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 Phases of
the Moon
The revolution of the Moon around the
Earth makes the Moon appear as if it is changing shape in the sky.
This is caused by the different angles from which we see the bright part
of the Moon's surface. These are called "phases" of the Moon. Of course,
the Moon doesn't generate any light itself; it just reflects the light
of the Sun. The Moon passes through four major shapes during a
cycle that repeats itself every 29.5 days. The phases always
follow one another in the same order. Below are pictures of the
four major shapes and a description of each.
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New Moon: The lighted side of the Moon
faces away from the Earth. This means that the Sun, Earth, and
Moon are almost in a straight line, with the Moon in between the Sun
and the Earth. The Moon that we see looks very dark.
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First Quarter: The right half of the Moon
appears lighted and the left side of the Moon appears dark.
During the time between the New Moon and the First Quarter Moon, the
part of the Moon that appears lighted gets larger and larger every
day, and will continue to grow until the Full Moon.
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Full Moon: The lighted side of the Moon
faces the Earth. This means that the Earth, Sun, and Moon are
nearly in a straight line, with the Earth in the middle. The
Moon that we see is very bright from the sunlight reflecting off it.
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Last Quarter: Sometimes called Third Quarter.
The left half of the Moon appears lighted, and the right side of the
Moon appears dark. During the time between the Full Moon and
the Last Quarter Moon, the part of the Moon that appears lighted
gets smaller and smaller every day. It will continue to shrink until
the New Moon, when the cycle starts all over again.
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Questions:
- What phase is the Moon closest to
right now?
- Go to this site. When will
there be a Full Moon this month? When will there be a New Moon
this month?
- Based on the calendar at the
above Internet site, and the fact that it takes about 29.5 days for
the Moon Cycle to repeat, see if you can predict when the next Full
Moon and New Moon will be (for help, use a calendar). Go to
the Space
Academy and use the Moon Phase Applet to check your answers.
- Now, repeat questions 2 and 3 for
the First Quarter Moon and Last Quarter Moon.
There are also four other phases of
the Moon sometimes used. They are as follows:
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This
is known as a Waxing Crescent Moon. This Moon can be seen after the New
Moon, but before the First Quarter Moon. The crescent will
grow larger and larger every day, until the Moon looks like the
First Quarter Moon.
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This
Moon is known as a Waxing Gibbous
Moon. This Moon can be seen after the First Quarter Moon, but
before the Full Moon. The amount of the Moon that we can see
will grow larger and larger every day. ("Waxing"
means increasing, or growing larger.)
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This
Moon is called a Waning Gibbous Moon.
This Moon can be seen after the Full Moon, but before the Last
Quarter Moon. The amount of the Moon that we can see will grow
smaller and smaller every day. ("Waning" means decreasing,
or growing smaller.)
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This
Moon is called the Waning Crescent
Moon. This Moon can be seen after the Last Quarter Moon and
before the New Moon. The crescent will grow smaller and
smaller every day, until the Moon looks like the New Moon.
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Do you feel you understand the Phases
of the Moon? Then take the Phases
of the Moon quiz at NASA's StarChild
Project website!
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