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Exa is a decimal unit prefix in the metric system denoting 1018 or . It was added as an SI prefix to the International System of Units (SI) in 1975,〔(【引用サイトリンク】title=Resolution 10 of the 15th meeting of the CGPM (1975) )〕 and has the unit symbol E. ''Exa'' comes from the Ancient Greek , used as a prefix , meaning ''six'' (like hexa-), because it is equal to 10006. Examples: * The total storage needed by Google Mail as of April 2012, ignoring backups and compression, is more than an exabyte (10,240 megabytes of storage per user multiplied by an estimated 260 million users). * 1 EeV = 1018 electronvolts = 0.1602 joule * 1 exasecond is approximately 32 billion years * 1 exametre is approximately 110 light years * 0.43 Es ≈ the approximate age of the Universe * 1.6 Em—172 ± 12.5 light years—Diameter of Omega Centauri (one of the largest known globular clusters, perhaps containing over a million stars)〔distance × sin( diameter_angle ), using distance of 5 kpc (15.8 ± 1.1 kly) and angle 36.3', = 172 ± 12.5 ly.〕 ==See also== * 1 exametre * Exabyte * Exasecond * Orders of magnitude (numbers) * Metric prefix * Binary prefix 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「Exa-」の詳細全文を読む スポンサード リンク
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