Since the sun is about 26,000 light-years from the centre of the milky way the sun travels at a speed of about 782,000 km per hour in a circular orbit around the centre of the milky way.
As sun itself is formed some 4.6 billion years ago the sun thus needs to speed up and this phenomenon is called as the cosmic year i.e is the amount of the time it will take the sun to reach the centre of the galaxy.