Why does the moon seem to change shape each month?

The shape of the moon alters depending on the position of the sun in relation to the moon. The sun lights up only one side of the moon. As the moon orbits the earth, we see this lit up area from different angles. When the sun is almost behind the earth, it lights up the whole of the moon (this is called a full moon). When the sun is off to one side, part of the moon is in deep shadow and all we can see is a thin slice, or crescent, of the moon's lit surface.

What is the moon?

The moon is earth's only satelite, and it hes been orbiting our planet for at least 4000 million years. It is a rocky sphere about 3476 km in diameter, which is about a quarter size of the earth. scientists believe that the moon was formed when another planet about the size of Mars collided with the earth. The collision splashed a huge mass of molten rock into space. This molten rock quickly formed into a sphere, and the moon rapidly cooled into its solid form. The moon's surface is heavily pitted by collisions with debris, such as asteroids.

Why is Europa especially interesting?

Europa is one of Jupiter's moons. In 1979 the Voyager spacecraft passed by Europa and found that it had a very smooth surface covered with ice. It has very few craters, which has led astronamers to suspect that there may be liquid water beneath the surface. In theory, there might even be a form of primitive life hidden beneath the ice, where water remains as a liquid.

Do other planets have Moons?

Apart from the earth, most of the other planets have Moons although these are usually quite small. Saturn has the most Moons, it has at least 18 Moons. Some of these are very strange. Enceladus has a smooth surface covered with shiny beads of ice that make it shine and glitter. Lapetus is black on one side and white on the other. Jupiter has 16 moons, four of which are very large. One of Jupiter's moons is larger than Mercury and the other 3 are larger than our moon.. Charon, which orbits Pluto, is either a large moon or a small companion planet.

What makes Neptune blue?

Neptune is covered with a blue ocean of liquid methane gas. It is a very cold place, its surface temperature drops to -210 degrees celcius. Neptune is made of Hydrogen, Helium and Methane, and probably has a rocky core. It takes an amazing 164.8 years to travel just once around the sun. Neptune was first identified in 1846 when astronamers found that an unidentified planet was disturbing the orbit of Uranus. Neptune has huge storms and one of these, the Great Dark Spot, was larger than the earth.

Which are the outer planets?

Uranus, Neptune and Pluto are the outer planets. They are so far away that they were discovered only when powerful telescopes were developed. Pluto, the smallest of the planets, is on the edge of deep space. It was only discovered in 1930, as a result of mathematical calculations to find out why Neptune's orbit was being disturbed by an unknown body. Pluto has an oval orbit that occasionally takes it inside the orbit of Neptune. As recently as 1978 scientists found that Pluto, which is only 2284km across, has an even smaller companion planet or moon, called Charon.

What are the rings of Saturn?

Shining rings of billions of tiny chips of ice, rock and dust surround saturn. The rings reflect light strongly and can be clearly seen through a telescope from the earth. It was first thought that Saturn had three wide rings, but it is now known that the rings are actually made of thousands of narrow ringlets. The rings are only 100m thick, but they extend into space for 76000km. The material in the rings was probably captured by saturns gravity when the Solar System was forming, or it might be the remains of a moon that has broken up. Recently space probes discovered that some of the rings are braided, or twisted, but so far there is no explanation for this strange effect.

Where is the largest known canyon?

It is on Mars of course. There is no running water to wear away the rock landscape on Mars, so huge valleys can survive for millions of years. A system of enormous canyons called the Valles Marineris (Mariner Valleys) was discovered by the space probe Mariner 9. The canyon is more than 4000 km long and 4 times as deep as the Grand Canyon in USA. Scientists think that these valleys were caused by erosion (wearing away). During storms, the gritty martian dust is blasted by winds reaching up to 450 km/h, wearing away softer rock.

Could we live on Venus?

Science fiction writers thought that life might exist beneath the thick clouds covering Venus. We now know that conditions there are too extreme for life as we know it. Robot spacecraft have landed on Venus and studied its atmosphere, which is mostly poisonous Carbon Dioxide and Sulphuric acid. We cannot see the planet's surface through its thick atmosphere, but enough sunlight gets through to raise the surface temperature to 480 degrees celcius. This atmosphere reflects sunlight, making Venus very bright when viewed from earth.

What are the inner planets?

The four planets that are nearest to the sun are called the inner planets. In order from the sun, they are Mercury, Venus, Earth and Mars. The inner planets are different from the outer planets, which are farther away from the sun, because they are made from rock. The outer planets are mostly composed of gas. Each of the inner planets has an atmosphere. However, apart from the earth's atmosphere, the atmosphere's of the inner planets are very thin and would be poisonous to humans.

Which planet is closest to the sun?

Mercury is the closest planet to the sun. The temperature on the side of the planet facing the sun is as high as 430 degrees celcius. The shaded side of Mercury which faces away from the sun is bitterly cold at -180 degrees celcius. Mercury has almost no atmosphere because it has been burned off by the sun. The planet consists of bare rock, pitted and scarred by the impact of meteorites. It has extremely steep cliffs that are hundreds of kilometres long. These were formes when the planet cooled from its original molten (liquid) state, millions of years ago.

How old is the Universe?

It is possible to calculate the approximate age of the universe by looking at how fast dist galaxies are moving away from us. However, it is not possible for us to make this calculation accurately. Scientists have estimated that the universe is between 13000-18000 million years old.