Space

‘That’s one small step for a man,’

The icy surface of Europa

Scientists are very excited about this. One day, they hope to send a space probe to Europa. When the probe lands, it will use radar to look for water under the ice. ‘We have already done this sort of thing on the Earth,’ says astronomer Chris Chyba. ‘There’s a lake in Antarctica that’s under 4 kilometres of ice. It’s called Lake Vostok – and it was discovered with radar. So that’s what we could do on Europa, and I think we probably will.’

If they find the ocean, they will send a submarine down into it. And that will be very exciting indeed. When the submarine turns on its lights, what will it see? Huge fish, with no eyes and enormous teeth? Nobody knows. But scientists want to find out.

Another moon which may have life is Titan. Titan is Saturn’s biggest moon; it is bigger than the planet Mercury. In fact, Titan probably was a planet once, before it came too near Saturn. It is different from all Saturn’s other moons, because it goes around

Inside a very large star the temperature gets hotter and hotter. Hydrogen turns to helium, and then into other things – carbon, oxygen, and iron. But then, one day, the star becomes too hot, and there is not enough hydrogen left. Then, very suddenly, the star collapses. As it collapses, it gets even hotter still, and then it explodes. In the explosion, the temperature may reach 100 billion °C.

This exploding star is called a supernova. One day in the next million years, Betelgeuse, that big red star in Orion, will explode like this. In fact, it is possible that it exploded a hundred years ago, and is already a supernova. But the light from the explosion has not reached us yet, so we cannot see it.

When the light from a really big supernova does reach the Earth, it is really exciting. Sometimes people can see the supernova in daylight. People in Japan and China saw a supernova like this in 1024 AD, and people in England saw one in 1604 AD.

millions, billions, or even hundreds of billions, all in the same part of space.

If you try to count all these stars and galaxies, you reach an impossible number. The scientist Carl Sagan said, ‘The total number of stars in the universe is larger than all the grains of sand on all the beaches of the planet Earth.’

the same way. We know from this that they formed as part of the spiral when the Sun became a star.

All of these planets and asteroids go around the Sun in

Jupiter and Saturn are mostly made of gas. Uranus and Neptune are mostly made of ice.

tance around the middle of the Earth. They are much further away from the Sun, so they take longer to move around it.

Then there are four more planets – Jupiter, Saturn, Uranus, and Neptune. These are all much bigger; for example, the distance around the middle of Jupiter is eleven times the dis

In the beginning
How many stars can you see in the night sky? In a city, you probably cannot see very many. But on a clear night, far from city lights, you can see hundreds, perhaps several thousand. With a telescope, you can see many thousands. With a really good telescope, scientists can see hundreds of millions.

But look closer: as well as stars, there are galaxies out there. What is a galaxy? It is a group of stars – millions, billions, or even hundreds of billions, all in the same part of space.

If you try to count all these stars and galaxies, you reach an impossible number. The scientist Carl Sagan said, ‘The total number of stars in the universe is larger than all the grains of sand on all the beaches of the planet Earth.’

So where did all these stars and galaxies come from? How were they made? Today, space is very big – enormously big – but scientists say that between 12 and 14 billion years ago, space was really small, impossibly small. Everything in the universe was pushed together in a space smaller than a full stop.

Then there was a BIG BANG and everything in the universe began to move away from the explosion at enormous speed. (This idea about the beginning of the universe is often called the Big Bang.) There were clouds of hot gas – hydrogen and helium. As they flew through space, over millions of years, these gases began to move around in spirals, like water going out of a bath. Many pictures of galaxies have this spiral shape.

Inside the big spirals of each galaxy there were millions of smaller spirals, which formed into huge burning balls, and each burning ball was a star. And all these galaxies are still moving away from each other at enormous speed, so space is getting bigger and bigger all the time.

So how big is space? Well, it is much bigger than we can easily understand. But, amazingly, we can use our eyes to see how big it is.

Look at the group of stars called Orion. On a clear night, you can see these easily without a telescope. The star at the top left is a red star called Betelgeuse. The star at the bottom