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The Moon does not make its own light. It reflects light from the Sun.
The dusty surface of the Moon reflects only about 12 percent of the Sun’s rays. But that’s enough to make it shine brightly. However, we don’t see all of it from Earth all the time.
The only part of the Moon we see is what gets lit by the Sun. During a full Moon, the Sun is shining right on the Moon. But at all other times, Earth is in the way. That’s why we can only see part of the Moon. The Moon waxes, or grows, while going from new (dark) to full Moon. It wanes, or shrinks, when going from a full Moon to a new one. ▼
Light moves across the Moon’s surface. In a waning Moon, the light gets dimmer from right to left. In a waxing Moon, it gets brighter from right to left.
▲ The time the Moon takes to rotate, or turn on its axis, is 27.32 days. That’s the same amount of time it takes to orbit Earth. This means the Moon is in a synchronous rotation with Earth. One side of the Moon, the near side, always faces Earth. The far side is the part of the Moon we can’t see. ▼
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◀ A new Moon looks nearly or totally dark from Earth. It happens when the Moon is between Earth and the Sun. Then, the light from the Sun falls on the far side of the Moon. The side that faces Earth is dark, so we can’t see the Moon.
▲ Earth circles the Sun as the Moon circles Earth in an oval-shaped orbit. That’s also called an elliptical orbit. Our view of the sunlit part of the Moon changes as it orbits Earth. That’s why it looks like the Moon changes shape. These changes are known as phases. A phase cycle goes from one new Moon to the next. It takes about 29.5 days. Why is there a difference between the length of one phase cycle and the time the Moon takes to orbit Earth? The Moon has to move those extra days to catch up with the moving Sun.
Eclipses
When the shadow of one object in space falls on another, it makes an eclipse. During one, you cannot see what’s in the shadow. A solar eclipse is when the Moon blocks the Sun’s light from an area on Earth. A lunar eclipse is when Earth blocks the Sun’s light from the Moon. When do eclipses happen? Only when the Moon crosses Earth’s orbit at a certain point. The Sun, Moon, and Earth have to be lined up. So they only happen during a new or full Moon. ▼
Total Solar Eclipse
The Moon blocks out the whole Sun. The only part of the Sun that shows is a ring of light called a corona.
Annular Eclipse
Sometimes the Moon is at a far point in its orbit of Earth. Then, it can’t totally block the Sun. That leaves an annulus, a ring that is brighter than a corona.
Total Lunar Eclipse
The Moon moves into Earth’s shadow, also called an umbra. Most of the time, the Moon does not totally disappear during a lunar eclipse. Instead, it usually turns red. A little sunlight reflects off Earth. It bends in the atmosphere and then bounces off the Moon.
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Partial Solar Eclipse
In this eclipse, the Moon covers only part of the Sun.
Partial Lunar Eclipse
The Moon passes through part of Earth’s shadow.
