The Moon is a satellite that orbits around Earth. It is bigger than the dwarf planet Pluto, but it has no atmosphere. The ‘seas’ seen on the face of the Moon are craters made b y asteroids that crashed there 3,000 to 4,000 years ago. The Moon’s gravity causes the tides – the rising and falling of the Earth’s oceans and seas.
When the Moon is overhead, its gravity pulls the sea up to the shore. This is high tide. As Earth turns, the Moons pull weakens and the sea falls back to low tide.
The diameter of the Moon is 3,476 km and its orbit is 384,400 km from Earth. Its gravity is only one-sixth of the force of gravity produced by Earth.
When the Earth, Moon and sun shift apart, high tides are lower and low tides are higher. These are called neap tides.
When the Earth, Sun and Moon are in line, high tides are higher and low tides are lower. These are called spring tides.
The Moon’s face
The Moon rotates on its axis, but we see only one face. This is because Earth’s pull keeps one side of the Moon always in sight. The Moon rotates and orbits Earth in the same amount of time : 27.3 days.
Phases of the Moon
The Sun lights the orbiting Moon from different directions. At new Moon it lights the side we never see. The Moon passes through eight phases over 29.3 days. Six are shown here.
When a full moon occurs, the Sun and Moon are on opposite sides of Earth. A new moon ‘waxes’ – more of it is seen each day – until the full moon on day 14. Then it ‘wanes’ or grows thinner each day.
When a full Moon passes exactly behind the Earth, the Earth blocks sunlight from reaching the Moon. We see the Earth’s shadow pass over the Moon. This is called a lunar eclipse.
On the Moon
US space missions landed on the Moon six times between 1969 and 1972. Neil Armstrong was the first astronaut to walk on the Moon, on 21 July 1969. The Moon’s gravitational force is less than Earth’s, so the astronauts could easily jump across the landscape.