What is Galactic year? Definition, Meaning & Explanation

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Our planet completes one cycle around the Milky Way galaxy in 23 million years, so we are in our 20th galactic year.

A galactic year is the period of time in which our Sun completes one cycle around the center of the galaxy. As our planet i.e. the Earth revolves around the Sun, so we can say that the Earth also revolves around the center of the galaxy. The Solar System is traveling (orbiting) around the center of the Milky Way Galaxy at an average speed of 230 kilometers per second (142 miles per second). At this speed, a body can orbit the Earth's equator in about 2 minutes and 54 seconds. A galactic year is equal to 23 million Earth years. The galactic year provides an easy-to-use equation for representing cosmological and geologic time intervals together.

The Milky Way galaxy is about 0.1 million light-years in diameter, and the Sun is about 28,000 light-years away from the center of the Milky Way galaxy. If we measure the history of the universe in galactic years, then the age of the Earth will be only 16 years, while the age of the sun will be 20 years and the age of the universe will be equal to 60 years. It means that according to all recorded human history to date, our Earth has barely completed one cycle. Other celestial bodies have different intervals of galactic years depending on how close they are to the center of the Milky Way galaxy.

Celestial bodies that are closer to the center of the galaxy complete more cycles than those that are further away from the center. In other words, the bodies that are located near the center of the Milky Way galaxy have shorter galactic years. But the galaxy itself is not in a stationary state. It is moving due to gravitational attraction. This means that the Earth is orbiting the Sun, the Sun is orbiting the Milky Way, and the Milky Way Galaxy is moving toward the Andromeda Galaxy.