Section 1 of 4Structure of the Universe
1
Planets orbit stars, and each star with its planets forms a solar system.
2
A galaxy is a very large collection of stars held together by gravity.
3
The Universe is the name given to the whole of space and everything in it, including all galaxies.
4
Estimates suggest that there are more than 100 billion galaxies in the Universe.
Section 2 of 4The Milky Way
Milky Way
- The galaxy that contains our Solar System, made up of billions of stars.
Position of the Sun
- The Sun is one of the billions of stars in the Milky Way, lying far from its centre.
Other stars
- Other stars in the Milky Way are much further from Earth than the Sun, and some have their own planets.
Neighbourhood
- Our Solar System is just one of potentially billions of systems in our galactic neighbourhood.
Section 3 of 4Earth's Place in Space
Earth's Place in Space
Earth
- The third planet from the Sun, orbiting within the Solar System that lies inside the Milky Way.
Solar System
- The Sun and everything gravitationally bound to it, including planets, moons, asteroids and comets.
Universe
- The whole of space and every galaxy within it, which is expanding.
Observation
- Astronomers study distant galaxies by analysing the light they emit.
Section 4 of 4Exam Checklist & Tips
8.2.2 – Key Points for the Exam
- Galaxy A large collection of stars held together by gravity.
- Universe The whole of space and all the matter and galaxies within it.
- Solar System The Sun together with the planets and other objects that orbit it.
- Milky Way The galaxy that contains the Sun and our Solar System.
- Star A large ball of gas that releases energy by nuclear fusion.
Common Mistakes
- Using universe and galaxy as if they mean the same thing;
- a galaxy is one large collection within the Universe.
- Thinking the Milky Way is the only galaxy; there are billions of galaxies in the Universe.
- Describing the Solar System as containing other stars; it contains only the Sun and objects that orbit it.