Moons are the natural satellites of planets. Most are small rock globes that continually orbit the parent planet, held in place by the planet’s gravity. There are 65 known moons in the Solar System. Every planet in the Solar System has a moon, apart from Mercury and Venus, the nearest planets to the Sun. New moons are frequently discovered, as space probes such as the Voyagers reach distant planets.Three moons have atmospheres - Saturn’s moon Titan, Jupiter’s Io, and Neptune’s Triton. The Moon is 384,400 km from the Earth and about 25 percent of Earth’s size.
The Moon orbits the Earth once every month, with each orbit taking 27.3 days. It spins round once on its axis every 720 hours. The Moon is the only other world that humans have ever set foot on. Because the Moon has no atmosphere or wind, the footprints planted in its dusty surface in 1969 by the Apollo astronauts are still there today, perfectly preserved.
The Moon is the brightest object in the night sky, but it does not give out any light itself. It shines only because its light-coloured surface reflects sunlight. Only the side of the Moon lit by the Sun is bright enough to see. And because we see more of this side each month as the Moon orbits the Earth, and then less again, the Moon seems to change shape.
These changes are called the Moon’s phases. During the first half of each monthly cycle, the Moon waxes (grows) from a crescent-shaped new moon to a full moon. During the second half, it wanes (dwindles) back to a crescent-shaped old moon. A lunar month is the time between one full moon and the next.
This is slightly longer than the time the Moon takes to orbit the Earth because the Earth is also moving. The Moon has no atmosphere and its surface is simply grey dust, pitted with craters created by meteorites smashing into it early in its history. Planets On the Moon’s surface are large, dark patches called seas - because that is what people once believed they were.
They are, in fact, lava flows from ancient volcanoes. One side of the Moon is always turned away from us and is called its dark side. This is because the Moon spins round on its axis at exactly the same speed that it orbits the Earth. Unlike the Earth’s surface, which changes by the hour, the Moon’s dusty, crater-pitted surface has remained much the same for billions of years.
The only change happens when a meteorite smashes into it and creates a new crater. The Moons gravity is 17 percent of the earths, so astronauts in space suits canjump 4 m high! Laser measurements showed that, on average, the Moon is 376,275 km away from the Earth.
Gravity on the Moon is so weak that astronauts can leap high into the air wearing their heavy space suits. Temperatures reach 117°C at midday on the Moon, but plunge to -162°C at night. Moon landing The first Moon landing was by the unmanned Soviet probe Lunar 9, which touched down on the Moons surface in 1966.The first men to orbit the Moon were the astronauts on board the US Apollo 8 in 1968. On 20 July 1969 the American astronauts Neil Armstrong and Edwin (Buzz) Aldrin became the first men ever to walk on the Moon.
When Neil Armstrong stepped on to the Moon for the first time, he said these famous words: ‘That’s one small step for a man; one giant leap for mankind.’ Twelve men have landed on the Moon between 1969 and 1972. The Apollo 13 mission to the Moon suffered near tragedy when an explosion ripped through the service module.
The crew managed to return to Earth using the command module. The Moon astronauts brought back 380 kg of Moon rock. A mirror was left on the Moon’s surface to reflect a laser beam which measured the Moon’s distance from Earth with amazing accuracy.