<P> 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 length of one orbit range from 225 to 250 million terrestrial years . The Solar System is traveling at an average speed of 828,000 km / h (230 km / s) or 514,000 mph (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 one 1300th of the speed of light . </P> <P> 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 . </P>

How long for sun to rotate around galaxy