Galactic year


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 or 143 mi/s 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..

Timeline of the universe and Earth's history in galactic years

The following list assumes that 1 galactic year is 225 million years.