Imagine you’re in a spaceship, traveling away from Earth. As you sail onward, you see our planet and its Moon locked together in their endless, circling, gravitational embrace. Your distant view gives you a unique perspective on the Moon that can be hard to visualize from the ground, where the Moon appears to sweep through the sky as an ever-changing globe of light.
From your astronaut’s viewpoint, you can see that the Moon is an average of 238,855 miles (384,399 km) from Earth, or about the space that could be occupied by 30 Earths. It travels around our planet once every 27.322 days in an elliptical orbit, an elongated circle. The Moon is tidally locked with Earth, which means that it spins on its axis exactly once each time it orbits our planet. Because of this, people on Earth only ever see one side of the Moon. We call this motion synchronous rotation.
The Moon’s orbit is tilted about 5 degrees compared to the plane of Earth’s orbit around the Sun. Because of this tilt, the Moon as seen from Earth’s perspective usually passes above or below the Sun when it passes between us and the Sun. The tilt of the Moon’s orbit prevents us from having monthly solar and lunar eclipses.
Now let’s travel back to Earth to explore how this affects our view of the Moon in the sky...