The answer to this is acid catalysed oxidation. If you add oxygen and ultraviolet light to most things, like hair or clothes, then they will bleach. If you're out in the summer sun, there's oxygen in the air and sunlight, so your hairs go blond. Adding lemon juice to your hair means that you are adding an acid, and that just speeds up the bleaching process.

We couldn't answer this question last week, but I'm pleased to tell you that Jose Fernandez in Mexico City has been listening to us on the internet. He says that the name comes from the Spanish word 'chile', which has its own roots respectively in the Nahuatl language (the Aztecs spoke a variant of this). So a chilli was originally called chile in Nahuatl. The Spanish then took this into their own language and the English language borrowed it from them. So the fact it is called a chilli has nothing to do with its temperature at all - it's just the word that was originally used for it in another language.

It's certainly shrinking because it's giving off matter into space all the time. It's known as the solar wind. But this is a tiny fraction of the mass of the Sun and it's certainly not going to evaporate off into space before it's used up all the fuel. One statistic I did hear is that it sheds one million tonnes per second. The numbers are so big that it's difficult to equate what they are, but it's the equivalent of the mass of a reasonable sized mountain per day.

We've come a long way with this science recently. The reason for this is that the Sun has a magnetic field and the magnetic field goes out into space in the solar wind. That affects planets with a magnetic field. If you put two magnets together they will either repel or attract depending on whether they are the same or opposite. If the Sun's field in space is the opposite sign, those two fields can join together and some of this very hot gas can fall into the Earth's atmosphere. This is what is known as a geomagnetic storm. If you are measuring the Earth's magnetic field from the ground you start to see your compass needle get a bit confused because the magnetic field of the Earth is being moved about and altered by being connected to the Sun's magnetic field.

Well let's start with cold fusion. This was reported fifteen or more years ago as an interesting product where you didn't need big magnetic fields but you had electric currents passed into liquids. Somehow they suddenly gave energy off. Whether this is really fusion or whether this is just one of those funny things about electricity, I don't think has been fully demonstrated yet. But if you want to go to the more general idea of fusion as it is on the Sun, I think you have to say that on Earth we've been able to demonstrate fusion for a few fractions a second, a few milliseconds. We've never got electricity out of it; we've always put a lot of electricity into it and I think it's a very challenging thing that we haven't cracked.

The reason for that is that the shadow you're seeing is the edge of the Earth and so because one isn't completely in line with the other, you don't see the whole disk. The moon is 240 000 km away and from your vantage point you can just peer round to the dark side. We're sat on the sunward side of the planet and if you look across at a planet that's more or less the same distance from you, you can just peek around the dark side of it.

This is a really interesting debate. There are some people in the media who are saying that we need to get out in the sun as much as possible. It's really difficult because being exposed to too much sun, particularly burning, really does increase your risk of developing skin cancer. We know this from research and rates of skin cancer are set to treble in the UK as a result of too much sun exposure. But we do make vitamin D in our skin when sunlight hits our skin and we can also get vitamin D in our diet. Vitamin D is very important for building healthy bones and teeth and things like that. Deficiency in vitamin D can cause rickets and there's some evidence that it may help to prevent against cancer. So it's a difficult message to try and get across. Yes, it's important to be safe and not to burn in the sun, but at the same time you should try to be sensible about it. Don't go out in the middle of the day when it's really hot, but you'll still get enough sun to keep your levels of vitamin D healthy. SAD is another point, and it causes some people to become depressed if they don't get enough natural bright sunlight. It's not the same as not getting enough vitamin D or over exposure to the sun. It's a slightly different phenomenon.

The light that comes from the Sun would be in a continuous spectrum and it's dictated by the temperature of the Sun. The colour tells you what temperature it is. From the Sun's photosphere, the rays of light go from x-rays through visible light all the way up to radiowaves, but they peak at around 550nm, which is red light. It peaks in the visible part of the spectrum. That would be continuous were it not for the fact that there are discrete energies that are absorbed and emitted by the different atomic species on the Sun. For example, the element helium was discovered by astronomers noticing that there was a gap in the spectrum that corresponded to an element that they previously didn't know about. So they called it helium after the Greek god Helios.

I wish it was! The total energy we get in every square metre on the surface of the Earth from the Sun is about 1kW. If we could turn all of that into electricity, that would be marvellous. But I'm afraid the laws of thermodynamics stop that. The temperature of the Sun isn't so great as to turn it all into possible work, and antennae would just pick up very faint signals like the old early radio waves when you had a crystal set and got a weak signal. I'm afraid it isn't going to be useful to turn that into practical energy to power your house.

It is indeed one of those mysteries! Light can travel through a vacuum, so it doesn't require anything to push it forward with. You can think of light as particles or photons, that can travel down to their original energies.

The Sun does move. We're orbiting our galaxy; we're on one of the spiral arms of the galaxy. We go round about every 240 million years so our whole solar system is moving. But relative to our solar system it sits at the centre of the solar system and is so massive that it controls the movement of the planets. It sets the orbits of the planets.

This is a reflex called the photic sneeze reflex and no-one's exactly sure what underlies it. We know that it's genetic and is passed on in families. About one person in four or one person in five is affected. People used to think that when you looked at the Sun, the bright light made your eyes water, the water ran down into your nose, tickled your nose and made you sneeze. This is not true because it happens too fast. What scientists think is that there's some sort of crossed wiring in the back of the brain where the size of your pupil is controlled, and that's what causes that to happen.