moon phases - Moonstick Information Site

What Moon Phases Are

You probably know that the moon orbits the Earth. This just means that it is moving too slow to shoot off into infinity, but too fast to fall to the ground; it just circles the Earth. And of course, the sun is also out there is space somewhere. For now, you only need to know that the sun is much farther away (about 400 times farther). As we discussed, the moon makes circles around the Earth (about once every four weeks). As it makes its rounds, it passes alternately around the sunward and "dark" sides of the Earth. As the moon passes around the sunward side of the Earth, (as you might imagine) it is very hard to see in the blinding glare of the sun. At this time, it can (obviously) be seen only from the sunward (daytime) side of the Earth. About two weeks later, as the moon passes around the "dark" (nighttime) side of the Earth, it becomes much easier to see. It is no longer lost in the glare of the sun, plus its front side is illuminated by direct sunlight. During this time, the moon can (obviously) be seen only from the "dark" (nighttime) side of the Earth.

When the moon is on the sunward side of the Earth, it is said that the moon phase is "new moon". When the moon is on the "dark" side of the Earth, it is said that the moon phase is "full moon". The in-between phases are also named. When the moon crossing from the sunward side of the Earth into the "dark" side of the Earth, it is said that the moon phase is "first quarter". When the moon crossing from the "dark" side of the Earth into the sunward side of the Earth, it is said that the moon phase is "last quarter". The phases in-between these phases are also named. In chronological order, here are the names (and symbols) for the phases of the moon between two consecutive passes of the moon by the sunward side of the Earth.

new moon
young crescent (waxing crescent)
first quarter
waxing gibbous
full moon
waning gibbous
last quarter
old crescent (waning crescent)
new moon