Each
month our Moon passes through eight phases. These phases are
named after how much of the moon we can see, and whether the
amount visible is increasing, or decreasing each day.
It takes the our Moon about 29.5 days to completely cycle through all
eight phases. Occasionally (about every 2.7 years) there are two Full
Moons in the same month. This is referred to as a Blue Moon. Hence the
saying "Once in a Blue Moon".
New
Moon
The
side of the moon facing the Earth is not illuminated. Additionally,
the moon is up through out the day, and down through out
the night. For these reasons we can not see the moon during
this phase.
Waxing
Crescent
During
this phase, part of the Moon is beginning to show. This
lunar sliver can be seen each evening for a few minutes
just after sunset. We say that the Moon is "waxing" because
each night a little bit more is visible for a little bit
longer.
First
Quarter
During
first quarter, 1/2 of the moon is visible for the first
half of the evening, and then goes down, leaving the sky
very dark.
Waxing
Gibbous
When
most of the Moon is visible we say it is a Gibbous Moon.
Observers can see all but a little sliver of the moon.
During this phase, the Moon remains in the sky most of
the night.
Full
Moon
When
we can observe the entire face of the moon, we call it
a Full Moon. A full moon will rise just as the evening
begins, and will set about the time morning is ushered
in.
Waning
Gibbous
Like
the Waxing Gibbous Moon, during this phase, we can see
all but a sliver of the Moon. The difference is that instead
of seeing more of the Moon each night, we begin to see
less and less of the Moon each night. This is what the
word "waning" means.
Last
Quarter
During
a Last Quarter Moon we can see exactly 1/2 of the Moon's
lighted surface.
Waning
Crescent
Finally,
during a Waning Crescent Moon, observers on Earth can only
see a small sliver of the Moon, and only just before morning.
Each night less of the Moon is visible for less time.
You
Can See Jupiter's Moons Tonight!!
With an inexpensive pair of binoculars anyone
can easily see Jupiter's four largest moons.
These
moons are Callisto, Ganymede, Europa, and Io. These fascinating
worlds were discovered by Galileo in the early 1600's.
Ganymede
is larger then both the planets Mercury and Pluto, Europa has
a liquid water ocean, and Io is covered with powerfully explosive
volcanoes.
Through
your binoculars, these worlds will look like small stars. First
find Jupiter, then use the chart to the left to help you identify
each moon.
