This is similar to a question we had a few weeks ago when we were asked why it is that when a can of fizzy drink falls out of the dispenser, it doesn't explode when you open it. Dave and I discussed it and thought that when the can falls, it tends to spin. It lands on its side with the liquid spinning in a circle inside the can rather than striking the top of the can. Because the inside of the can is very smooth, the fluid doesn't come into contact with many rough surfaces and so there is nowhere for the gas to nucleate and form tiny bubbles. What could be going on in the beer bottle is that once the bottle is open, there is no pressure inside. The gas dissolved in the beer wants to come out as bobbles. If you smash the top of the bottle with another bottle, it makes a shock wave and I think that that would be sufficient to start some nucleation inside the drink. Once you have one bubble, it provides a site for other bubbles to form on. The whole thing feeds back on itself. As the bottle has a narrow neck, as soon as you have some bubbles it fills up and suddenly doesn't have anywhere to expand to. This pushes everything out in a massive volcano.

With carbon dating we're talking about different isotopes of carbon. This basically means different forms of the element. Most of the carbon in the world is a form called carbon 12, which means that there are six neutrons and six protons in the nucleus. There is also a heavier but much rarer form of carbon called carbon 14 and that's also slightly radioactive. The fact that it is radioactive means that it will break down over time. When plants photosynthesise, they take on some of this C14 and have an amount of it in their tissues. Once they die, that carbon 14 starts to break down. If you can measure the amount of carbon 14 in that organism, you can tell how long ago it died. It's effective for about 40 000 years.

No-one knows precisely why this is, but people think that it is a form of referred pain. Referred pain means that you have damage or pain coming from somewhere in your body but you feel it somewhere else. People who have a heart attack often report feeling pain in their neck or in their left arm - not where their heart is. So in the same way as that, you've got your nervous system fooled into thinking that the pain's coming from somewhere else. What scientists think is that the nerves in the mouth that are very sensitive to cold temperature accidentally trigger the nerves supplying the front of your head. It then thinks that there's a painful stimulus coming from there, when it's actually coming from your mouth. Another possibility is that when you put very cold things into your mouth, there's a nerve reflex to do with regulating heat and blood flow through your face and head. It might be that when you put something cold onto the nerves that signal this reflex, it goes into overdrive and the blood vessels temporarily open too much because they think your head is freezing cold. In the same way that a migraine will give you that horrible throbbing headache, perhaps that's why you get that temporary pain right at the front of your head.

I have absolutely no idea! They have very sensitive permeable skins so I wonder why they would want you to touch them. Perhaps they have some parasites they want you to scratch off or something!

It's an interesting question. Not all plants are green; there are plants in the sea that are brown and red. They photosynthesise in just the same way but they use pigments that trap different wavelengths of light to get that energy. This shows that you can obviously do it with other wavelengths and it's not something specifically about green. It may just be something else about the early green sea plants that were more successful than the early red and brown sea plants that made them more successful and able to get onto land. So although they look the dominant form, the fact that they are green may not make them any better at all; it could be for some other reason.

Not that I know of as their own chloroplasts, but there are more complex multicellular animals out there that pinch the chloroplasts from plants. Quite a few examples are in the cnidarians; that's jellyfish. A little freshwater jellyfish called hydra pinches chloroplasts out of green algae and keeps them in its own gut. It lets them photosynthesise and nicks the sugars that they produce. So there are animals that trick plants out of their chloroplasts.

I don't know much about grapes but it's likely to come from the chemistry of the grape, whether that's influenced by the soil or the genetics of the grape. The taste of wine comes from things called secondary metabolites that the plants produce and use to protect themselves against predators and attract animals to eat their fruit. So it's likely that different lines have different chemicals and that gives you different flavours in the wine.

Well I have to say that it's a term I've not actually heard. But the coldest part of the night is just before the sun comes through. We've lost the daytime moisture and there's still a bit of heat in the ground, but it's just as we go through to the very early hours of the morning that we see the coldest temperatures, so about 5 or 6 o'clock. You can also get a lot of condensation and dew at that time of the morning and that's what can cause lots of these problems as well. So it's a combination of the moisture and the cold temperatures that would have caused the windscreen to freeze out.

The main reason is the thickness of the cloud. A nice light fair weather cumulus tends to be quite shallow at times but as it gets bigger and bigger we sense less light coming through the cloud, and that tends to be really dark. So you get these big areas of stratocumulus that cover the sky, not a lot of sunshine gets beneath them so there's lots of shadow beneath the cloud, which makes it appear dark.

That's very true in a certain number of cases. Water in the clouds can exist in liquid form even below temperatures of zero. This is in the form of super-cooled droplets of water. But in the very thick clouds where the cloud top temperatures can be around minus 40 degrees Celsius, most of it does start off as ice. As it falls down, the cloud base is still below zero and it falls as snow and hail. But as it falls through and begins to warm up it does melt down and we actually see it on the surface as rain.

Fast repetitive ticks, which is where they got the name from, is fish blowing tiny bubbles from this structure called a cloaca at the rear end. They release these things in pulses at a certain rate and it's believed to be like some form of communication. Communicating by fish farts - fantastic!

Not a clue! It'll be to do with what the surface is made of, I guess. I don't know the difference: different wax layers maybe?

It's all down to the kidney. Your kidneys secrete a hormone called erythropoyetin, which stimulates the bone marrow to make new blood cells. What makes the kidney do that? Well the kidney has all these chemical sensors in very tiny blood vessels and it measures how much oxygen is present in the tissue and infers from that how well the red blood cells are working. In other words, how many red blood cells there must be and how well your lungs are working. If your oxygen level drops a little bit, your kidneys assume that you haven't got enough blood and makes this hormone erythropoyetin and you make more blood cells. So that means that when you go up a mountain and the oxygen levels drop, your kidney would notice that it's not getting as much oxygen as normal and would therefore boost the amount of erythropoyetin. This makes the bone marrow make more red blood cells and solves the problem. That's why you end up with thicker, heavier and denser blood if you spend time at altitude. This is also why athletes like training at altitude because it boosts the amount of oxygen an athlete can carry.

Galaxies, of course, are not the same as individual stars. The Milky Way galaxy, for example, contains 200 billion stars and is about 150 000 light years across. This means that a star on the opposite side of the Milky Way from our own solar system has been travelling for 150 000 years before it arrives at the Earth. The next nearest galaxy to our own is the Andromeda galaxy and that's about 3 million light years away, so the light that's coming from there is already 3 million years old. So it's beneficial that some suns are very long lived - suns like our sun live for 10 billion years - so there's more than enough time for light to come from the Andromeda galaxy. But you've asked a good question because space is so vast that inevitably light that's coming to us from stars up there in the sky will actually be signs of a star that's died. One day those stars will wink out because they don't exist any more, but at the moment the light is still coming to us because there's a bit of a delay. So there will inevitably be some stars but I doubt there will be a whole galaxy because they contain billions of stars and they'll all be at different phases of their lifetime.

If the Moon was low in the sky, the reason is due to an optical illusion. When the Moon is high up in the sky you've got nothing in your visual world to compare it with size-wise, so your brain attributes it to being very small. There's nothing in the foreground, you're looking at empty sky and the Moon looks very far away. But when the Moon is near the horizon, then you're seeing the Moon close or in contact with things in the foreground such as buildings, pylons, trees or even people. This fools your brain into thinking that because there's something in the foreground that it does know the size of, it compares it with the Moon and assumes that it must be much larger than it is.