What's the biggest star?

Carolin - Taking biggest mean size, now we’re talking diameter of stars, the most reliable estimate I can give you is a star that's just short of 4000 light years away. It’s a red supergiant called VY Canis Majoris and its diameter is somewhere between about fourteen hundred to two thousand times the diameter of the sun, which means its volume is three billion times the volume of the sun. And you know these are all large numbers but...

Chris - That’s a big star, that could give Justin Bieber a run for his money

Carolin - Well, if workout that if you traveled round its circumference at the speed of light it would take you six hours to go once round. Whereas if you did the same thing with our sun it would just take you a hundred forty five seconds. Now, so that's a lot bigger but there is an interesting question here is, how do we know the diameter of this star? Because even when you look through telescope most stars just look like points. A star like this that's big and relatively near you can sometimes resolve the disk and even measure the angular size of the disk, you know how far away the star is, you got a triangle and you can measure the width of the disk. But once further away you can't actually see the disk and you have to be quite clever so you have to do some physics to infer it for most of the stars. So even though there could be some stars which may be larger, the most reliable estimate is the VY Canis Majoris at the minute.