How To Understand Light Years
Question
what is the distance to the nearest star?
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I'm Robert Massey and I'm here from the Royal Astronomical Society which is one of the biggest astronomical organizations in the world and we look after the interests of astronomers not just in the UK but across the world. What I'm going to do today is give you a few pointers to get you started in astronomy which I think is one of the most incredibly interesting subjects there is. The universe is so big that sometimes units like kilometres don't really catch it. If you want to measure the distances to stars and other galaxies, you have to use a completely different set of distance scales. The one that is quite familiar to astronomers is the light year and that's how far light travels in a year. Now, to give you a sense of scale, the nearest stars are about four and a half light years away and that means that it's taken four and a half years for the light to reach us from those stars so you can see straight away this is a very long way, and light, each second, travels 300,000 kilometres. So in a year, given about 31 million seconds, light travels something like nine and a half trillion kilometres so even the nearest stars are more than 40 trillion kilometres away. The universe is really very big and that's why we don't use units like kilometres, we have to scale up to light years. When we use light years, distances become a bit more manageable but still get to be pretty big pretty quickly. The nearest stars are four and a half light years away but if we were to go right out to other galaxies, we can be talking tens of thousands, hundreds of thousands, and very quickly, millions and tens of millions of light years. The universe is simply so big that we have to use even bigger units to cover those distances. .