Astrophysics (Index)About

gigayear

(Gy, Gyr, eon, aeon)
(a billion years)

A gigayear, a billion years, is a common unit for cosmological times and time intervals, convenient, given that the current age-determination of the universe is between 13 and 14 gigayears. Abbreviations include Gy and Gyr. The word eon (or aeon) has sometimes been used within astronomy to indicate a gigayear, but is more widely used to mean "a very long time", and in geology it is used for specific periods within the geological timeline. A gigayear is on the order of 1016 seconds, more specifically 3.15576 × 1016.

Given the finite speed of light (c), when we observe something at some number of billions of light-years' distant, we are observing it that many gigayears in its past.

The term giga-anum (Gya) is used specifically for a billion years in the past, i.e., counting backward from now.


(unit,time)
Further reading:
https://en.wikipedia.org/wiki/Billion_years
https://en.wikipedia.org/wiki/Aeon
https://en.wiktionary.org/wiki/gigayear
http://astronomy.nmsu.edu/geas/lectures/lecture02/slide04.html

Referenced by pages:
47 Tucanae (47 Tuc)
alpha-enhanced
astronomical quantities
black hole merger
celestial reference frame
cosmological redshift
cosmological simulation
Gaia Enceladus
galaxy merger
GW170817
Hubble time (tH)
Lyapunov time
Messier 15 (M15)
Messier 67 (M67)
Milkomeda
neutron star merger
NGC 3201
nova (N)
observable universe
quenched galaxy
[α/Fe] versus [Fe/H] diagram

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