The Sun is moving with the Milky Way
The Sun is not parked while the galaxy turns around it. It travels through the Milky Way along with its planets, pulled inward by the gravity of the galaxy’s stars, gas, and dark matter. The orbit is broadly around the galactic center, but it is not a rigid circular track: the Sun also bobs above and below the galaxy’s flattened disk as it goes.
That distinction matters because the Milky Way is not a solid wheel. Its spiral arms are regions where stars and gas gather more densely, not fixed spokes that every star follows. The Sun’s route is shaped by the gravity of the galaxy as a whole, rather than by a single object at its center. The central black hole, though enormous, is only a small part of the mass governing the Sun’s galactic orbit.
A clock for the galaxy, not for life on Earth
A “galactic year” is a convenient name for one full circuit of the Sun around the Milky Way’s center. It gives astronomers a way to describe the Sun’s motion on a scale far larger than the familiar orbit of Earth around the Sun. The two years measure different journeys: one is a planetary lap, the other a stellar one.
The timescale also makes Earth’s history look different. The non-avian dinosaurs disappeared about 66 million years ago—less than one-third of a galactic year. So when the Sun completes its next circuit, the stars and planets will have made a vast journey, but life on Earth will have experienced only a small slice of it.
