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''Pale Blue Dot'' is a photograph of planet Earth taken on February 14, 1990, by the ''Voyager 1'' space probe from a record distance of about kilometers ( miles, 40.5 AU), as part of the ''Family Portrait'' series of images of the Solar System. In the photograph, Earth's apparent size is less than a pixel; the planet appears as a tiny dot against the vastness of space, among bands of sunlight scattered by the camera's optics.〔(【引用サイトリンク】title=A Pale Blue Dot )〕 ''Voyager 1'', which had completed its primary mission and was leaving the Solar System, was commanded by NASA to turn its camera around and take one last photograph of Earth across a great expanse of space, at the request of astronomer and author Carl Sagan.〔(【引用サイトリンク】title=From Earth to the Solar System, The Pale Blue Dot )〕 == Background == On September 5, 1977, NASA launched ''Voyager 1'', a robotic spacecraft on a mission to study the outer Solar System and eventually interstellar space.〔(【引用サイトリンク】title=Mission Overview )〕〔(【引用サイトリンク】title=Voyager 1 )〕 After encountering the Jovian system in 1979 and the Saturnian system in 1980, the primary mission was declared complete on November 20 of the same year. ''Voyager 1'' was the first space probe to provide detailed images of the two largest planets and their major moons. The spacecraft, travelling at , is the farthest man-made object from Earth and the first one to leave the Solar System.〔 Its mission has been extended and continues to this day, with the aim of investigating the boundaries of the Solar system, including the Kuiper belt, the heliosphere and interstellar space. Operating for as of today (), it receives routine commands and transmits data back to the Deep Space Network.〔〔(【引用サイトリンク】title=An Earthly View of Mars )〕 ''Voyager 1'' was initially expected to work only through the Saturn encounter. When the spacecraft passed the planet in 1980, Sagan proposed the idea of the space probe taking one last picture of Earth.〔(【引用サイトリンク】title=It's our dot : For Carl Sagan, planet Earth is just a launch pad for human explorations of the outer universe )〕 He pointed out that such a picture would not have had much scientific value, as the Earth would appear too small for ''Voyager''s cameras to make out any detail, but it could have been meaningful nevertheless as a perspective on our place in the universe. Although many in NASA's Voyager program were supportive, most were of the opinion that taking a picture of Earth close to the Sun risked damaging the spacecraft's video system, preventing more pictures from being taken.〔(【引用サイトリンク】title=Voyager Celebrates 20-Year-Old Valentine to Solar System )〕 It was not until 1989 that Sagan's idea was put into practice, but then instrument calibrations delayed the process further, and the personnel who devised and transmitted the radio commands to ''Voyager 1'' were also being laid off or transferred to other projects. Finally, NASA Administrator Richard Truly interceded to ensure that the photograph was taken.〔Sagan, 1994, (pp. 4–5 )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「pale blue dot」の詳細全文を読む スポンサード リンク
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