Cosmic Candles Shine a Light on the Size of the Universe

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For a hundred years, astronomers have been trying to pin down the exact distance to one of our nearest neighbouring galaxies, the Large Magellanic Cloud. Measuring distances in the vast Universe is very tricky business: we can't travel with a measuring tape, and our rulers would have to be very long! However, astronomers have come up with some very clever tricks for measuring distances, using just light.

In the case of the Large Magellanic Cloud, its distance was determined by looking at pairs of stars that orbit each other. We call these 'binary systems'; you can see an artist's impression of one in this picture. From Earth, we see the stars regularly passing in front of each other. Each time this happens, the combined brightness of the stars drops. By tracking the changes in brightness very carefully, astronomers can work out all kinds of information: how big the stars are, how much material they have and even how far they are from Earth!

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