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Explanation
of the Moon
Phases
The phases
of the moon
are caused
by the
relative
positions of
the earth,
sun, and
moon. The
moon goes
around the
earth, on
average, in
27 days 7
hours 43
minutes.
The sun
always
illuminates
the half of
the moon
facing the
sun (except
during lunar
eclipses,
when the
moon passes
thru the
earth's
shadow).
When the sun
and moon are
on opposite
sides of the
earth, the
moon appears
"full" to
us, a
bright,
round disk.
When the
moon is
between the
earth and
the sun, it
appears
dark, a
"new" moon.
In between,
the moon's
illuminated
surface
appears to
grow (wax)
to full,
then
decreases
(wanes) to
the next new
moon.
The edge of
the shadow
(the
terminator)
is always
curved,
being an
oblique view
of a circle,
giving the
moon its
familiar
crescent
shape.
Because the
"horns" of
the moon at
the ends of
the crescent
are always
facing away
from the
setting or
rising sun,
they always
point upward
in the sky.
It is fun to
watch for
paintings
and pictures
which show
an
"impossible
moon" with
the horns
pointed
downwards.
Above
information
courtesy of
NASA
http://liftoff.msfc.nasa.gov |
