Galactic year

Approximate orbit of the Sun (yellow circle) around the Galactic Center

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.^[1] One galactic year is approximately 225 million Earth years.^[2] 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,^[3] 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.^[4]

^ Cosmic Year Archived 2014-04-12 at the Wayback Machine, 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

[akb-1] Cosmic Year Archived 2014-04-12 at the Wayback Machine, Fact Guru, University of Ottawa

[biblio-2] Leong, Stacy (2002). "Period of the Sun's Orbit around the Galaxy (Cosmic Year)". The Physics Factbook.

[StarChild-3] ttp://starchild.gsfc.nasa.gov/docs/StarChild/questions/question18.html NASA – StarChild Question of the Month for February 2000

[timeline-4] Geologic Time Scale – as 18 galactic rotations

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