Galactic year Information & Galactic year Links at HealthHaven.com

Panoramic image of the Milky Way, taken from Death Valley.

The galactic year, also known as a cosmic year, is the duration of time required for the solar system to orbit once around the center of the Milky Way galaxy.^[1] Estimates of the length of one orbit range from 225 to 250 million "terrestrial" years. ^[2]

The galactic year provides a conveniently "graspable" unit for thinking about cosmic and geological time periods. (By contrast, a "billion-year" scale does not allow for useful discrimination between geologic events, and a "million-year" scale requires some rather large numbers.) ^[3]

[edit] Timeline of earth's history in galactic years

In this list, 1 galactic year (GY) = 225 million years

0 GY: Birth of the Sun
4 GY: Oceans appear on Earth
5 GY: Life begins
6 GY: Prokaryotes appear
7 GY: Bacteria appear
10 GY: Stable continents appear
13 GY: Eukaryotes appear
16 GY: Multicellular organisms appear
17.8 GY: Cambrian explosion
19 GY: Great Dying
19.6 GY: K–T extinction event
19.999 GY: Appearance of modern humans
20 GY: Present day

[edit] See also

Astronomy portal

List of unusual units of measurement

[edit] References

^ Cosmic Year, Fact Guru, University of Ottawa
^ Leong, Stacy (2002). "Period of the Sun's Orbit around the Galaxy (Cosmic Year)". The Physics Factbook. http://hypertextbook.com/facts/2002/StacyLeong.shtml.
^ Geologic Time Scale - as 18 galactic rotations

[akb-0] Cosmic Year, Fact Guru, University of Ottawa

[biblio-1] Leong, Stacy (2002). "Period of the Sun's Orbit around the Galaxy (Cosmic Year)". The Physics Factbook. http://hypertextbook.com/facts/2002/StacyLeong.shtml.

[timeline-2] Geologic Time Scale - as 18 galactic rotations

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