The Solar System is definitively moving through the galaxy, and its motion is far more complex than the simple rotation of a planet around a star. Our system, which includes the Sun, planets, and all orbiting bodies, is in constant, dynamic motion on multiple scales. This movement involves circling the center of the Milky Way, a subtle wave-like oscillation, and a much larger journey with our entire galaxy through the universe. Understanding this cosmic trajectory requires considering the massive gravitational forces at play across vast distances.
The Sun’s Galactic Orbit
The primary movement of the Solar System is its orbit around the gravitational center of the Milky Way galaxy, located approximately 26,000 to 27,000 light-years away. We are currently located within the Orion Arm, one of the galaxy’s minor spiral structures. The Sun travels at a speed of about 220 to 230 kilometers per second (490,000 to 514,000 miles per hour) as it circles the galactic core.
Despite this high velocity, the Solar System requires a vast amount of time to complete a single revolution, a period known as the cosmic year. One full orbit takes approximately 225 to 230 million Earth years. Since the Sun formed about 4.6 billion years ago, it has completed roughly 20 orbits around the galactic center.
The Sun’s path is not a smooth circle, but a complex trajectory that involves a vertical oscillation. As the Solar System moves around the galaxy, it periodically bobs up and down, crossing the thin galactic plane. This wave-like motion is caused by the gravitational pull of the dense matter concentrated in the galactic disk. The Solar System crosses the mid-plane of the galaxy roughly every 30 to 35 million years.
Measuring Our Trajectory
To precisely quantify the Solar System’s motion, astronomers use the Local Standard of Rest (LSR). The LSR is a theoretical reference point that moves in a perfectly circular orbit around the galactic center, representing the average motion of stars in our local neighborhood. The Sun’s velocity relative to the LSR is called its peculiar motion, which is about 18 kilometers per second.
The direction of this peculiar motion is called the Solar Apex, the point in the sky toward which the Sun is heading relative to its nearby stars. This apex is generally located near the star Vega in the constellation Lyra or sometimes cited near the constellation Hercules. This small relative motion is added to the larger 220 km/s orbital speed, resulting in a slightly faster and angled orbit compared to the theoretical LSR.
The total velocity of our Solar System, combining its circular galactic orbit and its peculiar motion, is directed toward the constellation Cygnus. This complexity highlights the difficulty in defining a fixed reference point in space. This combined motion means that the planets never return to the exact same point in space after one revolution around the Sun. Instead, they follow a helical, or spiral, path through the galaxy.
The Motion of the Milky Way
The movement of the Solar System continues beyond its galactic orbit, as the Milky Way itself is also moving through the universe. Our galaxy is a member of the Local Group, a collection that includes the Andromeda galaxy and dozens of smaller systems. This entire group is gravitationally bound and moving together.
The Local Group is being pulled toward the Great Attractor, a much larger concentration of mass located 150 to 250 million light-years away. This region is the central gravitational focus of the Laniakea Supercluster, which contains thousands of galaxies.
To measure the cosmic speed of the Milky Way, astronomers use the Cosmic Microwave Background (CMB) radiation as a universal reference frame. The CMB is the faint afterglow of the Big Bang, and its uniform temperature serves as a baseline for measuring motion. Relative to this background, the Milky Way is traveling at a speed of approximately 600 kilometers per second.