The Monthly Cycle of the Moon
- Friday, June 11, 2004
At mid-month, the Moon is "behind" the Earth in its orbit, in the position opposite the Sun. At this time, the entire bright side is turned toward the Earth, and so the Moon is "Full." Wall calendars show the Full Moon phase as a white circle. Since it is opposite the Sun, the Full Moon rises in the East as the Sun sets in the west. After rising, the Full Moon can be seen in the sky the entire night. If you're up a couple hours before sunrise, you can see the Full Moon setting in the west as the Sun once again rises in the east.
After the Full Moon, the Moon again begins to move out from behind the Earth. At this time, the Moon is "waning" which means it is "decreasing" in phase. The Waning Moon will draw a little closer again to the Sun with each passing day, and it will then become a little thinner in phase. Also, in the days past the Full Moon, the Waning Moon rises after the sunset. You can see it rising later and later each night, an average of 48 minutes later than the night before.
In this way, the Waning Moon is still visible in the morning sky before the sunrise. After the Full, you can see a waning gibbous Moon in the morning sky around sunrise. However, in the waning phases, the Moon's bright edge is the opposite from that seen in the waxing phases.
About a week after the Full Moon, the Moon has once again waned to a half moon visible high up in the morning sky. By this time, the Moon is three-quarters finished with its monthly cycle of phases, and this phase is thus called "Last Quarter." The Last Quarter Moon is shown on wall calendars as a circle half black and half white. But in this phase, the white and black halves are on opposite sides from how they were shown at First Quarter, to correspond with the actual appearances of the Moon.
And after Last Quarter, the month draws to an end as the waning crescent of the old Moon moves a little closer to the sunrise each morning, growing a little thinner in phase. The Moon's cycle is completed as it vanishes in the morning glare of the sunrise, and at the next New Moon another lunar month begins.
The cycle of the Moon's phases is one of the topics illustrated in "Cycles," my educational comic book, now available from the Classical Astronomy Store. Click here: http://store.classicalastronomy.com/shop/view.php?id=1
Jay Ryan is the author of "The Classical Astronomy Update," a free e-mail newsletter for helping Christian homeschool families learn more about events in the starry sky. If you would like to receive the Update, please drop Jay an e-mail at firstname.lastname@example.org. Visit the Classical Astronomy web site – www.ClassicalAstronomy.com
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