What is a Lunar Eclipse?

The earth casts a long shadow into space, and when this shadow passes over the moon it causes an Eclipse. A Lunar Eclipse can only happen during a full moon, when the sun is directly behind the earth. It happens only occasionally, because the orbit of the moon is slightly tilted and so the shadow misses it. Lunar eclipses can last for over 1 hour, but they do not completely black out the shadowed part of the moon. Some sunlight always filters through, making the shadow look a reddish-brown colour.

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.

What are meteorites made of?

Meteorites are made of rock or metal. They enter the earth's atmosphere at speeds of at least 11 km per second, which makes them glow brightly. Several thousand meteorites enter the earth atmosphere every year, but very few of them reach the ground. The largest known meteorite is made of iron and weighed 66 tonnes. It probably fell to the earth in prehistoric times in what is now Nambia, Southwest Africa. In general, it is hard to find meteorites. Recently, researchers have been locating them on the ice sheets in the Artic and the Antartic, where they are easier to find.

What happens when a meteorite hits the ground?

When a large meteorite hits the ground it can produce a crater. Meteorite craters are rare on earth, because the atmosphere slows the meteorite and also usually burns it up. Many ancient meteorite craters have been worn away by water and by weather over thousands of years. On planets and moons with no atmosphere, huge numbers of meteorites strike with enormous power. Our own moon is estimated to have 3000000 million meteorite craters measuring 1m or more in diameter. Some of the large geographical features on the moon and other planets and moons throughout the Solar System are probably the result of strikes by large meteors hitting their surfaces.

What is an Asteroid?

Asteroids are small rocky or ice bodies that orbit the sun. They are sometimes called minor planets. Most asteroids are found in an orbit between Mars and Jupiter, and more than 7000 of them have been identified. Asteroids are smaller than any of the planets, and only a few have a diameter of over 30 km. The term asteroid is usually applied to objects larger than 1.6 km in diamter. One asteroid, called Ida, has a tiny moon of its own; this is the smallest known satelite in the Solar System. Asteroids were probably formed at the same time as the planets

What is the tail of a Comet?

You cannot see the nucleus of a comet with the naked eye, but you can sometimes see its tail. It appears as a smear of light that moves very gradually across the night sky. As a comet moves closer to the sun, the ice and other frozen gases in its nucleus begin to boil off, producing a long tail of gas and dust. The tail always points away from the sun because light and other forms of radiation from the sun push against the minute particles that are present within the tail.

What is a comet?

Comets are often described as 'dirty snowballs'. The solid centre, or nucleus, of a comet consists mostly of ice mixed with sooty material. The nucleus is quite small and is usually only a few kilometres across. Comets travel around the sun in and elongated orbit. They plunge out into deep space beyond the farthest planet before diving back into the Solar System and passing close to the sun. As the comet's nucleus comes closer to the sun it becomes smaller and may eventually break up into small fragments. Comets are thought to be as old as the Solar Sytem itself.

What are shooting stars?

Shooting stars, or meteors, are streaks of light across the night sky, but they can be seen for only 1 or 2 seconds. They are caused when a solid piece of rock called a meteroid, plunges through the earth's atmosphere, burning up due to air friction. When the rock enters the atmosphere it is known as a meteor. If, as rarely happens, a small fragment reaches the earth, it is called a meteorite. The earth regularly passes through clouds of meteors orbiting the sun. The best known cloud, called the Perseids, reappears each year on August 12-13, sometimes producing spectacular meteor showers. There is also a regular meteor shower in December called the Geminids.

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 Sunspots?

Groups of black blotches appear on the sun every 11 years. These blotches are called Sunspots. They are areas that are about 1000 degrees celcius cooler than the rest of the sun's surface. Sunspots are caused by changes in the sun's magnetic field. When they appear, Sunspots cause radiation that often interferes with the radio and television signals on the earth. Some groups of Sunspots can be as much as 10 times the size of the 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.

Why do stars twinkle?

Most stars burn steadily, and if we could see them from space they would not be twinkling at all. This is because as the light from a star passes through the earth's atmosphere, it is bent by changes in the air temperature. This makes the light appear to flicker. Because of this effect, astronomical observatories are situated on mountain tops. Higher up, the air is thinner and it is therefore less likely to cause this twinkling effect.