The Moon is Earth’s only natural satellite, a dry, cratered world that always turns the same face to us and the only place beyond Earth that people have walked.
At a glance
| radius | 1,740 km (0.273 × Earth) |
|---|---|
| distance from its planet | 384,000 km |
| one orbit | 27.3 days |
| reflects | 12% of the sunlight it gets |
Read off the piece’s own catalogue, the same values it draws with.
About Moon
The Moon is rocky and airless, its face divided into bright, heavily cratered highlands and dark maria, plains of ancient lava that flooded great impact basins. Earth’s gravity long ago slowed its spin until it turned once per orbit, which is why we always see the same side. Its gravity in turn raises the tides of Earth’s oceans.
The Apollo astronauts brought back rocks that dated its surface and revealed a composition close to Earth’s mantle. The leading explanation is that the Moon formed from debris thrown out when a Mars-sized body struck the young Earth. Mirrors left on the surface still reflect laser pulses fired from Earth, timing the distance precisely and showing that the Moon is slowly moving away.
By coincidence the Moon and the Sun appear almost the same size in our sky, which is why the Moon can cover the Sun exactly in a total solar eclipse and reveal the faint corona around it.
What you see in the piece
The Moon is drawn with its real surface map, its maria and highlands lit only by sunlight, so its phases appear on their own as it goes round Earth. From the Sun’s neighbours, neither it nor Earth can be seen at all.
Measured or modelled
The giant-impact origin is the leading model and explains much, but the near-identical composition of the Moon and Earth is still not fully reproduced by simulations.
Questions
How far away is the Moon?
On average about 384,000 km from Earth, and it goes round Earth once every 27.3 days.
Why do we always see the same side of the Moon?
Earth’s tides slowed the Moon’s spin until it turned exactly once per orbit. This tidal locking keeps the same face pointed towards us.