A galactic year, also known as a cosmic year or galactic period, is the length of time it takes for the Sun to complete one orbit around the center of the Milky Way galaxy. The Milky Way is a barred spiral galaxy, and the Sun is located about 25,000 light-years from the galactic center in one of the spiral arms.
The exact duration of a galactic year is difficult to determine precisely because the Sun’s orbit is affected by gravitational forces from other stars and structures in the galaxy. However, estimates place the length of a galactic year at around 225 million Earth years. To put it simply, by the time our Sun completes one round of the Milky-way, the Earth has completed 225 million orbits of the Sun.
The concept of a galactic year is useful for studying the long-term evolution of the Milky Way galaxy and its stars. By observing the properties and motions of stars and gas in different regions of the galaxy, astronomers can infer information about the structure, and history of the Milky Way over very long timescales.
The Sun’s speed varies depending on what it is being measured relative to. Relative to the center of the Milky Way, our Sun orbits around the center of the Milky Way galaxy at a speed of around 220 kilometers per second, or about 792,000 km per hour. This motion takes the Sun about 225 million Earth years to complete one orbit around the galaxy, which is known as a galactic year. In this period of 225 million years, the sun travels 1.5 into 10 followed by 17 zeros kilometers.