From Earth, the Sun appears to traverse the sky, rising and setting daily, and its path changes throughout the year. This observation is a result of Earth’s own motions, not the Sun orbiting our planet. The Sun also undertakes a journey through the Milky Way galaxy, carrying our solar system with it. Understanding these movements illustrates the dynamic nature of our solar system.
The Sun’s Daily Path Across the Sky
The most familiar perceived movement of the Sun is its daily journey from east to west across the sky. This phenomenon, which includes sunrise, the Sun reaching its highest point at local noon, and sunset, is not due to the Sun orbiting Earth. Instead, it is a direct consequence of Earth’s continuous rotation on its axis. As Earth spins, different parts of its surface are exposed to the Sun, creating the cycle of day and night.
Earth completes one full rotation approximately every 24 hours, causing the illusion that the Sun is moving around us. This constant turning makes it seem as though the Sun is sweeping across the heavens. The consistent rhythm of this rotation governs the division of our days.
How the Sun’s Position Changes Seasonally
Beyond its daily cycle, the Sun’s apparent path across the sky shifts over the course of a year, leading to distinct seasons. This yearly variation is primarily caused by Earth’s axial tilt, approximately 23.5 degrees relative to its orbital plane around the Sun. As Earth orbits the Sun, this tilt means different hemispheres receive varying amounts of direct sunlight.
One hemisphere tilted toward the Sun experiences longer days and more intense sunlight, resulting in summer. Conversely, the hemisphere tilted away receives less direct light and has shorter days, leading to winter.
Solstices mark when a hemisphere is at its maximum tilt toward or away from the Sun, yielding the longest or shortest daylight periods. Equinoxes occur when Earth’s axis is neither tilted toward nor away from the Sun, resulting in nearly equal day and night hours globally.
Earth travels at an average speed of about 108,000 kilometers per hour (67,000 miles per hour) in its elliptical orbit around the Sun. While Earth’s orbit is not perfectly circular, slight changes in distance from the Sun have a minimal effect on seasonal temperatures compared to the axial tilt. The tilt dictates how high the Sun appears in the sky and the duration of daylight, driving the seasonal changes we observe.
The Sun’s Journey Through the Galaxy
While the Sun’s daily and seasonal movements are apparent from Earth, the Sun itself is in constant motion through space, carrying the entire solar system with it. It orbits the supermassive black hole at the center of the Milky Way galaxy.
This galactic journey occurs at an immense speed. The Sun’s orbital speed around the galactic center is approximately 220 kilometers per second (about 490,000 miles per hour). Despite this speed, it takes an exceptionally long time for the Sun to complete one full revolution. This complete orbit, known as a galactic year or cosmic year, is estimated to last between 225 and 250 million Earth years.
As the Sun moves through the galaxy, it does not follow a perfectly flat path. It also oscillates vertically through the galactic plane. This motion is influenced by the gravitational pull of other stars, gas, and dust within the galactic disk. The Sun’s movement is a complex, three-dimensional process within the Milky Way galaxy.