The Phases of the Moon.
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How Do the Phases Get Their Names?
When the Moon appears smaller than a quarter, we call it a crescent.
When the Moon appears larger than a quarter, we call it gibbous. When
the moon is getting bigger (phases New to Full) it is waxing. When it
is getting smaller (phases Full to New) it is waning.
For example, if today the Moon were a waxing
crescent, then tomorrow the crescent shape would continue to
grow larger, approaching first quarter. After first
quarter, the Moon would be a waxing gibbous, and
continue growing until it reached full. The Moon
would then begin to shrink, becoming first a waning
gibbous and eventually reaching third
quarter. Following third quarter it becomes a waning
crescent, and continues to shrink until it becomes invisible
at new Moon.
Just in case you can't remember all of this, there are a few handy
ways to recognize whether the Moon is growing or shrinking. A
crescent moon which looks like a "C" is shrinking (C for collapsing!).
If it looks like a "D", then it is growing. This is true for a
gibbous Moon as well, but it's a bit trickier to picture. If the edge
of the Moon (the real edge of the Moon, not the edge of night on the
Moon) is curved like a "C", the gibbous Moon is shrinking. Another
way to think of it is that the Moon always grows or shrinks from the
right to the left.
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