Early astronomers thought that all the stars were the same distance from us, forming a simple shell around the Earth. Now we know that some stars are relatively close to us, and others are trillions of kilometres away.
Is it true? We measure how far the stars are in kilometres.
No. They’re so far away, that we use light years instead. A light year is how far light travels in one year – 9,461 billion km!
Are there candles in space?
Not really. But we can see how far away a galaxy is by the brightness of a special type of star, called a ‘standard candle’. The further away the galaxy, the dimmer the candle.
Amazing! Galaxies move so quickly they are different colours. The light waves from them change, just as a fire engine’s siren sounds lower after it zooms past. We use the colour to measure the galaxies’ speed.
How do you measure the distance to a star?
Watch the tip of your finger as you move it towards to your nose. The closer it gets, the more cross-eyed you become! Astronomers can tell the distance to a star by measuring how ‘cross-eyed’ a pair of telescopes has to be to see it.
Picture Credit : Google