Galactic year

The galactic year, also known as a cosmic year, is the length of time needed for the Sun to orbit once around the center of the Milky Way Galaxy.^[1] One galactic year is 230 million Earth years.^[2] The Solar System is traveling at an average speed of 230 km/s (828,000 km/h) within its arc-like path around the galactic center,^[3] a speed at which an object could travel around the Earth's equator in 2 minutes and 54 seconds; that speed goes along with about 1/1300 of the speed of light.

The galactic year provides a conveniently usable unit for showing cosmic and geological time periods together. Very differently, a "billion-year" scale does not allow for useful difference between geologic events, and a "million-year" scale needs some rather large numbers.^[4]

1. ↑ Cosmic Year Archived 2014-04-12 at the Wayback Machine, Fact Guru, University of Ottawa
2. ↑ Leong, Stacy (2002). "Period of the Sun's Orbit around the Galaxy (Cosmic Year)". The Physics Factbook.
3. ↑ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question18.html NASA – StarChild Question of the Month for February 2000
4. ↑ Geologic Time Scale – as 18 galactic rotations