Let us follow the Moon through its moves, beginning with its path. Earth has just one Moon, and it goes around Earth in a path called an orbit, but the path is not a circle. The Moon's distance from Earth changes as it moves on an oval orbit: on average about 363,300 km (225,700 miles) at its closest and about 405,500 km (252,000 miles) at its farthest. On average the Moon is about 239,000 miles (384,000 kilometers) from Earth, and it is less than a third as wide as Earth. It is also slowly drifting away from Earth, by about 1.5 inches (3.8 centimeters) each year.

The Moon takes about 27.3 days to circle Earth once, but about 29.5 days to go from new Moon to new Moon. A calendar month is about the length of time from one full Moon to the next. The Moon's phases happen because the Moon, Earth and Sun change positions as the Moon orbits Earth. Waxing means the lit part of the Moon that we see is growing, and waning means it is shrinking.

The Moon's shape does not really change during the month. 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 goes through eight phases, from new Moon to full Moon and back again. At first quarter we see half of the Moon's lit side, which is why it is called a quarter Moon. At a full Moon, we can see all of the Moon's sunlit side.

Here is a closer look at the Moon's spin. We always see the same side of the Moon from Earth, and people sometimes call the far side of the Moon the dark side, but that is misleading, because the far side gets sunlight too. The Moon spins exactly once for every trip it makes around Earth, which is why the same side always faces us, and this is called tidal locking. Even so, slight rocking and wobbling motions called librations let observers on Earth see as much as about 59% of its surface over time.

The Moon does not make its own light. A lunar eclipse happens when Earth's shadow falls on the Moon, and 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, which can only happen at a new Moon, when we can hardly see the Moon at all. We do not get an eclipse every month because the Moon's orbit is tilted compared with Earth's orbit around the Sun.

The Moon also moves the sea. The Moon's gravity pulls on Earth's oceans and is the main cause of the tides. Ocean water bulges out on the side of Earth nearest the Moon and on the side farthest from it, and these bulges are the high tides. Spring tides, the biggest tides, happen at new Moon and full Moon, when the Sun, Moon and Earth line up. Neap tides, which are moderate, happen around the first and third quarter Moon, when the Sun and Moon are at right angles to each other.

Words to know

• orbit: path around Earth
• librations: slight wobbles
• eclipse: shadow over light
• tides: sea level changes
• neap: moderate tide