Byr
1559376
218979411
2008-06-13T01:10:19Z
Kevin Murray
1032142
no consensus to merge
'''Byr''' was formerly used in [[English-language]] [[geology]] and [[astronomy]] as a [[physical unit|unit]] of one [[1,000,000,000 (number)|billion]] [[year]]s. The "B" is an abbreviation for "billion" (meaning thousand million), with "yr" simply an abbreviation for "year". Today, the term [[gigaannum]] (Ga) is also used, but Gy or Gyr are still sometimes used in English-language works (at the risk of confusion with the [[gray (unit)|gray]]).
Because a [[Long and short scales|billion]] means 1000 million in some countries but can mean a million million in others its use is deprecated in favour of [[giga-]] which unambiguously means 10<sup>9</sup> and [[annum]] which for precision may be qualified by ([[sidereal]]), ([[Julian calendar|Julian]]), etc.
==See also==
*[[gigaannum]]
*[[Myr]]
[[Category:Units of time]]
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