On the line – July 2008

Transcript

Rob: Hello. My name is Rob Edwards, and I'm here with Dr Claire Bretherton of the Royal Observatory, Greenwich. I'm going to be asking Claire a selection of questions that we've received after our live planetarium shows. With an eclipse coming on 1 August, these questions will be themed around the Sun.

My first question for you, Claire, is: how was the Sun formed?

Claire: Well, the Sun was formed out of a huge cloud of gas and dust, and gravity started pulling this gas and dust together. And as it got pulled further and further together by gravity, it got very condensed, it started to heat up and started to spin, really, quite quickly. And when this gas and dust in the center reached around 10 million degrees, it was able to start nuclear reactions. So it could therefore turn hydrogen, the simplest thing in the universe, into helium, and produce huge amounts of heat and huge amounts of light.

Rob: My next question for you is: will our Sun die?

Claire: Well, all stars die eventually. When our Sun gets towards the end of its life, when it runs out of fuel to burn, first of all, it's going to bloat into a red giant. At that stage, it will reach out at least as far as the orbit of Mercury, at least as far as the orbit of Venus - perhaps even as far as the orbit of the Earth. But don't worry about it just yet. It's going to be another five billion years, at least, before our Sun reaches that stage.

Once it's become a red giant, the Sun will then gently puff its outer layers out into space, forming a beautiful planetary nebula. The central parts of the star become compressed together and form what we call a white dwarf star, which is a very hot but dead star. It will weigh almost as much as the Sun but only be about the size of the Earth. And over billions and billions of years, this white dwarf star will gradually cool down, until we can no longer see it.

Rob: So our Sun won't explode, then?

Claire: No. Our Sun's actually far too small. Although it seems really big, and it is big - you can fit the Earth inside it a million times over - compared to many other stars, it's just a normal, average star. In order for a star to explode when it dies, it would have to be at least eight to ten times the mass of our Sun.

Rob: My final question is: what can you tell me about the upcoming eclipse?

Claire: Well, actually, on 1 August this year, there's going to be an eclipse of the Sun. In some parts of the world, it will be a total eclipse, so the Sun will be completely covered by the Moon. Here in Britain, it will only be partial.

And what happens is that the Moon passes in between the Earth and the Sun. Although the Moon is much smaller than the Sun, it's actually much, much closer to us as well, and so it just about covers the whole of the Sun in the sky during the total eclipse. So what will happen is we'll see a slice taken out of the Sun as the Moon moves across.

Rob: About what time will the eclipse take place?

Claire: Well, it starts at around 20 past nine in the morning, finishing at about 11.20pm.

Rob: What can you tell people about how to view an eclipse safely?

Claire: Well, first of all, you must never, never look directly at the Sun, because it's going to do a lot of damage to your eyes. There are special viewers that you can buy that will help you look more safely. But really, the best way is to try and project the eclipse onto another surface -- so, either using a pinhole and projecting it onto a sheet of white paper or even just looking at the reflection in a bucket of water.

Rob: Claire, thank you very much.