Earth has just one Moon. It goes around Earth in a path called an orbit. Why does the Moon look different from night to night, and what happens in an eclipse? Let's find out.
We always see the same side of the Moon from Earth. People sometimes call the far side of the Moon the dark side, but that is misleading, because the far side gets sunlight too. Until a Soviet spacecraft flew past in 1959, nobody had seen the far side of the Moon.
The Moon does not make its own light. It shines because it reflects sunlight. The Sun always lights half of the Moon, but how much of that lit half we can see from Earth changes during the month. The Moon's shape does not really change during the month.
The Moon's phases happen because the Moon, Earth and Sun change positions as the Moon orbits Earth. The Moon goes through eight phases, from new Moon to full Moon and back again. Waxing means the lit part of the Moon that we see is growing, and waning means it is shrinking.
At a new Moon, we can hardly see the Moon at all. At a full Moon, we can see all of the Moon's sunlit side. Between them, we see only part of the lit side.
It takes about 29.5 days to go from one new Moon to the next, or from one full Moon to the next. A calendar month is about the length of time from one full Moon to the next.
A lunar eclipse happens when Earth's shadow falls on the Moon. During a total lunar eclipse, the Moon can look red or orange.
A solar eclipse happens when the Moon passes between the Sun and Earth. That can only happen at a new Moon.
Words to know
- phases: Moon looks
- waxing: growing
- waning: shrinking
- eclipse: shadow event
- reflects: bounces back
The short version
The Moon does not make its own light. It shines by reflecting sunlight. Its shape does not really change during the month. What changes is how much of its sunlit side we can see from Earth, and the phases happen as the Moon, Earth and Sun change positions.
Quick facts
- The Moon goes through eight phases, from new Moon to full Moon and back again.
- It takes about 29.5 days to go from one new Moon to the next.
- Waxing means the lit part we see is growing, and waning means it is shrinking.
- A lunar eclipse happens when Earth's shadow falls on the Moon.
- A solar eclipse happens when the Moon passes between the Sun and Earth, which can only happen at a new Moon.
Does the Moon really change shape?
No. The Moon's shape does not really change during the month. What changes is how much of its sunlit side we can see from Earth.
Do Earth's shadows cause the Moon's phases?
No. Phases happen because the Moon, Earth and Sun change positions as the Moon orbits Earth. Earth's shadow falls on the Moon only during a lunar eclipse.
