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Moon basics

The Moon is the nearest celestial body to the Earth at an average distance of 400,000 km. It has a diameter of 3476 km, about one quarter that of the Earth.

Internal structure of the Moon
Internal structure of the Moon

The Moon has a crust (C) which is around 60 km thick on the near side and even thicker on the far side. The mantle (B) extends down to a depth of 1000 km. A semi-molten core (A) is probably in the centre, but unlike the Earth does not provide a global magnetic field.

Astronomers currently believe that the Moon was formed after a Mars-sized body collided with the Earth during the early history of the solar system. The Moon then coalesced out of the debris from the impact.

The Moon has no appreciable atmosphere to protect it from the Sun's radiation or meteorite impacts. There is no liquid water and hence no prospect that life survives on or inside the Moon.

Days and nights on the Moon are 14 times as long as those on the Earth. Together with the lack of atmosphere, this means the surface experiences a huge range of temperatures, from a minimum of -170°C to a maximum of +130°C.

Questions to think about

1. Why does the Moon not have an atmosphere? What is an observational proof of this?

2. Describe some of the achievements of robotic and crewed spacecraft that visited the Moon. Do you think people should return to the Moon and establish colonies? Outline the arguments for and against this idea.

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