Why does the Moon change shape?


Bizarre: The Moon is a large ball of rock that doesn’t change shape- it just looks as though it does. The shape we see in the sky today depends on how much of the Moon’s face is lit up. Sometimes we observe a thin crescent, and at other times we see half or three quarters of the Moon, and then a fully lit face- a Full Moon.

The view we have of the Moon changes according to the relative positions of the Sun, Earth and Moon. A complete cycle of shape, known as phases, takes 29.5 days.

How the Moon was formed?

Most astronomers think that the Moon was formed out of Earth about 4.5 billion years ago. It is known as the giant-impact theory.

  1. A Mars- sized asteroid collides into Earth at a speed of 20 km per sec (12 miles per sec).
  2. Smashed asteroid pieces and material gouged out of Earth’s rocky mantle for a ring around Earth.
  3. Over several millions years, the pieces of orbiting material bump into each other and join together.
  4. They form one large body- the Moon. About a quarter the size of the Earth, it slowly moves out of its present orbit.

Fast Facts

  1. The pull of the Earth’s gravity keeps the Moon in orbit.
  2. The Moon’s surface gravity is about one-sixth of Earth’s.
  3. The Moon’s gravity pulls on Earth’s oceans to produce tides.
  4. The Moon reflects light like a very dirty mirror. Although the Full Moon looks bright, it is 400,000 times dimmer than the Sun.
  5. The Moon is 400 times smaller than the Sun but as it is 400 times closer they look the same size.
  6. The Moon’s surface temperature changes every Moon- day from hotter than boiling water to colder than liquid air.