The Moon's Changing Face
The Moon is Earth's only natural satellite. As it travels around our planet, it appears to change shape in the sky. These changing shapes are called the phases of the Moon.
Why We See Phases
The Moon does not produce its own light. We see the Moon because it reflects sunlight. The phases we see depend on how much of the sunlit side of the Moon is facing us as it orbits the Earth. It takes the Moon about 29.5 days to go through a full cycle of phases, which is the basis for our month.
As the Moon waxes, the sunlit portion we see is growing. As it wanes, the sunlit portion is shrinking.
The Eight Major Phases
1.New Moon: The Moon is between the Earth and the Sun. The side facing us is not lit up, so we can't see the Moon.
2.Waxing Crescent: We see a small sliver of the sunlit side.
3.First Quarter: We see half of the sunlit side (it looks like a half-moon).
4.Waxing Gibbous: We see more than half of the sunlit side.
5.Full Moon: The Earth is between the Sun and the Moon. The entire side of the Moon facing us is lit up.
6.Waning Gibbous: The lit portion starts to shrink. We still see more than half.
7.Third Quarter (or Last Quarter): We again see half of the sunlit side, but it's the opposite half from the First Quarter.
8.Waning Crescent: We see only a small sliver again, just before the cycle returns to the New Moon.
Eclipses: Cosmic Shadows
An eclipse occurs when one celestial body, such as a moon or planet, moves into the shadow of another celestial body. The two types of eclipses involving the Sun, Earth, and Moon are solar and lunar eclipses.
Solar Eclipse
What it is: A solar eclipse occurs when the Moon passes directly between the Sun and Earth, and the Moon's shadow is cast upon the Earth.
Alignment: Sun → Moon → Earth
Phase: This can only happen during a New Moon.
Effect: From a small area on Earth, the Moon completely blocks the Sun's light, creating a temporary darkness during the day.
Lunar Eclipse
What it is: A lunar eclipse occurs when the Earth passes directly between the Sun and the Moon, and the Earth's shadow obscures the Moon or makes it look reddish.
Alignment: Sun → Earth → Moon
Phase: This can only happen during a Full Moon.
Effect: The Moon passes through the Earth's shadow. The Moon often appears red because some sunlight is filtered and refracted through Earth's atmosphere before reaching the Moon.
Why don't we have eclipses every month? Because the Moon's orbit is tilted slightly relative to the Earth's orbit around the Sun. The perfect alignment needed for an eclipse only happens a few times a year.