Look at the full moon tonight, and again next month. You will see the same dark patches in the same places. In fact, people have always seen the same face of the Moon. Why does it never turn around to show us its back?
The Moon does spin
You might think the Moon does not spin at all. It does! But it spins at the same rate at which it travels around the Earth. So by the time it has gone once around us, it has also turned around exactly once. This keeps the same side always facing Earth. Scientists call this tidal locking.
Try it yourself: walk in a circle around a chair while always facing the chair. When you get back to the start, you have turned all the way around, but the chair only ever saw your face!
The “dark side” is not dark
You may have heard people talk about the “dark side of the Moon”. That name is a mistake. No part of the Moon stays dark all the time. The side we never see gets sunlight too; it just faces away from us. Scientists call it the far side. It looks quite different from the near side, without the large dark patches, called maria, that we see from Earth.
A dusty grey mirror
The Moon does not shine on its own. It reflects sunlight, and not very well! Its surface reflects only about 12 per cent of the light that falls on it, a little more than old, worn road tar.
The Moon also has almost no air. With no wind or rain to wear them away, its craters stay for a very long time. Twelve astronauts have walked on the Moon, starting with Neil Armstrong and Buzz Aldrin in 1969.
Slowly drifting away
On average, the Moon is about 3.8 lakh kilometres from Earth. Walking there at an average pace, without ever stopping, would take around nine years! And it is slowly moving away from us, by about 3.8 centimetres every year. Do not worry: that is far too slow for anyone to notice in a lifetime.
Wonder about: If you stood on the far side of the Moon, could you ever see the Earth in the sky?