets is weak and does not significantly affect the shape of the Sun.[53] The Sun rotates faster at its equator than at its poles. This differential rotation is caused by convective motion due to heat transport and the Coriolis force due to the Sun's rotation. In a frame of reference defined by the stars, the rotational period is approximately 25.6 days at the equator and 33.5 days at the poles. Viewed from Earth as it orbits the Sun, the apparent rotational period of the Sun at its equator is about 28 days.[54]

text: Sunlight

text: The solar constant is the amount of power that the Sun deposits per unit area that is directly exposed to sunlight. The solar constant is equal to approximately 7003136800000000000♠1,368 W/m2 (watts per square meter) at a distance of one astronomical unit (AU) from the Sun (that is, on or near Earth).[55] Sunlight on the surface of Earth is attenuated by Earth's atmosphere, so that less power arrives at the surface (closer to 7003100000000000000♠1,000 W/m2) in clear conditions when the Sun is near the zenith.[56] Sunlight at the top of Earth's atmosphere is composed (by total energy) of about 50% infrared light, 40% visible light, and 10% ultraviolet light.[57] The atmosphere in particular filters out over 70% of solar ultraviolet, especially at the shorter wavelengths.[58] Solar ultraviolet radiation ionizes Earth's dayside upper atmosphere, creating the electrically conducting ionosphere.[59]

text: The Sun's color is white, with a CIE color-space index near (0.3, 0.3), when viewed from space or when the Sun is high in the sky. When measuring all the photons emitted, the Sun is actually emitting more photons in the green portion of the spectrum than any other.[60][61] When the Sun is low in the sky, atmospheric scattering renders the Sun yellow, red, orange, or magenta. Despite its typical whiteness, most people mentally picture the Sun as yellow; the reasons for this are the subject of debate.[62] The Sun is a G2V star, with G2 indicating its surface temperature of approximately 5,778 K (5,505 °C, 9,941 °F), and V that it, like most stars, is a main-sequence star.[63][64] The average luminance of the Sun is about 1.88 giga candela per square metre, but as viewed through Earth's atmosphere, this is lowered to about 1.44 Gcd/m2.[d] However, the luminance is not constant across the disk of the Sun (limb darkening).

text: Composition

text: The Sun is composed primarily of the chemical elements hydrogen and helium; they account for 74.9% and 23.8% of the mass of the Sun in the photosphere, respectively.[65] All heavier elements, called metals in astronomy, account for less than 2% of the mass, with oxygen (roughly 1% of the Sun's mass), carbon (0.3%), neon (0.2%), and iron (0.2%) being the most abundant.[66]

text: The Sun inherited its chemical composition from the interstellar medium out of which it formed. The hydrogen and helium in the Sun were produced by Big Bang nucleosynthesis, and the heavier elements were produced by stellar nucleosynthesis in generations of stars that completed their stellar evolution and returned their material to the interstellar medium before the formation of the Sun.[67] The chemical composition of the photosphere is normally considered representative of the composition of the primordial Solar System.[68] However, since the Sun formed, some of the helium and heavy elements have gravitationally settled from the photosphere. Therefore, in today's photosphere the helium fraction is reduced, and the metallicity is only 84% of what it was in the protostellar phase (before nuclear fusion in the core started). The protostellar Sun's composition is believed to have been 71.1% hydrogen, 27.4% helium, and 1.5% heavier elements.[65]

text: Today, nuclear fusion in the Sun's core has modified the composition by converting hydrogen into helium, so the innermost portion of the Sun is now roughly 60% helium, with the abundance of heavier elements unchanged. Because heat is transferred from the Sun's core by radiation rather than by convection (see Radiative zone below), none of the fusion products from the core have risen to the photosphere.[69]

text: The reactive core zone of "hydrogen burning", where hydrogen is converted into helium, is starting to surround an inner core of "helium ash". This development will continue and will eventually cause the Sun to leave the main sequence, to become a red giant.[70]

text: The solar heavy-element abundances described above are typically measured both using spectroscopy of the Sun's photosphere and by measuring abundances in meteorites that have never been heated to melting temperatures. These meteorites are thought to retain the composition of the protostellar Sun and are thus not affected by settling of heavy elements. The two methods generally agree well.[18]

text: Singly ionized iron-group elements

text: In the 1970s, much research focused on the abundances of iron-group elements in the Sun.[71][72] Although significant research was done, until 1978 it was difficult to determine the abundances of some iron-group elements (e.g. cobalt and manganese) via spectrography because of their hyperfine structures.[71]

text: The first largely complete set of oscillator strengths of singly ionized iron-group elements were made available in the 1960s,[73] and these were subsequently improved.[74] In 1978, the abundances of singly ionized elements of the iron group were derived.[71]

text: Isotopic composition

text: Various authors have considered the existence of a gradient in the isotopic compositions of solar and planetary noble gases,[75] e.g. correlations between isotopic compositions of neon and xenon in the Sun and on the planets.[76]

text: Prior to 1983, it was thought that the whole Sun has the same composition as the solar atmosphere.[77] In 1983, it was claimed that it was fractionation in the Sun itself that caused the isotopic-composition relationship between the planetary and solar-wind-implanted noble gases.[77]

text: Structure and energy production

text: Core

text: The core of the Sun extends from the center to about 20–25% of the solar radius.[78] It has a density of up to 7005150000000000000♠150 g/cm3[79][80] (about 150 times the density of water) and a temperature of close to 15.7 million kelvins (K).[80] By contrast, the Sun's surface temperature is approximately 5,800 K. Recent analysis of SOHO mission data favors a faster rotation rate in the core than in the radiative zone above.[78] Through most of the Sun's life, energy has been produced by nuclear fusion in the core region through a series of steps called the p–p (proton–proton) chain; this process converts hydrogen into helium.[81] Only 0.8% of the energy generated in the Sun comes from the CNO cycle, though this proportion is expected to increase as the Sun becomes older.[82]

text: The core is the only region in the Sun that produces an appreciable amount of thermal energy through fusion; 99% of the power is generated within 24% of the Sun's radius, and by 30% of the radius, fusion has stopped nearly entirely. The remainder of the Sun is heated by this energy as it is transferred outwards through many successive layers, finally to the solar photosphere where it escapes into space as sunlight or the kinetic energy of particles.[63][83]

text: The proton–proton chain occurs around 7037919999999999999♠9.2×1037 times each second in the core, converting about 3.7×1038 protons into alpha particles (helium nuclei) every second (out of a total of ~8.9×1056 free protons in the Sun), or about 6.2×1011 kg/s.[63] Fusing four free protons (hydrogen nuclei) into a single alpha particle (helium nucleus) releases around 0.7% of the fused mass as energy,[84] so the Sun releases energy at the mass–energy conversion rate of 4.26 million metric tons per second (which requires 600 metric megatons of hydrogen [85]), for 384.6 yottawatts (7026384600000000000♠3.846×1026 W),[1] or 9.192×1010 megatons of TNT per second. Theoretical models of the Sun's interior indicate a power density of approximately 276.5 W/m3,[86] a value that more nearly approximates that of reptile metabolism or a compost pile[87] than of a thermonuclear bomb.[e]

text: The fusion rate in the core is in a self-correcting equilibrium: a slightly higher rate of fusion would cause the core to heat up more and expand slightly against the weight of the outer layers, reducing the density and hence the fusion rate and correcting the perturbation; and a slightly lower rate would cause the core to cool and shrink slightly, increasing the density and increasing the fusion rate and again reverting it to its present rate.[88][89]

text: Radiative zone

text: From the core out to about 0.7 solar radii, thermal radiation is the primary means of energy transfer.[90] The temperature drops from approximately 7 million to 2 million kelvins with increasing distance from the core.[80] This temperature gradient is less than the value of the adiabatic lapse rate and hence cannot drive convection, which explains why the transfer of energy through this zone is by radiation instead of thermal convection.[80] Ions of hydrogen and helium emit photons, which travel only a brief distance before being reabsorbed by other ions.[90] The density drops a hundredfold (from 20 g/cm3 to 0.2 g/cm3) from 0.25 solar radii to the 0.7 radii, the top of the radiative zone.[90]

text: Tachocline

text: The radiative zone and the convective zone are separated by a transition layer, the tachocline. This is a region where the sharp regime change between the uniform rotation of the radiative zone and the differential rotation of the convection zone results in a large shear between the two—a condition where successive horizontal layers slide past one another.[91] Presently, it is hypothesized (see Solar dynamo) that a magnetic dynamo within this layer generates the Sun's magnetic field.[80]

text: Convective zone

text: The Sun's convection zone extends from 0.7 solar radii (500,000 km) to near the surface. In this layer, the solar plasma is not dense enough or hot enough to transfer the heat energy of the interior outward via radiation. Instead, the density of the plasma is low enough to allow convective currents to develop and move the Sun's energy outward towards its surface. Material heated at the tachocline picks up heat and expands, thereby reducing its density and allowing it to rise. As a result, an orderly motion of the mass develops into thermal cells that carry the majority of the heat outward to the Sun's photosphere above. Once the material diffusively and radiatively cools just beneath the photospheric surface, its density increases, and it sinks to the base of the convection zone, where it again picks up heat from the top of the radiative zone and the convective cycle continues. At the photosphere, the temperature has dropped to 5,700 K and the density to only 0.2 g/m3 (about 1/6,000 the density of air at sea level).[80]

text: The thermal columns of the convection zone form an imprint on the surface of the Sun giving it a granular appearance called the solar granulation at the smallest scale and supergranulation at larger scales. Turbulent convection in this outer part of the solar interior sustains "small-scale" dynamo action over the near-surface volume of the Sun.[80] The Sun's thermal columns are Bénard cells and take the shape of hexagonal prisms.[92]

text: Photosphere

text: The visible surface of the Sun, the photosphere, is the layer below which the Sun becomes opaque to visible light.[93] Above the photosphere visible sunlight is free to propagate into space, and almost all of its energy escapes the Sun entirely. The change in opacity is due to the decreasing amount of H− ions, which absorb visible light easily.[93] Conversely, the visible light we see is produced as electrons react with hydrogen atoms to produce H− ions.[94][95] The photosphere is tens to hundreds of kilometers thick, and is slightly less opaque than air on Earth. Because the upper part of the photosphere is cooler than the lower part, an image of the Sun appears brighter in the center than on the edge or limb of the solar disk, in a phenomenon known as limb darkening.[93] The spectrum of sunlight has approximately the spectrum of a black-body radiating at about 6,000 K, interspersed with atomic absorption lines from the tenuous layers above the photosphere. The photosphere has a particle density of ~1023 m−3 (about 0.37% of the particle number per volume of Earth's atmosphere at sea level). The photosphere is not fully ionized—the extent of ionization is about 3%, leaving almost all of the hydrogen in atomic form.[96]

text: During early studies of the optical spectrum of the photosphere, some absorption lines were found that did not correspond to any chemical elements then known on Earth. In 1868, Norman Lockyer hypothesized that these absorption lines were caused by a new element that he dubbed helium, after the Greek Sun god Helios. Twenty-five years later, helium was isolated on Earth.[97]

text: Atmosphere

text: During a total solar eclipse, when the disk of the Sun is covered by that of the Moon, parts of the Sun's surrounding atmosphere can be seen. It is composed of four distinct parts: the chromosphere, the transition region, the corona and the heliosphere.

text: The coolest layer of the Sun is a temperature minimum region extending to about 7005500000000000000♠500 km above the photosphere, and has a temperature of about 7003410000000000000♠4,100 K.[93] This part of the Sun is cool enough to allow the existence of simple molecules such as carbon monoxide and water, which can be detected via their absorption spectra.[98]

text: The chromosphere, transition region, and corona are much hotter than the surface of the Sun.[93] The reason is not well understood, but evidence suggests that Alfvén waves may have enough energy to heat the corona.[99]

text: Above the temperature minimum layer is a layer about 7006200000000000000♠2,000 km thick, dominated by a spectrum of emission and absorption lines.[93] It is called the chromosphere from the Greek root chroma, meaning color, because the chromosphere is visible as a colored flash at the beginning and end of total solar eclipses.[90] The temperature of the chromosphere increases gradually with altitude, ranging up to around 7004200000000000000♠20,000 K near the top.[93] In the upper part of the chromosphere helium becomes partially ionized.[100]

text: Above the chromosphere, in a thin (about 200 km) transition region, the temperature rises rapidly from around 20,000 K in the upper chromosphere to coronal temperatures closer to 1,000,000 K.[101] The temperature increase is facilitated by the full ionization of helium in the transition region, which significantly reduces radiative cooling of the plasma.[100] The transition region does not occur at a well-defined altitude. Rather, it forms a kind of nimbus around chromospheric features such as spicules and filaments, and is in constant, chaotic motion.[90] The transition region is not easily visible from Earth's surface, but is readily observable from space by instruments sensitive to the extreme ultraviolet portion of the spectrum.[102]

text: The corona is the next layer of the Sun. The low corona, near the surface of the Sun, has a particle density around 1015 m−3 to 1016 m−3.[100][f] The average temperature of the corona and solar wind is about 1,000,000–2,000,000 K; however, in the hottest regions it is 8,000,000–20,000,000 K.[101] Although no complete theory yet exists to account for the temperature of the corona, at least some of its heat is known to be from magnetic reconnection.[101][103] The corona is the extended atmosphere of the Sun, which has a volume much larger than the volume enclosed by the Sun's photosphere. A flow of plasma outward from the Sun into interplanetary space is the solar wind.[103]

text: The heliosphere, the tenuous outermost atmosphere of the Sun, is filled with the solar wind plasma. This outermost layer of the Sun is defined to begin at the distance where the flow of the solar wind becomes superalfvénic—that is, where the flow becomes faster than the speed of Alfvén waves,[104] at approximately 20 solar radii (0.1 AU). Turbulence and dynamic forces in the heliosphere cannot affect the shape of the solar corona within, because the information can only travel at the speed of Alfvén waves. The solar wind travels outward continuously through the heliosphere,[105][106] forming the solar magnetic field into a spiral shape,[103] until it impacts the heliopause more than 50 AU from the Sun. In December 2004, the Voyager 1 probe passed through a shock front that is thought to be part of the heliopause.[107] In late 2012 Voyager 1 recorded a marked increase in cosmic ray collisions and a sharp drop in lower energy particles from the solar wind, which suggested that the probe had passed through the heliopause and entered the interstellar medium.[108]

text: Photons and neutrinos

text: High-energy gamma-ray photons initially released with fusion reactions in the core are almost immediately absorbed by the solar plasma of the radiative zone, usually after traveling only a few millimeters. Re-emission happens in a random direction and usually at a slightly lower energy. With this sequence of emissions and absorptions, it takes a long time for radiation to reach the Sun's surface. Estimates of the photon travel time range between 10,000 and 170,000 years.[109] In contrast, it takes only 2.3 seconds for the neutrinos, which account for about 2% of the total energy production of the Sun, to reach the surface. Because energy transport in the Sun is a process that involves photons in thermodynamic equilibrium with matter, the time scale of energy transport in the Sun is longer, on the order of 30,000,000 years. This is the time it would take the Sun to return to a stable state, if the rate of energy generation in its core were suddenly changed.[110]

text: Neutrinos are also released by the fusion reactions in the core, but, unlike photons, they rarely interact with matter, so almost all are able to escape the Sun immediately. For many years measurements of the number of neutrinos produced in the Sun were lower than theories predicted by a factor of 3. This discrepancy was resolved in 2001 through the discovery of the effects of neutrino oscillation: the Sun emits the number of neutrinos predicted by the theory, but neutrino detectors were missing 2⁄3 of them because the neutrinos had changed flavor by the time they were detected.[111]

text: Magnetism and activity

text: Magnetic field

text: The Sun has a magnetic field that varies across the surface of the Sun. Its polar field is 1–2 gauss (0.0001–0.0002 T), whereas the field is typically 3,000 gauss (0.3 T) in features on the Sun called sunspots and 10–100 gauss (0.001–0.01 T) in solar prominences.[1]

text: The magnetic field also varies in time and location. The quasi-periodic 11-year solar cycle is the most prominent variation in which the number and size of sunspots waxes and wanes.[16][113][114]

text: Sunspots are visible as dark patches on the Sun's photosphere, and correspond to concentrations of magnetic field where the convective transport of heat is inhibited from the solar interior to the surface. As a result, sunspots are slightly cooler than the surrounding photosphere, and, so, they appear dark. At a typical solar minimum, few sunspots are visible, and occasionally none can be seen at all. Those that do appear are at high solar latitudes. As the solar cycle progresses towards its maximum, sunspots tend form closer to the solar equator, a phenomenon known as Spörer's law. The largest sunspots can be tens of thousands of kilometers across.[115]

text: An 11-year sunspot cycle is half of a 22-year Babcock–Leighton dynamo cycle, which corresponds to an oscillatory exchange of energy between toroidal and poloidal solar magnetic fields. At solar-cycle maximum, the external poloidal dipolar magnetic field is near its dynamo-cycle minimum strength, but an internal toroidal quadrupolar field, generated through differential rotation within the tachocline, is near its maximum strength. At this point in the dynamo cycle, buoyant upwelling within the convective zone forces emergence of toroidal magnetic field through the photosphere, giving rise to pairs of sunspots, roughly aligned east–west and having footprints with opposite magnetic polarities. The magnetic polarity of sunspot pairs alternates every solar cycle, a phenomenon known as the Hale cycle.[116][117]

text: During the solar cycle's declining phase, energy shifts from the internal toroidal magnetic field to the external poloidal field, and sunspots diminish in number and size. At solar-cycle minimum, the toroidal field is, correspondingly, at minimum strength, sunspots are relatively rare, and the poloidal field is at its maximum strength. With the rise of the next 11-year sunspot cycle, differential rotation shifts magnetic energy back from the poloidal to the toroidal field, but with a polarity that is opposite to the previous cycle. The process carries on continuously, and in an idealized, simplified scenario, each 11-year sunspot cycle corresponds to a change, then, in the overall polarity of the Sun's large-scale magnetic field.[118][119]

text: The solar magnetic field extends well beyond the Sun itself. The electrically conducting solar wind plasma carries the Sun's magnetic field into space, forming what is called the interplanetary magnetic field.[103] In an approximation known as ideal magnetohydrodynamics, plasma particles only move along the magnetic field lines. As a result, the outward-flowing solar wind stretches the interplanetary magnetic field outward, forcing it into a roughly radial structure. For a simple dipolar solar magnetic field, with opposite hemispherical polarities on either side of the solar magnetic equator, a thin current sheet is formed in the solar wind.[103] At great distances, the rotation of the Sun twists the dipolar magnetic field and corresponding current sheet into an Archimedean spiral structure called the Parker spiral.[103] The interplanetary magnetic field is much stronger than the dipole component of the solar magnetic field. The Sun's dipole magnetic field of 50–400 μT (at the photosphere) reduces with the inverse-cube of the distance to about 0.1 nT at the distance of Earth. However, according to spacecraft observations the interplanetary field at Earth's location is around 5 nT, about a hundred times greater.[120] The difference is due to magnetic fields generated by electrical currents in the plasma surrounding the Sun.

text: Variation in activity

text: The Sun's magnetic field leads to many effects that are collectively called solar activity. Solar flares and coronal-mass ejections tend to occur at sunspot groups. Slowly changing high-speed streams of solar wind are emitted from coronal holes at the photospheric surface. Both coronal-mass ejections and high-speed streams of solar wind carry plasma and interplanetary magnetic field outward into the Solar System.[121] The effects of solar activity on Earth include auroras at moderate to high latitudes and the disruption of radio communications and electric power. Solar activity is thought to have played a large role in the formation and evolution of the Solar System.

text: With solar-cycle modulation of sunspot number comes a corresponding modulation of space weather conditions, including those surrounding Earth where technological systems can be affected.

text: Long-term change

text: Long-term secular change in sunspot number is thought, by some scientists, to be correlated with long-term change in solar irradiance,[122] which, in turn, might influence Earth's long-term climate.[123] For example, in the 17th century, the solar cycle appeared to have stopped entirely for several decades; few sunspots were observed during a period known as the Maunder minimum. This coincided in time with the era of the Little Ice Age, when Europe experienced unusually cold temperatures.[124] Earlier extended minima have been discovered through analysis of tree rings and appear to have coincided with lower-than-average global temperatures.[125]

text: A recent theory claims that there are magnetic instabilities in the core of the Sun that cause fluctuations with periods of either 41,000 or 100,000 years. These could provide a better explanation of the ice ages than the Milankovitch cycles.[126][127]

text: Life phases

text: The Sun today is roughly halfway through the most stable part of its life. It has not changed dramatically for over four billion[a] years, and will remain fairly stable for more than five billion more. However, after hydrogen fusion in its core has stopped, the Sun will undergo severe changes, both internally and externally.

text: Formation

text: The Sun formed about 4.6 billion years ago from the collapse of part of a giant molecular cloud that consisted mostly of hydrogen and helium and that probably gave birth to many other stars.[128] This age is estimated using computer models of stellar evolution and through nucleocosmochronology.[10] The result is consistent with the radiometric date of the oldest Solar System material, at 4.567 billion years ago.[129][130] Studies of ancient meteorites reveal traces of stable daughter nuclei of short-lived isotopes, such as iron-60, that form only in exploding, short-lived stars. This indicates that one or more supernovae must have occurred near the location where the Sun formed. A shock wave from a nearby supernova would have triggered the formation of the Sun by compressing the matter within the molecular cloud and causing certain regions to collapse under their own gravity.[131] As one fragment of the cloud collapsed it also began to rotate because of conservation of angular momentum and heat up with the increasing pressure. Much of the mass became concentrated in the center, whereas the rest flattened out into a disk that would become the planets and other Solar System bodies. Gravity and pressure within the core of the cloud generated a lot of heat as it accreted more matter from the surrounding disk, eventually triggering nuclear fusion. Thus, the Sun was born.

text: Main sequence

text: The Sun is about halfway through its main-sequence stage, during which nuclear fusion reactions in its core fuse hydrogen into helium. Each second, more than four million tonnes of matter are converted into energy within the Sun's core, producing neutrinos and solar radiation. At this rate, the Sun has so far converted around 100 times the mass of Earth into energy, about 0.03% of the total mass of the Sun. The Sun will spend a total of approximately 10 billion years as a main-sequence star.[133] The Sun is gradually becoming hotter during its time on the main sequence, because the helium atoms in the core occupy less volume than the hydrogen atoms that were fused. The core is therefore shrinking, allowing the outer layers of the Sun to move closer to the centre and experience a stronger gravitational force, according to the inverse-square law. This stronger force increases the pressure on the core, which is resisted by a gradual increase in the rate at which fusion occurs. This process speeds up as the core gradually becomes denser. It is estimated that the Sun has become 30% brighter in the last 4.5 billion years.[134] At present, it is increasing in brightness by about 1% every 100 million years.[135]

text: After core hydrogen exhaustion

text: The Sun does not have enough mass to explode as a supernova. Instead it will exit the main sequence in approximately 5 billion years and start to turn into a red giant.[136][137] As a red giant, the Sun will grow so large that it will engulf Mercury, Venus, and probably Earth.[137][138]

text: Even before it becomes a red giant, the luminosity of the Sun will have nearly doubled, and Earth will receive as much sunlight as Venus receives today. Once the core hydrogen is exhausted in 5.4 billion years, the Sun will expand into a subgiant phase and slowly double in size over about half a billion years. It will then expand more rapidly over about half a billion years until it is over two hundred times larger than today and a couple of thousand times more luminous. This then starts the red-giant-branch phase where the Sun will spend around a billion years and lose around a third of its mass.[137]

text: After the red-giant branch the Sun has approximately 120 million years of active life left, but much happens. First, the core, full of degenerate helium ignites violently in the helium flash, where it is estimated that 6% of the core, itself 40% of the Sun's mass, will be converted into carbon within a matter of minutes through the triple-alpha process.[139] The Sun then shrinks to around 10 times its current size and 50 times the luminosity, with a temperature a little lower than today. It will then have reached the red clump or horizontal branch, but a star of the Sun's mass does not evolve blueward along the horizontal branch. Instead, it just becomes moderately larger and more luminous over about 100 million years as it continues to burn helium in the core.[137]

text: When the helium is exhausted, the Sun will repeat the expansion it followed when the hydrogen in the core was exhausted, except that this time it all happens faster, and the Sun becomes larger and more luminous. This is the asymptotic-giant-branch phase, and the Sun is alternately burning hydrogen in a shell or helium in a deeper shell. After about 20 million years on the early asymptotic giant branch, the Sun becomes increasingly unstable, with rapid mass loss and thermal pulses that increase the size and luminosity for a few hundred years every 100,000 years or so. The thermal pulses become larger each time, with the later pulses pushing the luminosity to as much as 5,000 times the current level and the radius to over 1 AU.[140] According to a 2008 model, Earth's orbit is shrinking due to tidal forces (and, eventually, drag from the lower chromosphere), so that it will be engulfed by the Sun near the tip of the red giant branch phase, 1 and 3.8 million years after Mercury and Venus have respectively suffered the same fate. Models vary depending on the rate and timing of mass loss. Models that have higher mass loss on the red-giant branch produce smaller, less luminous stars at the tip of the asymptotic giant branch, perhaps only 2,000 times the luminosity and less than 200 times the radius.[137] For the Sun, four thermal pulses are predicted before it completely loses its outer envelope and starts to make a planetary nebula. By the end of that phase – lasting approximately 500,000 years – the Sun will only have about half of its current mass.

text: The post-asymptotic-giant-branch evolution is even faster. The luminosity stays approximately constant as the temperature increases, with the ejected half of the Sun's mass becoming ionised into a planetary nebula as the exposed core reaches 30,000 K. The final naked core, a white dwarf, will have a temperature of over 100,000 K, and contain an estimated 54.05% of the Sun's present day mass.[137] The planetary nebula will disperse in about 10,000 years, but the white dwarf will survive for trillions of years before fading to a hypothetical black dwarf.[141][142]

text: Motion and location

text: The Sun lies close to the inner rim of the Milky Way's Orion Arm, in the Local Interstellar Cloud or the Gould Belt, at a distance of 7.5–8.5 kpc (25,000–28,000 light-years) from the Galactic Center.[143][144] [145][146][147][148] The Sun is contained within the Local Bubble, a space of rarefied hot gas, possibly produced by the supernova remnant Geminga,[149] or multiple supernovae in subgroup B1 of the Pleiades moving group.[150] The distance between the local arm and the next arm out, the Perseus Arm, is about 6,500 light-years.[151] The Sun, and thus the Solar System, is found in what scientists call the galactic habitable zone. The Apex of the Sun's Way, or the solar apex, is the direction that the Sun travels relative to other nearby stars. This motion is towards a point in the constellation Hercules, near the star Vega. Of the 50 nearest stellar systems within 17 light-years from Earth (the closest being the red dwarf Proxima Centauri at approximately 4.2 light-years), the Sun ranks fourth in mass.[152]

text: Orbit in Milky Way

text: The Sun orbits the center of the Milky Way, and it is presently moving in the direction of the constellation of Cygnus. A simple model of the motion of a star in the galaxy gives the galactic coordinates X, Y, and Z as:

text:
where U, V, and W are the respective velocities with respect to the local standard of rest, A and B are the Oort constants,

Ω

0

=
A
−
B

{\displaystyle \Omega _{0}=A-B}

 is the angular velocity of galactic rotation for the local standard of rest,

κ
=

−
4

Ω

0

B

{\displaystyle \kappa ={\sqrt {-4\Omega _{0}B}}}

 is the "epicyclic frequency", and ν is the vertical oscillation frequency.[153] For the sun, the present values of U, V, and W are estimated as

(
U
(
0
)
,
V
(
0
)
,
W
(
0
)
)
=
(
10.00
,
5.25
,
7.17
)

{\displaystyle (U(0),V(0),W(0))=(10.00,5.25,7.17)}

 km/s, and estimates for the other constants are A = 15.5 km/s/kpc, B = −12.2 km/s/kpc, κ = 37 km/s/kpc, and ν=74 km/s/kpc. We take X(0) and Y(0) to be zero and Z(0) is estimated to be 17 parsecs.[154] This model implies that the sun circulates around a point that is itself going around the galaxy. The period of the sun's circulation around the point is

2
π

/

κ

{\displaystyle 2\pi /\kappa }

. which, using the equivalence that a parsec equals 1 km/s times 0.978 million years, comes to 166 million years, shorter than the time it takes for the point to go around the galaxy. In the (X, Y) coordinates, the sun describes an ellipse around the point, whose length in the Y direction is

text: and whose width in the X direction is

text: The moving point is presently at

text: The oscillation in the Z direction takes the sun

text:
above the galactic plane and the same distance below it, with a period of

2
π

/

ν

{\displaystyle 2\pi /\nu }

 or 83 million years, approximately 2.7 times per orbit.[155] Although

2
π

/

Ω

0

{\displaystyle 2\pi /\Omega _{0}}

 is 222 million years, the value of

Ω

{\displaystyle \Omega }

 at the point around which the sun circulates is

text:
(see Oort constants), corresponding to 235 million years, and this is the time that the point takes to go once around the galaxy. Other stars with the same value of

X
+
V

/

(
2
B
)

{\displaystyle X+V/(2B)}

 have take the same amount of time to go around the galaxy as the sun and thus remain in the same general vicinity as the sun.

text: The Sun's orbit around the Milky Way is perturbed due to the non-uniform mass distribution in Milky Way, such as that in and between the galactic spiral arms. It has been argued that the Sun's passage through the higher density spiral arms often coincides with mass extinctions on Earth, perhaps due to increased impact events.[156] It takes the Solar System about 225–250 million years to complete one orbit through the Milky Way (a galactic year),[157] so it is thought to have completed 20–25 orbits during the lifetime of the Sun. The orbital speed of the Solar System about the center of the Milky Way is approximately 251 km/s (156 mi/s).[158] At this speed, it takes around 1,190 years for the Solar System to travel a distance of 1 light-year, or 7 days to travel 1 AU.[159]

text: The Milky Way is moving with respect to the cosmic microwave background radiation (CMB) in the direction of the constellation Hydra with a speed of 550 km/s, and the Sun's resultant velocity with respect to the CMB is about 370 km/s in the direction of Crater or Leo.[160]

text: Theoretical problems

text: Coronal heating problem

text: The temperature of the photosphere is approximately 6,000 K, whereas the temperature of the corona reaches 1,000,000–2,000,000 K.[101] The high temperature of the corona shows that it is heated by something other than direct heat conduction from the photosphere.[103]

text: It is thought that the energy necessary to heat the corona is provided by turbulent motion in the convection zone below the photosphere, and two main mechanisms have been proposed to explain coronal heating.[101] The first is wave heating, in which sound, gravitational or magnetohydrodynamic waves are produced by turbulence in the convection zone.[101] These waves travel upward and dissipate in the corona, depositing their energy in the ambient matter in the form of heat.[161] The other is magnetic heating, in which magnetic energy is continuously built up by photospheric motion and released through magnetic reconnection in the form of large solar flares and myriad similar but smaller events—nanoflares.[162]

text: Currently, it is unclear whether waves are an efficient heating mechanism. All waves except Alfvén waves have been found to dissipate or refract before reaching the corona.[163] In addition, Alfvén waves do not easily dissipate in the corona. Current research focus has therefore shifted towards flare heating mechanisms.[101]

text: Faint young Sun problem

text: Theoretical models of the Sun's development suggest that 3.8 to 2.5 billion years ago, during the Archean eon, the Sun was only about 75% as bright as it is today. Such a weak star would not have been able to sustain liquid water on Earth's surface, and thus life should not have been able to develop. However, the geological record demonstrates that Earth has remained at a fairly constant temperature throughout its history, and that the young Earth was somewhat warmer than it is today. One theory among scientists is that the atmosphere of the young Earth contained much larger quantities of greenhouse gases (such as carbon dioxide, methane) than are present today, which trapped enough heat to compensate for the smaller amount of solar energy reaching it.[164]

text: However, examination of Archaean sediments appears inconsistent with the hypothesis of high greenhouse concentrations. Instead, the moderate temperature range may be explained by a lower surface albedo brought about by less continental area and the "lack of biologically induced cloud condensation nuclei". This would have led to increased absorption of solar energy, thereby compensating for the lower solar output.[165]

text: History of observation

text: The enormous effect of the Sun on Earth has been recognized since prehistoric times, and the Sun has been regarded by some cultures as a deity.

text: Early understanding

text: The Sun has been an object of veneration in many cultures throughout human history. Humanity's most fundamental understanding of the Sun is as the luminous disk in the sky, whose presence above the horizon creates day and whose absence causes night. In many prehistoric and ancient cultures, the Sun was thought to be a solar deity or other supernatural entity. Worship of the Sun was central to civilizations such as the ancient Egyptians, the Inca of South America and the Aztecs of what is now Mexico. In religions such as Hinduism, the Sun is still considered a god. Many ancient monuments were constructed with solar phenomena in mind; for example, stone megaliths accurately mark the summer or winter solstice (some of the most prominent megaliths are located in Nabta Playa, Egypt; Mnajdra, Malta and at Stonehenge, England); Newgrange, a prehistoric human-built mount in Ireland, was designed to detect the winter solstice; the pyramid of El Castillo at Chichén Itzá in Mexico is designed to cast shadows in the shape of serpents climbing the pyramid at the vernal and autumnal equinoxes.

text: The Egyptians portrayed the god Ra as being carried across the sky in a solar barque, accompanied by lesser gods, and to the Greeks, he was Helios, carried by a chariot drawn by fiery horses. From the reign of Elagabalus in the late Roman Empire the Sun's birthday was a holiday celebrated as Sol Invictus (literally "Unconquered Sun") soon after the winter solstice, which may have been an antecedent to Christmas. Regarding the fixed stars, the Sun appears from Earth to revolve once a year along the ecliptic through the zodiac, and so Greek astronomers categorized it as one of the seven planets (Greek planetes, "wanderer"); the naming of the days of the weeks after the seven planets dates to the Roman era.[166][167][168]

text: Development of scientific understanding

text: In the early first millennium BC, Babylonian astronomers observed that the Sun's motion along the ecliptic is not uniform, though they did not know why; it is today known that this is due to the movement of Earth in an elliptic orbit around the Sun, with Earth moving faster when it is nearer to the Sun at perihelion and moving slower when it is farther away at aphelion.[169]

text: One of the first people to offer a scientific or philosophical explanation for the Sun was the Greek philosopher Anaxagoras. He reasoned that it was not the chariot of Helios, but instead a giant flaming ball of metal even larger than the land of the Peloponnesus and that the Moon reflected the light of the Sun.[170] For teaching this heresy, he was imprisoned by the authorities and sentenced to death, though he was later released through the intervention of Pericles. Eratosthenes estimated the distance between Earth and the Sun in the 3rd century BC as "of stadia myriads 400 and 80000", the translation of which is ambiguous, implying either 4,080,000 stadia (755,000 km) or 804,000,000 stadia (148 to 153 million kilometers or 0.99 to 1.02 AU); the latter value is correct to within a few percent. In the 1st century AD, Ptolemy estimated the distance as 1,210 times the radius of Earth, approximately 7.71 million kilometers (0.0515 AU).[171]

text: The theory that the Sun is the center around which the planets orbit was first proposed by the ancient Greek Aristarchus of Samos in the 3rd century BC, and later adopted by Seleucus of Seleucia (see Heliocentrism). This view was developed in a more detailed mathematical model of a heliocentric system in the 16th century by Nicolaus Copernicus.

text: Observations of sunspots were recorded during the Han Dynasty (206 BC–AD 220) by Chinese astronomers, who maintained records of these observations for centuries. Averroes also provided a description of sunspots in the 12th century.[172] The invention of the telescope in the early 17th century permitted detailed observations of sunspots by Thomas Harriot, Galileo Galilei and other astronomers. Galileo posited that sunspots were on the surface of the Sun rather than small objects passing between Earth and the Sun.[173]

text: Arabic astronomical contributions include Albatenius' discovery that the direction of the Sun's apogee (the place in the Sun's orbit against the fixed stars where it seems to be moving slowest) is changing.[174] (In modern heliocentric terms, this is caused by a gradual motion of the aphelion of the Earth's orbit). Ibn Yunus observed more than 10,000 entries for the Sun's position for many years using a large astrolabe.[175]

text: From an observation of a transit of Venus in 1032, the Persian astronomer and polymath Avicenna concluded that Venus is closer to Earth than the Sun.[176] In 1672 Giovanni Cassini and Jean Richer determined the distance to Mars and were thereby able to calculate the distance to the Sun.

text: In 1666, Isaac Newton observed the Sun's light using a prism, and showed that it is made up of light of many colors.[177] In 1800, William Herschel discovered infrared radiation beyond the red part of the solar spectrum.[178] The 19th century saw advancement in spectroscopic studies of the Sun; Joseph von Fraunhofer recorded more than 600 absorption lines in the spectrum, the strongest of which are still often referred to as Fraunhofer lines. In the early years of the modern scientific era, the source of the Sun's energy was a significant puzzle. Lord Kelvin suggested that the Sun is a gradually cooling liquid body that is radiating an internal store of heat.[179] Kelvin and Hermann von Helmholtz then proposed a gravitational contraction mechanism to explain the energy output, but the resulting age estimate was only 20 million years, well short of the time span of at least 300 million years suggested by some geological discoveries of that time.[179][180] In 1890 Joseph Lockyer, who discovered helium in the solar spectrum, proposed a meteoritic hypothesis for the formation and evolution of the Sun.[181]

text: Not until 1904 was a documented solution offered. Ernest Rutherford suggested that the Sun's output could be maintained by an internal source of heat, and suggested radioactive decay as the source.[182] However, it would be Albert Einstein who would provide the essential clue to the source of the Sun's energy output with his mass-energy equivalence relation E = mc2.[183] In 1920, Sir Arthur Eddington proposed that the pressures and temperatures at the core of the Sun could produce a nuclear fusion reaction that merged hydrogen (protons) into helium nuclei, resulting in a production of energy from the net change in mass.[184] The preponderance of hydrogen in the Sun was confirmed in 1925 by Cecilia Payne using the ionization theory developed by Meghnad Saha, an Indian physicist. The theoretical concept of fusion was developed in the 1930s by the astrophysicists Subrahmanyan Chandrasekhar and Hans Bethe. Hans Bethe calculated the details of the two main energy-producing nuclear reactions that power the Sun.[185][186] In 1957, Margaret Burbidge, Geoffrey Burbidge, William Fowler and Fred Hoyle showed that most of the elements in the universe have been synthesized by nuclear reactions inside stars, some like the Sun.[187]

text: Solar space missions

text: The first satellites designed to observe the Sun were NASA's Pioneers 5, 6, 7, 8 and 9, which were launched between 1959 and 1968. These probes orbited the Sun at a distance similar to that of Earth, and made the first detailed measurements of the solar wind and the solar magnetic field. Pioneer 9 operated for a particularly long time, transmitting data until May 1983.[189][190]

text: In the 1970s, two Helios spacecraft and the Skylab Apollo Telescope Mount provided scientists with significant new data on solar wind and the solar corona. The Helios 1 and 2 probes were U.S.–German collaborations that studied the solar wind from an orbit carrying the spacecraft inside Mercury's orbit at perihelion.[191] The Skylab space station, launched by NASA in 1973, included a solar observatory module called the Apollo Telescope Mount that was operated by astronauts resident on the station.[102] Skylab made the first time-resolved observations of the solar transition region and of ultraviolet emissions from the solar corona.[102] Discoveries included the first observations of coronal mass ejections, then called "coronal transients", and of coronal holes, now known to be intimately associated with the solar wind.[191]

text: In 1980, the Solar Maximum Mission was launched by NASA. This spacecraft was designed to observe gamma rays, X-rays and UV radiation from solar flares during a time of high solar activity and solar luminosity. Just a few months after launch, however, an electronics failure caused the probe to go into standby mode, and it spent the next three years in this inactive state. In 1984 Space Shuttle Challenger mission STS-41C retrieved the satellite and repaired its electronics before re-releasing it into orbit. The Solar Maximum Mission subsequently acquired thousands of images of the solar corona before re-entering Earth's atmosphere in June 1989.[192]

text: Launched in 1991, Japan's Yohkoh (Sunbeam) satellite observed solar flares at X-ray wavelengths. Mission data allowed scientists to identify several different types of flares, and demonstrated that the corona away from regions of peak activity was much more dynamic and active than had previously been supposed. Yohkoh observed an entire solar cycle but went into standby mode when an annular eclipse in 2001 caused it to lose its lock on the Sun. It was destroyed by atmospheric re-entry in 2005.[193]

text: One of the most important solar missions to date has been the Solar and Heliospheric Observatory, jointly built by the European Space Agency and NASA and launched on 2 December 1995.[102] Originally intended to serve a two-year mission, a mission extension through 2012 was approved in October 2009.[194] It has proven so useful that a follow-on mission, the Solar Dynamics Observatory (SDO), was launched in February 2010.[195] Situated at the Lagrangian point between Earth and the Sun (at which the gravitational pull from both is equal), SOHO has provided a constant view of the Sun at many wavelengths since its launch.[102] Besides its direct solar observation, SOHO has enabled the discovery of a large number of comets, mostly tiny sungrazing comets that incinerate as they pass the Sun.[196]

text: All these satellites have observed the Sun from the plane of the ecliptic, and so have only observed its equatorial regions in detail. The Ulysses probe was launched in 1990 to study the Sun's polar regions. It first travelled to Jupiter, to "slingshot" into an orbit that would take it far above the plane of the ecliptic. Once Ulysses was in its scheduled orbit, it began observing the solar wind and magnetic field strength at high solar latitudes, finding that the solar wind from high latitudes was moving at about 750 km/s, which was slower than expected, and that there were large magnetic waves emerging from high latitudes that scattered galactic cosmic rays.[197]

text: Elemental abundances in the photosphere are well known from spectroscopic studies, but the composition of the interior of the Sun is more poorly understood. A solar wind sample return mission, Genesis, was designed to allow astronomers to directly measure the composition of solar material.[198]

text: The Solar Terrestrial Relations Observatory (STEREO) mission was launched in October 2006. Two identical spacecraft were launched into orbits that cause them to (respectively) pull further ahead of and fall gradually behind Earth. This enables stereoscopic imaging of the Sun and solar phenomena, such as coronal mass ejections.[199][200]

text: The Indian Space Research Organisation has scheduled the launch of a 100 kg satellite named Aditya for 2017–18. Its main instrument will be a coronagraph for studying the dynamics of the Solar corona.[201]

text: Observation and effects

text: The brightness of the Sun can cause pain from looking at it with the naked eye; however, doing so for brief periods is not hazardous for normal non-dilated eyes.[202][203] Looking directly at the Sun causes phosphene visual artifacts and temporary partial blindness. It also delivers about 4 milliwatts of sunlight to the retina, slightly heating it and potentially causing damage in eyes that cannot respond properly to the brightness.[204][205] UV exposure gradually yellows the lens of the eye over a period of years, and is thought to contribute to the formation of cataracts, but this depends on general exposure to solar UV, and not whether one looks directly at the Sun.[206] Long-duration viewing of the direct Sun with the naked eye can begin to cause UV-induced, sunburn-like lesions on the retina after about 100 seconds, particularly under conditions where the UV light from the Sun is intense and well focused;[207][208] conditions are worsened by young eyes or new lens implants (which admit more UV than aging natural eyes), Sun angles near the zenith, and observing locations at high altitude.

text: Viewing the Sun through light-concentrating optics such as binoculars may result in permanent damage to the retina without an appropriate filter that blocks UV and substantially dims the sunlight. When using an attenuating filter to view the Sun, the viewer is cautioned to use a filter specifically designed for that use. Some improvised filters that pass UV or IR rays, can actually harm the eye at high brightness levels.[209] Herschel wedges, also called Solar Diagonals, are effective and inexpensive for small telescopes. The sunlight that is destined for the eyepiece is reflected from an unsilvered surface of a piece of glass. Only a very small fraction of the incident light is reflected. The rest passes through the glass and leaves the instrument. If the glass breaks because of the heat, no light at all is reflected, making the device fail-safe. Simple filters made of darkened glass allow the full intensity of sunlight to pass through if they break, endangering the observer's eyesight. Unfiltered binoculars can deliver hundreds of times as much energy as using the naked eye, possibly causing immediate damage. It is claimed that even brief glances at the midday Sun through an unfiltered telescope can cause permanent damage.[210]

text: Partial solar eclipses are hazardous to view because the eye's pupil is not adapted to the unusually high visual contrast: the pupil dilates according to the total amount of light in the field of view, not by the brightest object in the field. During partial eclipses most sunlight is blocked by the Moon passing in front of the Sun, but the uncovered parts of the photosphere have the same surface brightness as during a normal day. In the overall gloom, the pupil expands from ~2 mm to ~6 mm, and each retinal cell exposed to the solar image receives up to ten times more light than it would looking at the non-eclipsed Sun. This can damage or kill those cells, resulting in small permanent blind spots for the viewer.[211] The hazard is insidious for inexperienced observers and for children, because there is no perception of pain: it is not immediately obvious that one's vision is being destroyed.

text: During sunrise and sunset, sunlight is attenuated because of Rayleigh scattering and Mie scattering from a particularly long passage through Earth's atmosphere,[212] and the Sun is sometimes faint enough to be viewed comfortably with the naked eye or safely with optics (provided there is no risk of bright sunlight suddenly appearing through a break between clouds). Hazy conditions, atmospheric dust, and high humidity contribute to this atmospheric attenuation.[213]

text: An optical phenomenon, known as a green flash, can sometimes be seen shortly after sunset or before sunrise. The flash is caused by light from the Sun just below the horizon being bent (usually through a temperature inversion) towards the observer. Light of shorter wavelengths (violet, blue, green) is bent more than that of longer wavelengths (yellow, orange, red) but the violet and blue light is scattered more, leaving light that is perceived as green.[214]

text: Ultraviolet light from the Sun has antiseptic properties and can be used to sanitize tools and water. It also causes sunburn, and has other biological effects such as the production of vitamin D and sun tanning. Ultraviolet light is strongly attenuated by Earth's ozone layer, so that the amount of UV varies greatly with latitude and has been partially responsible for many biological adaptations, including variations in human skin color in different regions of the globe.[215]

text: Planetary system

text: The Sun has eight known planets. This includes four terrestrial planets (Mercury, Venus, Earth, and Mars), two gas giants (Jupiter and Saturn), and two ice giants (Uranus and Neptune). The Solar System also has at least five dwarf planets, an asteroid belt, numerous comets, and a large number of icy bodies which lie beyond the orbit of Neptune.