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The revolution of the Moon around the Earth causes the Moon to appear to change shape in the sky. These apparently different shapes are called "phases" of the Moon. The Moon passes through a cycle of eight phases which repeats itself every 29½ days. There is no definite starting point for the cycle, but phases follow one behind the other in a strict order.

Below you will find photographs of each of the eight Moon phases as well as the names and a brief description of each phase.



New Moon: lighted side of the Moon faces away from the Earth. New Moon
Waxing Crescent: a small part of the Moon appears lighted and grows larger on successive days. Waxing Crescent
First Quarter: the right half of the Moon appears lighted, with the lighted part growing larger on successive days. First Quarter
Waxing Gibbous: more than half of the Moon appears lighted, with more and more becoming lighted on successive days. Waxing Gibbous
Full Moon: lighted side of the Moon faces toward Earth. Full Moon
Waning Gibbous: more than half of the Moon appears lighted, with less and less becoming lighted on successive days. Waning Gibbous
Third Quarter: the left half of the Moon appears lighted, with the lighted part growing smaller on successive days. Third Quarter
Waning Crescent: a small part of the lighted Moon is visible and grows smaller on successive days. Waning Crescent
Source: NASA





Average Distance from Earth: 238,857 miles (384,500 km)
Diameter: 2,160 miles (3,476 km)
Mass: 7.35 X 1022 kg  (0.012 times Earth's mass)
Surface Gravity: 1.62 m/sec2 (0.166 times that of Earth)

(Thanks to the Moon's weak gravity, you would feel much lighter -- only about one-sixth your weight on Earth. If you weigh 180 pounds, you would weigh about 30 pounds on the Moon.)

Temperature variation:

Sunlit Side (Lunar "noon"): 243°F (117°C)

Dark Side (Lunar "midnight"): -279°F (-173°C)

Length of Lunar Day: 29.53 Earth days
Atmosphere: None

Because the Moon has no atmosphere, the sky is black, even during the day.

The Dark Side of the Moon:  People often refer to "the dark side of the moon", but there is no such thing.  The sun shines on all sides of it in turn.  However, there is a "far side of the moon" which is never seen from the earth.  Over the eons, the gravitational forces of the earth have slowed down the moon's rotation about its axis until the rotational period exactly matches the revolution period about the earth.




NASA Wavelength - Online science resource from NASA for teachers and students to help bring Earth, the solar system, and the universe into their schools and homes.
Current Moon Phase - See the current phase of the Moon or the phase of the Moon on a future or past date.
Moon Phase Applet - See how the phases of the Moon relate to the positions of the Earth, Moon, and Sun.
Tide Predictions - The Old Farmer's Almanac provides a Tidal Prediction calculator that allows you to find when it will be high tide in your area.
Phases of the Moon and Percent of the Moon Illuminated - U.S. Naval Observatory site about phases of the Moon, including a movie of the Moon progressing through one complete lunar cycle (one month).

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