Why does it take 27.3 days

The Moon does not make its own light. All moonlight is reflected sunlight. The bright part of the Moon is experiencing daytime. The Moon is a natural satellite , or a space object that orbits around something else. In general, a moon is a natural satellite of a planet, and a planet is a special kind of natural satellite that orbits a star and also meets other conditions.

Learn more: What makes a planet a planet? 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. This is because the Earth is moving around the Sun. The Moon has to travel a bit further to get back to the same position. The Moon is "tidally locked" into position with the Earth. One side always faces the Earth, and the other side always faces away. This is because it takes the same amount of time to spin on its axis once as it does to orbit the Earth once.

This is called a sidereal month. It represents the orbital period of the Moon around the Earth. Measuring the motion of the Moon around the Earth relative to the Sun leads us to what is called the synodic pronounced si-nod-ik period.

The synodic period is the time required for a body within the solar system, such as a planet, the Moon, or an artificial Earth satellite , to return to the same or approximately the same position relative to the Sun as seen by an observer on the Earth.

The Moon's synodic period is the time between successive recurrences of the same phase; e. What causes a lunar eclipse? Pictures of the Moon's phases often make it look like there should be a lunar eclipse during each full Moon and a solar eclipse during each new Moon.

However, two things have to happen for a full lunar eclipse. First, the Moon has to be full, so there is only an opportunity for a lunar eclipse about once each month. Second, the Moon has to pass through Earth's shadow. This means that most of the time the Moon is slightly above or below Earth's plane of orbit — and out of the shadow cast by Earth where it blocks the Sun's light.

No eclipse occurs during these full Moons. But two to four times each year, a full Moon occurs when the Moon's orbit intersects Earth's plane of orbit, placing the Moon in Earth's shadow — and a lunar eclipse occurs! How long does it take our Moon to go around Earth? It takes 27 days, 7 hours, and 43 minutes for our Moon to complete one full orbit around Earth. However, it takes our Moon about This is called the synodic month.

The difference between the sidereal and synodic months occurs because as our Moon moves around Earth, the Earth also moves around our Sun.