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Space facts and terminology

Take a look at our space and astronomy definitions.
The Solar System.
© Royal Observatory Greenwich

We appreciate that there is a lot of terminology in astronomy that you may not be familiar with. We introduced you to some of that terminology in Week 1 when we asked you to explain what an asteroid is. We showed you how to explain words related to asteroids in our Space Rocks video.

Here are some useful words to help you navigate your way through the field of astronomy. We have provided some example analogies to help you understand and explain these terms to your class.

Create some of your own explanations and analogies for the rest of the list

  1. Red giant star A star that has used up its main fuel (hydrogen) and has expanded and cooled down, turning red. Our Sun will become a red giant in 5 billion years time. If you blow up a balloon you see the rubber stretch as it gets bigger and its colour becomes diluted or fainter. When stars die they expand and their surface (made of gas) becomes redder – this means they are getting cooler. On a gas cooker the blue part of the flame is hottest and the orange/red part of the flame is cooler (although still too hot to touch!).

  2. Galaxy A large group of stars – at least 100 million. Our Milky Way galaxy has 400 billion stars (a four with eleven zeros after it!) and looks like a big spiral. If you shake a snow globe, all the bits of snow (or glitter) swirl around but then eventually settle to the bottom because of gravity. In a galaxy all the stars tend to swirl around the centre, where the gravity is strongest. They can look like a frisbee or flat spinning top or Catherine wheel. Some look like a giant orange rugby ball and others look very messy because they collided with another galaxy.

  3. Black hole A dead star that was once much much bigger than the Sun. Their gravity is so strong that even light can’t escape; this is why they are black. When you take a bath or have a shower – water swirls around the plug hole and then eventually falls in due to gravity pulling it down. If a star gets too close to a black hole it gets pulled apart until its gas swirls around the black hole and eventually it gets pulled in and squashed.

  4. The Big Bang The beginning of time and space – the birth of our universe. We do not believe that time or space (or matter or light) existed before the Big Bang. The Universe is a bit like an inflating balloon with coins stuck on the surface. As the balloon gets bigger the coins move further apart from each other. Our universe is expanding and galaxies are moving apart.

  5. Exoplanet

  6. Comet

  7. Solar eclipse

  8. Meteor shower

© Royal Observatory Greenwich
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Our Solar System and Beyond: Teaching Primary Science

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