It's a bit of both, because there are two things going on here. The skin on your eyelids has a very rich blood supply and is also very thin, which allows some light to pass through. Blood looks red because of the iron in haemoglobin, which absorbs all colours of light except red (which it reflects). Some of that red light is reflected out of the blood in your eyelid and into your eye, which therefore accounts for some of the red you can see. The second part of the tale is that tissue transmits red wavelengths of light very well, but it doesn't transmit blue or wavelengths of light towards the blue end of the spectrum very well. So what happens is that light hits your eyelid, and blue light is absorbed by the skin, while the red light travels through. By the time the light travels through your shut eyelid and enters your eye, it's mainly red light that's getting into the eyeball, which is why you see red.

We've had a few answers sent in for this question. Thanks to everyone for their input!

Brian in the Costa Blanca - Yes you're pee could knock you over. I turned round once and hit someone with my stream and the guy fell over!

Andrew in Brighton - If you're on a travelator that started with a bang or stopped with a bang, you'd fall over if you're going too fast. I looked on the web and the Department of Transport say that half a metre a second is a safe speed, so with regards to the question, if suddenly somebody started up peeing or stops, you'd probably fall over. What you're after is moving someone with a jolt of half a metre a second. As Will said, it's a matter of action and reaction. I'm 85 kilograms. Now if I was going to move backwards at half a metre a second, I would have to project one kilogram of water at 42.5 metres per second. That is a 150 kilometres per hour. If you could do that then you could pee 90 metres in the air, which I would be hard pushed to do. You're talking about a fireman's hose with something like 2kW of power put into it to do anything like that height. If you run upstairs briefly if you're really fit and expend about 1 kW for a short time. That's using the large muscles of your legs, but the abdominal muscles are not designed to do that kind of work at all, so the answer is definitely not. You could not expel urine that fast.

There's still a problem with this, which is that you have to achieve what's called orbital velocity. You could get very close to space in a big airship, but if you let go you would still fall. In order to be in orbit you have to be moving fast enough that gravity is just strong enough to hold you in a circular orbit. This is about 27 000km/hr so whilst a large balloon would help you get into space, it wouldn't help with the difficult bit of moving fast enough to stay there.

Saying that some american companies are suggesting it as a way of getting into space, because if you can get up above the atmosphere, you don't need to fight air friction so a large rocket to get into space in not needed, you can gently gain height using a much smaller one for much longer.

When hair gets wet it gets closer together. Hair is light when it's dry for the same reason that glass is clear when it's as a glass but lighter when it's made into tiny particles of sand. What's happening when it's dry is that light is bouncing off all the surfaces of the hair and bouncing around all over the place and reflects lots of wavelengths of light and looks lighter. When the hairs are covered with water it smooths the surfaces, more light can go through deep into the hair rather than be reflected back, so it looks darker.

People have wondered about this for some time because it probably is deleterious to your joints. So what's going on here? Well when you put your joints under tension, what you're doing is reducing the pressure inside the joint. You get the little clicks because all the ligaments around the side of the joint that stabilise it get sucked in against the fluid in the joint. Because the pressure in the fluid is reduced, gas that's dissolved in that fluid can then come into one big bubble and pops into existence. The bubble takes up about 15% of the joint space that's there for the fluid to occupy normally. As this is something that's quite a big space in something that's full of fluid, it pushes all of the little ligaments that were pushing in inside of the joint back out again, and they go snap. That's the cracking sound that you hear. The energy that's unleashed in making and breaking that bubble is about 7% of the energy you'd need to damage cartilage, so it shouldn't in theory be able to cause arthritis. Some facts and figures though: there was a man called Daniel Unger who cracked the joints of his left hand for fifty years but not the joints of his right hand. He did not have any signs of his left hand being more arthritic than his right hand. There's been one other study, bit dicey, but there were 300 people who all cracked their joints for 35 years and there was no evidence of increased risk of arthritis among those people, but there grip strength was much weaker - only about 25% of what it should be.

Silicone is a big polymer, which is a bit like a load of spaghetti chains all linked together. It's lots of silicon surrounded by oxygens, and they form these big long chains linked up end to end. They are actually water repellent. If you lick your finger and smooth it, then what you're able to do is push it into place but it won't stick to you because your finger's got a layer of water on it and it doesn't like water. This keeps the silicone away from you and as a result you can push it into the shape you want. As for why it works with saliva and not salt water or ordinary water is that there are other clever things in saliva such as a protein called mucin, which is why your saliva's all slimy. That may also be helping to lubricate the silicone from locking onto your finger. That's the only thing I can think of. Perhaps someone else can help us with this!

What I think is going on is that the ground is looses heat by radation. So it can see the clear cold sky above it on a clear night and the ground radiates away lots of its energy very quickly and goes down to zero or below zero very effectively, because the ground is good at giving up energy. But the air and the atmosphere sitting above the ground is effectively transparent to the radiation  so it doesn't absorb or emit radiation well, so it doesn't cool down nearly as fast or insulate the ground very much.  So the air loses it's energy much more slowly than the ground does. This means that the air can be a three degrees but the ground is now lower that, say zero or even minus three degrees. So when the warm damp air meets the air, it cools down and the moisture condenses out as frost on the ground even though the air temperature is still not quite freezing.

The answer is that we just don't know, but what we do know for sure is that the universe is getting a lot larger. If you look at distant galaxies a long way from us, they are something called red shifted. What that means is the light waves coming from them to us have been stretched out. The reason they've been stretched out is because the space separating us and that distant galaxy has got bigger. So it stretched the waves and makes them more red-dominated than it should be. That's a similar reason that when a police car comes towards you, it sounds different for when it's going away from you because of something called the Doppler shift.

The atmosphere of the earth is pretty much transparent to the heat coming from the sun, which hits the surface of the earth and heats it up to about 1 kW per metre squared. This heat then gets irradiated back up into the air, warms the air close to the planet - and of course, you. But then the hot air rises, goes up into the atmosphere, expands and gets cold. That's why as you go further up in the atmosphere, things get colder.