How long is one complete rotation of the moon

The Earth's gravitational force on the moon distorts the moon into a slightly prolate, or football, shape; in addition the moon's intrinsic form is somewhat egg-shaped. The Earth's gravity maintained this spin state even as other gravitational interactions caused the moon to move outward to its present orbital radius. Sign up for our email newsletter. Already a subscriber? Sign in. It also takes approximately 27 days for the moon to rotate once on its axis.

As a result, the moon does not seem to be spinning but appears to observers from Earth to be keeping almost perfectly still. Scientists call this synchronous rotation. The side of the moon that perpetually faces Earth is known as the near side. The opposite or "back" side is the far side. Sometimes the far side is called the dark side of the moon, but this is inaccurate.

When the moon is between the Earth and the sun, during one of the moon phases called the new moon, the back side of the moon is bathed in daylight. The orbit and the rotation aren't perfectly matched, however.

The moon travels around the Earth in an elliptical orbit , a slightly stretched-out circle. When the moon is closest to Earth, its rotation is slower than its journey through space, allowing observers to see an additional 8 degrees on the eastern side. When the moon is farthest, the rotation is faster, so an additional 8 degrees are visible on the western side.

Related: The moon: 10 surprising lunar facts. A "moon day" is around In other words, whereas Earth completes one rotation every 24 hours, the moon experiences a sunrise roughly every hours. As with many celestial bodies, the moon's rotating motion may be a remnant from its creation.

One theory, called the giant-impact hypothesis, proposes that around 4. This theoretical object is known as Theia, and the heat from Theia's impact may have created magma oceans by melting the Earth's crust and caused Earth to eject spinning vaporized particles into space.

Related: How long would it take to walk around the moon? According to the giant-impact hypothesis, these clouds of dust and gas were spinning from the force of the original collision. Eventually, these swirling particles came together, because mass attracts mass, and as the gas condensed it actually began to spin faster. Consider a figure skater who tucks their arms in as they spin on the ice.

The skater's mass is more compact closer to their middle, so the skater speeds up. This is because their angular momentum is conserved — a product of the rotational force needed to rotate an object, or the moment of inertia, and angular velocity. The leading theory is that a Mars-sized object collided with Earth billions of years ago, and debris from this collision eventually formed the Moon. Here is an animation that shows what this might have looked like:. Animation showing the Moon's early history.

For more information, visit The Moon In Depth web page. The Moon does have gravity. Earth would be a very different world if it had no Moon. Some of your frequently asked Moon questions, answered. Does the Moon spin on its axis? Why does the Moon rise and set? Can people in different countries see the Moon on the same day? Here is an animation that shows what this might have looked like: Animation showing the Moon's early history. The Moon plays a starring role. Like Earth, the Moon has a day side and a night side, which change as the Moon rotates.