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A gigaannum or gigayear (Byr, Gyr or Gy) is a period of one billion years (109 or 1,000,000,000 years). Retrospect time periods may be expressed as X billion years ago (bya). The prefix giga- is preferred to billion- to avoid confusion in the long and short scales over the meaning of billion; the postfix annum may be further qualified for precision as a sidereal year or Julian year. Byr was formerly used in English-language geology and astronomy as a unit of one billion years. Subsequently the term gigaannum (Ga) has increased in usage, with Gy or Gyr still sometimes used in English-language works, at the risk of confusion with the gray). Astronomers use Gyr or Gy as an abbreviation for gigayear. ==See also== * Myr * Year * Before Present * Gigaannum or Ga * Gya * mya (unit) * Orders of magnitude (time)#Years * Symbols y and yr 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「A gigaannum or gigayear (Byr, Gyr or Gy) is a period of one billion years (109 or 1,000,000,000 years). Retrospect time periods may be expressed as X billion years ago (bya). The prefix giga- is preferred to billion- to avoid confusion in the long and short scales over the meaning of billion; the postfix annum may be further qualified for precision as a sidereal year or Julian year.Byr was formerly used in English-language geology and astronomy as a unit of one billion years. Subsequently the term gigaannum (Ga) has increased in usage, with Gy or Gyr still sometimes used in English-language works, at the risk of confusion with the gray). Astronomers use Gyr or Gy as an abbreviation for gigayear.==See also==* Myr* Year* Before Present* Gigaannum or Ga* Gya* mya (unit)* Orders of magnitude (time)」の詳細全文を読む スポンサード リンク
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