The idea that the Sun is a fixed anchor at the heart of our solar system is inaccurate. Our star is far from stationary, engaging in a complex, high-speed journey through the cosmos. The Sun orbits on two distinct scales: locally, influenced by the planets, and massively, around the center of the Milky Way galaxy.
The Sun’s Galactic Orbit
The Sun’s primary movement is its grand orbit around the Galactic Center of the Milky Way. This structure is anchored by the supermassive black hole, Sagittarius A, which serves as the gravitational focal point for the entire galaxy. The Sun resides about 27,000 light-years away within one of the galaxy’s spiral arms.
Our solar system is situated in a minor spiral feature of the galaxy called the Orion Spur. As the Sun circles the galaxy, it brings the entire solar system—including planets, asteroids, and comets—along with it. This motion is not a perfect, flat circle, but follows a complex, oscillating path.
The Sun also bobs vertically through the flat plane of the Milky Way’s disk. This vertical movement causes it to move above and below the mid-plane of the galaxy. This complex, roughly elliptical path is influenced by the non-uniform distribution of mass throughout the galaxy.
Understanding the Solar System’s Barycenter
The Sun’s motion is also influenced on a local scale by the gravitational pull of its planets. In any system of orbiting bodies, the objects revolve around a common center of mass, known as the barycenter. This point is a balance point determined by the masses of the celestial bodies and their relative distances.
Since the Sun holds over 99.8% of the solar system’s total mass, the barycenter is usually very close to its center. However, the mass of the giant planets, particularly Jupiter, is substantial enough to shift this balance point. When the giant planets align, their combined gravitational pull can move the solar system’s barycenter outside the physical surface of the Sun.
The Sun is not perfectly stationary, but instead orbits this constantly shifting barycenter. This movement causes the Sun to appear to “wobble” through space as the giant planets move through their orbits. Calculations suggest the solar system’s barycenter spends approximately 62% of the time outside the Sun’s physical boundary.
Measuring the Speed and Trajectory of the Sun
The scale of the Sun’s galactic movement is vast and involves impressive speeds. The Sun travels around the Galactic Center at an estimated average velocity of 220 to 230 kilometers per second. This speed converts to about 490,000 to 514,000 miles per hour, carrying the entire solar system.
Despite this immense velocity, the sheer size of the Milky Way means the Sun takes a long time to complete a single circuit. One full orbit around the Galactic Center is known as a galactic year, which takes roughly 225 to 230 million Earth years. Since its formation, the Sun has completed about 20 to 25 of these galactic orbits.
The vertical bobbing motion through the galactic disk is an important aspect of the Sun’s trajectory. The period for this up-and-down oscillation is estimated to be about 60 million years. This complex, three-dimensional motion ensures the Sun is constantly moving, both locally around the barycenter and massively through the galaxy.