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The Solar System

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The Milky Way is a containing billions of stars. The Sun is one of these stars.

The Sun is the largest object in the Solar System. The Sun's huge gravitational field keeps many other objects - planets, dwarf planets, asteroids and comets - in orbit around it.

The Earth is one of eight planets in the Solar System. The planets orbit the Sun at different distances.

The different planets have different properties and conditions. In general, as the distance from the Sun increases:

the temperature decreases, for example, Mercury is 430 °C whereas Neptune is -200 °C

the time taken to orbit the Sun increases, for example, Mercury orbits once every 88 Earth days, but Neptune orbits once every 165 Earth years

For a planet to form, its own gravity must be strong enough to make it round or spherical in shape. Its gravitational field must also be strong enough to 'clear the neighbourhood', pulling smaller nearby objects into its orbit.

Moons are natural that orbit a planet. Many planets have moons, and some planets have many moons - Saturn has more than 50. The Earth has just one moon - the Moon.

Dwarf planets

Pluto is a . The gravitational field of a dwarf planet is not strong enough to clear the neighbourhood, so there may be other objects in its orbit around the Sun. The Solar System contains hundreds of dwarf planets, including Ceres (the only dwarf planet in the asteroid belt).

The Solar System contains smaller objects called - these orbit the Sun in highly orbits, which are oval or egg-shaped and may take millions of years to complete. Asteroids are made of metals and rocky material. There are large numbers of asteroids orbiting the Sun in the asteroid belt between Mars and Jupiter. There are also many in a region beyond Neptune called the Kuiper Belt.

The Solar System also contains small objects called . Comets are similar to asteroids, but are made of rocky material, dust and ice. As a comet approaches the Sun, it begins to , which means that it turns into a gas. It then produces a distinctive tail.

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Structure of the Solar System - The Solar System - AQA - GCSE Physics (Single Science) Revision - AQA - BBC Bitesize

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The Milky Way is a containing billions of stars. The Sun is one of these stars. The Sun is the largest object in the Solar System. The Sun's huge gravitational field keeps many other objects - planets, dwarf planets, asteroids and comets - in orbit around it.

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The Life Cycle of a Star

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The formation and life cycle of stars - The life cycle of a star - AQA - GCSE Physics (Single Science) Revision - AQA - BBC Bitesize

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Learn about and revise the life cycle of stars, main sequence stars and supernovae with GCSE Bitesize Physics.

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The Expanding Universe

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Light from a star does not contain all the wavelengths of the electromagnetic spectrum . Elements in the star absorb some of the emitted wavelengths, so dark lines are present when the spectrum is analysed. Different elements produce different patterns of dark lines. The diagram shows part of the emission spectrum of light from the Sun.

Spectra from distant galaxies

Astronomers can observe light from distant . When they do this, they see it is different to the light from the Sun. The dark lines in the spectra from distant galaxies show an increase in wavelength. The lines are moved or shifted towards the red end of the spectrum. This effect is called . The diagram shows part of the emission spectrum of light from a distant galaxy.

Red-shift and speed

Astronomers see red-shift in virtually all galaxies. It is a result of the space between the Earth and the galaxies expanding. This expansion stretches out the light waves during their journey to us, shifting them towards the red end of the spectrum. The more red-shifted the light from a galaxy is, the faster the galaxy is moving away from Earth.

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Red-shift - The expanding Universe - AQA - GCSE Physics (Single Science) Revision - AQA - BBC Bitesize

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Light from a star does not contain all the wavelengths of the electromagnetic spectrum . Elements in the star absorb some of the emitted wavelengths, so dark lines are present when the spectrum is analysed. Different elements produce different patterns of dark lines. The diagram shows part of the emission spectrum of light from the Sun.

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Sample Exam Questions

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Multiple choice questions are perhaps the easiest to complete - you simply put a cross in a box - however, the questions often have two answers that could, at first glance, be correct. Don't make the mistake of reading the first answer and thinking this is correct without checking all the others.

If it says 'Tick box', you must tick one box. If you leave it blank or tick two or more boxes, you will get zero marks. These multiple choice questions will not start with command words like 'Describe...' or 'Explain...'. They will be written in the form of a question like or .

There will be more multiple choice questions on the Foundation paper.
This page contains AQA material which is reproduced by permission of AQA.

Sample question 2 - Foundation

Complete the following sentence by drawing a ring around the correct option.

The fact that light from a distant galaxy seems to move towards the red end of the spectrum gives scientists evidence that ...

C
As distant galaxies move away, the wavelengths of light waves emitted are stretched by the motion of the galaxy, making them longer. Red light is the longest wavelength of light in the visible spectrum so we say the waves have been red-shifted as they appear closer to the red end of the spectrum than they would do if the galaxy was not moving. Red-shift is detected in light from all galaxies, so they must all be moving away from each other, meaning that the Universe is expanding.

Sample question 3 - Higher

Use the correct answer from the box to complete the sentence.

Energy is released in stars by the process of nuclear ______.

Fusion
Within stars, smaller atoms like hydrogen are fused together into larger atoms like helium. Fission occurs in nuclear reactors when large atoms are split and nuclear decay releases a form of nuclear radiation.

Sample question 4 - Higher

The discovery of cosmic microwave background radiation was important because it ...

The 'Big Bang' theory has not been proven but the detection of cosmic microwave background radiation provided more evidence for the 'Big Bang' theory that could not be explained by the 'Steady State' theory.

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Space physics - Multiple choice questions - Sample exam questions - AQA - GCSE Physics (Single Science) Revision - AQA - BBC Bitesize

# data[].attributes.attachment_link.description
Multiple choice questions are perhaps the easiest to complete - you simply put a cross in a box - however, the questions often have two answers that could, at first glance, be correct. Don't make the mistake of reading the first answer and thinking this is correct without checking all the others.