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.


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