Double Award - Science for GCSE

The Earth and beyond

1.	Stars, galaxies and the Universe Our Sun is a small star. It is the nearest star to Earth. Stars are sources of heat and light. Millions upon millions of stars cluster together to form a galaxy and billions of galaxies make up the whole Universe. Most of the stars we see at night are in our own galaxy which is called the Milky Way. The study of stars, planets and other bodies in the sky is called astronomy. Astronomical distances are so huge that they are measured in light years. A light year is the distance travelled by light in one year (1016 metres). The distance across our galaxy (the Milky Way) is 100 000 light years.
2.	The Solar System The cartoon on the right will help you to remember the order of the planets from the Sun. Our Solar System has nine planets which orbit the Sun. The Sun is huge compared to its planets. All nine planets move in elliptical orbits and in the same direction around the Sun. They are all in the same plane, except Pluto whose orbit is at an angle to this plane. The four inner planets nearest the Sun – Mercury, Venus, Earth and Mars – have hard, rocky surfaces with thin atmospheres. The next four planets – Jupiter, Saturn, Uranus and Neptune – are much larger planets with small, rocky cores surrounded by thick gas. Pluto, furthest from the Sun, is a very small, rocky planet. Between the inner and outer planets is a band of rocky bodies (like tiny planets) which is also orbiting the Sun. These rocky bodies are called asteroids.
3.	The conditions on a planet are affected by two major factors. Its distance from the Sun, which determines the surface temperature and the evaporation of volatile substances. Its relative size, which determines the gravitational pull on its atmosphere.
4.	Forces of gravity Forces of gravity (gravitational forces) act between all masses. These gravitational forces increase: – as the masses increase; – as the masses get closer together. Gravitational forces from the Sun are very strong. The pull of gravity from the Sun keeps all the planets in their orbits. Gravity also holds the Moon in orbit around the Earth, and gravitational forces from the Earth cause your weight.
5.	Satellites A satellite is something which orbits a planet. Moons are ‘natural’ satellites. Artificial satellites have four main uses. – Communication – TV, radio and telephone signals. – Monitoring – weather forecasting, mapping, spying. – Research – e.g. the Hubble telescope. – Navigation – for ships, aircraft and explorers.
6.	The evolution of stars is shown in the diagram below.
7.	Evolution of the Universe The American astronomer, Edwin Hubble, was the first to investigate other galaxies beyond the Milky Way. Hubble made two very important observations. - Light from other galaxies had longer wavelengths than expected. Hubble called this the red shift because the wavelengths of light from other galaxies moved towards the red end of the spectrum. Hubble explained this observation by suggesting that other galaxies are moving away from us. - The further a galaxy is from Earth, the greater is its red shift. This is called Hubble's Law. Hubble explained this second observation by suggesting that galaxies further away are moving away faster. Hubble's observations and explanations support the 'Big Bang' theory for the origin of the Universe. Since the 'Big Bang', the Universe has been expanding and cooling as galaxies move away from each other.