Galactic year
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 Solar System is traveling at an average speed of 828,000 km/h (230 km/s) or 514,000 mph (143 mi/s) within its trajectory around the galactic center,[3] which is about one 1300th of the speed of light—a speed at which an object could circumnavigate the Earth's equator in 2 minutes and 54 seconds.
The galactic year provides a conveniently usable unit for depicting cosmic and geological time periods together. 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.[4]
Timeline of universe's and earth's history in galactic years
The following list assumes that 1 galactic year is 225 million years.
about 61 galactic years ago | Big Bang |
about 54 galactic years ago | Birth of the Milky Way |
18.4 galactic years ago | Birth of the Sun |
17-18 galactic years ago | Oceans appear on Earth |
15 galactic years ago | Life begins on Earth |
14 galactic years ago | Prokaryotes appear |
13 galactic years ago | Bacteria appear |
10 galactic years ago | Stable continents appear |
7 galactic years ago | Eukaryotes appear |
6.8 galactic years ago | Multicellular organisms appear |
2.8 galactic years ago | Cambrian explosion |
1 galactic year ago | Permian–Triassic extinction event |
0.26 galactic years ago | Cretaceous–Paleogene extinction event |
0.001 galactic years ago | Appearance of modern humans |
Present day | |
---|---|
22 galactic years in the future | The Milky Way and Andromeda Galaxy begin to collide |
25 galactic years in the future | Sun ejects a planetary nebula, leaving behind a white dwarf |
See also
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://starchild.gsfc.nasa.gov/docs/StarChild/questions/question18.html NASA - StarChild Question of the Month for February 2000
- ^ Geologic Time Scale - as 18 galactic rotations
- ^ "Milky Way Past Was More Turbulent Than Previously Known". ESO News. European Southern Observatory. 2004-04-06.
After more than 1,000 nights of observations spread over 15 years, they have determined the spatial motions of more than 14,000 solar-like stars residing in the neighbourhood of the Sun.