How Earth Orbits the Sun

Earth constantly moves through space on a path around the Sun. This motion is called an orbit. Earth follows a slightly elliptical path, which means the orbit is shaped like a stretched circle rather than a perfect circle. Our planet completes one full trip around the Sun every 365.25 days. This time period defines one year on Earth.

Earth travels at an incredible speed during its journey around the Sun. Scientists have measured that our planet moves at about 67,000 miles per hour through space. Despite this tremendous speed, we do not feel the motion because everything on Earth moves together at the same rate. The force of gravity from the Sun keeps Earth in its orbital path. Gravity acts like an invisible rope that pulls Earth toward the Sun. However, Earth's forward motion prevents it from falling into the Sun.

The combination of Earth's orbit and its axial tilt creates the seasons we experience. Earth's axis tilts at an angle of 23.5 degrees compared to its orbital path. As Earth moves around the Sun, different parts of the planet lean toward or away from the Sun at different times. When the Northern Hemisphere tilts toward the Sun, it receives more direct sunlight and experiences summer. At the same time, the Southern Hemisphere tilts away and experiences winter. Six months later, the positions reverse.

Evidence from satellite observations shows that Earth maintains a relatively stable orbit. The distance between Earth and the Sun varies slightly throughout the year because of the elliptical shape. Earth comes closest to the Sun in January at about 91 million miles. It reaches its farthest point in July at about 94 million miles. This difference in distance is small compared to the total orbital path. The tilt of Earth's axis affects seasons much more than the changing distance does.

Understanding Earth's orbit helps scientists explain many patterns we observe. The revolution of Earth around the Sun combined with Earth's rotation on its axis creates our calendar system. The extra quarter day each year is why we add a leap day every four years. Without this adjustment, our calendar would slowly drift out of alignment with the seasons. Earth's predictable orbital motion allows scientists to calculate the positions of planets and plan space missions years in advance.

Interesting Fact: Because Earth travels in an elliptical orbit, the Sun appears slightly larger in our sky during January when Earth is closest. The difference is only about 3 percent, which is too small for most people to notice without special equipment.