The galactic year, also known as a cosmic year, is the duration of time required for the Sun to orbit once around the center of the Milky Way Galaxy. Estimates of the duration of one orbit range from 225 to 250 million terrestrial years. The Solar System is traveling at an average speed of 230 km/s (828,000 km/h) or 143 mi/s (514,000 mph) within its trajectory around the galactic center, a speed at which an object could circumnavigate the Earth's equator in 2 minutes and 54 seconds; that speed corresponds to approximately 1/1300 of the speed of light.
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.
The following list assumes that 1 galactic year is 225 million years.
|About 61.32 galactic years ago||Big Bang|
|About 54 galactic years ago||Birth of the Milky Way|
|20.44 galactic years ago||Birth of the Sun|
|17–18 galactic years ago||Oceans appear on Earth|
|16.889 galactic years ago||Life begins on Earth|
|15.555 galactic years ago||Prokaryotes appear|
|12 galactic years ago||Bacteria appear|
|10 galactic years ago||Stable continents appear|
|6.8 galactic years ago||Multicellular organisms appear|
|6.666 galactic years ago||Eukaryotes appear|
|2.4 galactic years ago||Cambrian explosion occurs|
|2 galactic years ago||The first brain structure appears in worms|
|1.11 galactic year ago||Permian–Triassic extinction event|
|0.2935 galactic years ago||Cretaceous–Paleogene extinction event|
|0.15 galactic year from now||Mean time between impacts of asteroidal bodies in the order of magnitude of the K/Pg impactor has elapsed.|
|1 galactic year from now||All the continents on Earth may fuse into a supercontinent. Three potential arrangements of this configuration have been dubbed Amasia, Novopangaea, and Pangaea Ultima.|
|2–3 galactic years from now||Tidal acceleration moves the Moon far enough from Earth that total solar eclipses are no longer possible|
|4 galactic years from now||Carbon dioxide levels fall to the point at which C4 photosynthesis is no longer possible. Multicellular life dies out|
|15 galactic years from now||Surface conditions on Earth are comparable to those on Venus today|
|22 galactic years from now||The Milky Way and Andromeda Galaxy begin to collide|
|25 galactic years from now||Sun ejects a planetary nebula, leaving behind a white dwarf|
|30 galactic years from now||The Milky Way and Andromeda complete their merger into a giant elliptical galaxy called Milkomeda or Milkdromeda |
|500 galactic years from now||The Universe's expansion causes all galaxies beyond the Milky Way's Local Group to disappear beyond the cosmic light horizon, removing them from the observable universe |
|2000 galactic years from now||Local Group of 47 galaxies coalesces into a single large galaxy |
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.