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Category The Solar System

FORCES IN THE SOLAR SYSTEM

 

 

The planets travel round the Sun in nearly circular paths. So they are constantly changing direction. A force called ‘gravity’ makes the planets turn. You will have felt the force of the Earth’s gravity – without it you would float up into space! Gravity is a force which pulls. All the planets exert their gravity. The more massive they are, the stronger is their pull of gravity. The Sun is so massive that its gravity is strong enough to keep all the planets turning around it. Without this force, they would each fly off in a straight line.

The Moon also has gravity. Because it is less massive than the Earth, its pull of gravity is weaker – as the astronauts that landed on the Moon found out!

 

 

 

 

 

 

 

Force

Like the planets, this ball will keep moving in a circle as long as it travels fast enough. The force that acts along the string pulls the ball and makes it change direction. Although a different kind of force, its effect can be compared to the gravity exerted by the Sun. if the child let go of the string, there would be no pulling force to keep the ball turning. It would fly away in a straight line.

 

 

 

 

 

 

An astronaut leaps from the Moon’s surface while saluting the US flag.

VISITORS TO THE SOLAR SYSTEM

Occasionally we see ‘wanderers’ in our Solar System. A comet is a ball made of rock and ice. This nucleus is surrounded by a cloud of gas called the ‘coma’. When comets move close enough to the Sun. they reflect the Sun’s light and form a tail of gas and dust.

Comets leave bits of dust from their tails behind in space. Some of this dust enters the Earth’s atmosphere where it burns up. We may then see a shower of bright ‘shooting stars’. The scientific name for a shooting star is a ‘meteor’.

Sometimes lumps of rock or metal from space crash to the Earth. These are ‘meteorites’. A large meteorite may make a crater where it lands. Meteorites probably caused the craters on the surface of the Moon, Mercury and Mars – as well as this one in Arizona.

 

 

 

This meteor crater in Arizona is over 1 kilometre wide and 175 metres deep.

 

 

 

 

 

 

 

Halley’s Comet

Halley’s Comet is a regular visitor to our part of the Solar System. It returns about every 76 years and has been seen throughout the ages. The diagram shows the strange shape of the comet’s orbit – a long oval. The comet is invisible beyond Saturn’s orbit. You can see how the comet’s tail always points away from the Sun.

OBSERVING THE SOLAR SYSTEM

The planets and stars are far too far away to see clearly, however good your eyesight is. The telescope was invented to help people look at faint, distant objects and see them in more detail. Telescopes collect more light than the human eye. They can also make things look bigger. Stars looked at through a telescope seem to be brighter and closer.

Telescopes use either a lens or a mirror to collect light and focus it. Another lens is used to produce a magnified image. Modern telescopes are housed in giant buildings called ‘observatories’. These are often built at the top of a mountain where there is a clear view of the sky.

 

 

 

 

 

The telescope

This telescope uses one convex lens to collect and focus light, and another to magnify the image. Sliding the outer tube changes the distance between the two lenses. This is important as it allows you to see objects that are near and far away.

 

 

 

 

 

Looking down on a telescope in the observatory at Kitt Peak, Arizona, USA

EXPLORING THE SOLAR SYSTEM

Watching the Solar System from the Earth is one way of finding out about it. To learn more, people have used rockets to travel into space. There they have been able to look at parts of the Solar System more clearly. But although the first men landed on the Moon in 1969, no one has visited any of the planets. They are too far away and conditions are dangerous for humans.

However, as you have seen space probes – robot controlled unmanned spacecraft – have been sent far into the Solar System. The space probe Voyager 2 has travelled through the Solar System and is now well beyond the orbit of Pluto. As it travels it takes pictures and sends them back to Earth.

 

 

 

Voyager 2

This space probe gas already travelled across millions of kilometres of space, and has collected information on Jupiter, Saturn, Uranus and Neptune. The craft’s onboard computers are reprogrammed during its flight by electronic signals from Earth. The entire vehicle weighs only 815 kilograms. It carries equipment for 11 scientific experiments which are powered by a nuclear generator.

 

 

 

 

 

This is a photograph of the surface of Mars. The surface of Mars – you can see the solar panels of the lander at the bottom of the photo.

MORE ABOUT THE UNIVERSE

 

Life and death of a star

When a star like our Sun first forms it is different from the way we see it today. At first the Sun was a very hot, blue star. As it grew bigger it cooled down and looked white. The Sun will shine as it is for about 10,000 million years. Eventually it will swell and form a ‘Red Giant’. Some of the stars we see are Red Giants. They are cooler than the Sun. But as they are many times bigger, they appear brighter. A Red Giant slowly cools and shrinks. Its outer layers of gas drift away and a small hot star called a ‘White Dwarf’ is left. This slowly cools and becomes a ‘Black Dwarf’.

 

 

 

 

 

Very large stars

Stars much bigger than our Sun also become Red Giants, but they blow up in a huge explosion called a ‘supernova’. They shrink into themselves and form a ‘Black Hole’. Anything nearby gets sucked into a black hole. Even its own light cannot escape!