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.

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.

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.

How far away are stars?

The nearest star to the earth is our own sun, which is 152 million km away. After the sun, the closest stars are Proxima Centauri and Barnard's star. The farthest stars in our galaxy are 80000 light years away. Other galaxies, each one containing millions of stars, are much more distant.

How does a Star die?

Stars die when they eventually use up all their fuel and burn out, but this process takes many millions of years. Towards the end of its life, a star starts to run out of hydrogen to power its nuclear fusion. It starts to cool, becoming a red giant. The red giant swells, and the pressure at its centre becomes so great that the star begins absorb energy instead of emitting it. In a matter of seconds the star collapses, then explodes into a supernova. This is a huge explosion of light and energy that can be seen right across the galaxy.

How big are Stars?

Our sun is quite a small star, even though is measures 1392530 km across, which is 109 more than the earth's diameter. If the sun were the size of a football, The earth would only be 2mm across. Some stars are known as Superiants. The star Antares, for example, is 700 times bigger than the sun. There is a star in the constellation of Auriga that may be 3000 million km in diameter, which is also known as 4000 times bigger than our sun. The neutron star that remains after the eplosion of a supernova may only be 20 km in diameter, but of enormous mass. If it weighs more than 2 or 3 times that of our sun, it begins to collapse into a black hole.

What is a star?

Stars are huge balls of burning gas that are scattered throughout the universe. They burn for millions of years, giving off both light and heat. Stars produce energy by a process called Nuclear fusion. The coldest stars are coloured red and are dim, while the hottest stars give off blue-white light. The temperatures on the surface range from 3500 degrees celcius for the coldest star to over 40000 degrees celcius for the hottest star. A new star is born when gas and dust are drawn together by gravity, forming a huge clump. It heats up until Nuclear Fusion begins, and the new star appears.

What is the Milky Way?

The Milky Way is a huge mass of gas and stars that can be clearly seen as a band of light across the night sky. The earth, and everything else in the Solar System, is part of the Milky Way. It is known as our galaxy. It is so huge that light takes nearly 100000 years to travel from one side to the other. Where stars are packed close together, the Milky Way is bright in that particular spot, but huge clouds of gas and dust block the light from the other parts ofthe galaxy. These clouds prevent astronamers from observing the whole Milky Way.