|Why does the moon change shapes?|
|Question Date: 2016-08-31|
The moon does not actually change
shapes. However when you go out at night, at
time each night and find the moon, you will note
that it presents a different aspect. This is
called the phase of the moon. The phase of
the moon occurs because the moon rotates around
the earth once a month and so the amount of
sunlight that reflects off the moon varies.
So, when the moon is between the earth and SUN we
have a new moon . . . we can not see it because
the side of the moon we face is NOT ILLUMINATED by
phases of the moon
Then, two weeks later we have a FULL MOON
because now the moon is on the opposite side of
the EARTH and sunlight keeps the disc of the moon
It doesn't. The moon is round, just like the
The phases of the moon happen because, just
like the earth, half of the moon is lit by the sun
(i.e. day), and the other half is shaded (i.e.
night). We see the moon's day side as light
because the sun is shining on it, and can't see
the night side so easily because it's dark. As the
moon orbits the earth, the moon can either get
between the earth and sun (new moon), or on the
opposite side of the Earth from the sun (full
moon), or anything in-between.
The moon is a sphere (like a ball) that orbits
around the earth. It takes around a month for the
moon to orbit (map a lap) around the earth. As
the moon moves around the earth, the moon phase
changes (new moon, crescent moon, half moon
etc.). It's shape is always the same (a
sphere), but when we see a half-moon or a
crescent-moon it is because we are only seeing
part of the moon and the rest is in shadow.
Think of when you're at the movie theater when the
lights are out and the screen is brightly lit up.
When someone in the audience stands you can't see
their face because they are in silhouette -- you
can see their shape but you can't see their
features because they are in shadow. This is
exactly the same as what happens when we are
looking at the moon. Depending on how the sun,
earth and moon are aligned, different parts of the
moon are in silhouette.
As a science experiment, try to look at
the moon every night for a month and see if you
can watch the different moon phases.
The Moon does not change shape, but the
shadow of the Moon crosses our view of it and
makes it seem to "wax and wane". A "Waxing
Moon" means the Moon appears to be growing
(becoming more lit-up), and a "Waning Moon" means
the Moon appears to be getting less light
(becoming darker). We can only see one side of
the Moon's surface at a time from our home on
The Moon orbits around the Earth every 27 days.
There are some days when the Moon is between the
Earth and the Sun (and there are some days when
the Earth is between the Moon and the Sun). When
the Moon is between the Earth and the Sun, then
the Moon's shadow (created by the Sun's light),
falls toward the Earth's surface, and we see a
"New Moon" (when the Moon is dark or
completely covered in shadow). After every New
Moon, the shadow will start to disappear from our
view of the Moon's surface. This is because the
Moon moves away from its spot between the Earth
and the Sun, and the Sun begins to shine on the
Moon's surface (the side we can see from Earth).
As the Moon orbits around the Earth, the surface
that we can see will have more and more light
(from the Sun) shining on it until it becomes a
"Full Moon" (which is the opposite of a New
After every Full Moon, the Moon begins to wane
(or get darker) because it is moving toward the
Sun and has less and less sunshine hitting the
visible surface. This is the Waning Moon
stage. It is during this time that we see the
Moon change from Full, to half-full (called
"Quarter Moon"), to a crescent-shape
(called "Crescent Moon"), and finally back
to a New Moon (completely covered in shadow).
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