The galactic year, also known as a cosmic year, is the duration of time required for the
Sun to
orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...
once around the
center of the
Milky Way Galaxy.
[Cosmic Year](_blank)
, Fact Guru, University of Ottawa One galactic year is 230 million
Earth 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,
[http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question18.html NASA – StarChild Question of the Month for February 2000] 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.
[Geologic Time Scale – as 18 galactic rotations](_blank)
/ref>
Timeline of the universe and Earth's history in galactic years
The following list assumes that 1 galactic year is 225 million years.
See also
* Galactic Tick Day
* Geologic time scale
The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochr ...
References
{{DEFAULTSORT:Galactic Year
Milky Way
Types of year