Galactic year


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. Estimates of the length of one orbit range from 225 to 250 million “terrestrial” years. According to NASA, the Solar System is traveling at an average speed of 828,000 km/h (230 km/s) or 514,000 mph (143 mi/s), which is about one 1300th of the speed of light. If you could travel at that speed in a jet aircraft along the equator, you would go all the way around the world in approximately 2 minutes and 54 seconds. According to NASA, even at this incredible speed, it still takes the solar system 230 million years to orbit the center of the Milky Way Galaxy one time.
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.

Timeline of universe’s and earth’s history in galactic years

Assuming 1 galactic year (GY) is approximately 225 million years:
~61 GY ago Big Bang
~54 GY ago Birth of the Milky Way
18.4 GY ago Birth of the Sun
17-18 GY ago Oceans appear on Earth
15 GY ago Life begins on Earth
14 GY ago Prokaryotes appear
13 GY ago Bacteria appear
10 GY ago Stable continents appear
7 GY ago Eukaryotes appear
6.8 GY ago Multicellular organisms appear
2.8 GY ago Cambrian explosion
1 GY ago Permian-Triassic extinction event
0.26 GY ago Cretaceous-Paleogene extinction event
0.001 GY ago Appearance of modern humans
Present day
6 GY in the future Sun’s habitable zone moves outside of the Earth’s orbit
22 GY in the future The Milky Way and Andromeda Galaxy begin to collide
25 GY in the future Sun ejects a planetary nebula, leaving behind a white dwarf

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