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 (also known as orbital revolution) 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 ...
once around the
center of the
Milky Way Galaxy.
[Cosmic Year](_blank)
, Fact Guru, University of Ottawa
The University of Ottawa (), often referred to as uOttawa or U of O, is a Official bilingualism in Canada, bilingual public research university in Ottawa, Ontario, Canada. The main campus is located on directly to the northeast of Downtown Ot ...
One galactic year is approximately 225 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 geochro ...
References
{{DEFAULTSORT:Galactic Year
Milky Way
Types of year