What is a light–year?

Although the year is a time measurement unit, the light-year is not used to measure time. Actually it measures distances. The distances between stars are so big that to measure the distance between them we have to replace the Kilometre by the light-year. So, a light–year corresponds to the distance that light covers during a year.

What distance does a light–year correspond to?

The speed of light is about 300,000 kilometres per second. So, 1 light–second corresponds to 300,000 kilometres. In order to find the distance that exists in a light–year, you just have to calculate the amount of seconds that exists in a year and then multiply by 300,000. We have solved it and the result is 9,460,800,000,000, this is, 9 trillions 460 billion and 800 million kilometres. It is a really big number, isn’t it?!

In order to have an idea about what that distance represents, we can say that the Moon is only 1 light–second away from our Planet and the Sun is at the distance of 8 light-minutes. The Sirius Star, one of the most shining in the sky, is at a distance of eight light–years from the Earth (when we look at that star, we are watching how it was like eight years ago). The closest galaxy of the Milky Way, the Andromeda, is about 2.5 million light–years away from our Planet. I invite you to face a challenge: try to convert that distance into kilometres!

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