page_title: Moon
section_title: Phases
hierarchical_section_title: Moon / Phases
context_page_description: The Moon is Earth's largest natural satellite, and we usually see it in the night sky. Some other planets also have moons or natural satellites.
  Our moon is about a quarter the size of the Earth. Because it is far away it looks small, about half a degree wide. The gravity on the moon is one-sixth of the Earth's gravity. It means that something will be one-sixth as heavy on the Moon than on Earth. The Moon is a rocky and dusty place. The Moon moves slowly away from the earth at a rate of 3.8 cm per year, due to the effect of tidal dissipation.
context_section_description: The Moon being round, half of it is lit up by the sun. As it goes around (or orbits) the Earth, sometimes the side that people on Earth can see is all lit brightly. Other times only a small part of the side we see is lit. This is because the Moon does not send out its own light. People only see the parts that are being lit by sunlight. These different stages are called Phases of the Moon.
  It takes the Moon about 29.53 days (29 days, 12 hours, 44 minutes) to complete the cycle, from big and bright to small and dim and back to big and bright. The phase when the Moon passes between the Earth and Sun is called the new moon. The next phase of the moon is called the "waxing crescent", followed by the "first quarter", "waxing gibbous", then to a full moon.  A full Moon occurs when the moon and sun are on opposite sides of the Earth.  As the Moon continues its orbit it becomes a "waning gibbous", "third quarter", "waning crescent", and finally back to a new moon. People used the moon to measure time. A month is approximately equal in time to a lunar cycle.
  The moon always shows the same side to Earth. Astronomers call this phenomenon tidal locking. This means that half of it can never be seen from Earth. The side facing away from Earth is called the far side or dark side of the Moon even though the sun does shine on it—we just never see it lit.
caption: The phases of the Moon
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