When light from the sun shines into a raincloud, it hits a raindrop, goes inside the raindrop, reflects off the opposite inside surface of the raindrop, and then leaves from the front again. Just as in a prism, as the light leaves the raindrop it is split up into its constituent colours of the spectrum, producing the first rainbow you see. But sometimes when the light is very bright and the sky very dark you can see a second rainbow outside the first one and if you look very closely you'll see this is in fact a mirror image of the first rainbow. The reason for this is that after it has bounced off the back of a raindrop, some light is reflected back off the front of the raindrop again and repeats the whole process, completing the journey twice. As a result, when it finally leaves the front of the raindrop it emerges at a different angle and as a mirror image, producing a second rainbow outside the first.

Yes, but to a lesser extent than the moon, which is the main determinant of our tides. You can work out if we are on a neap tide or a spring tide - that's a high tide or a low tide - depending on whether these two celestial bodies line up with each other. When the sun is in alighnment with the moon we have a new moon (which means you can't see it because it is not illuminated and is dark) and the two bodies work together gravitationally, producing a spring tide. Two weeks later, however, the moon is at 90 degrees to the sun, so they're not in alignment, so you have a neap tide. Two weeks after that you have a full moon and the two are working together again, and you have a spring tide.

You are lucky to have had it diagnosed because lots of people with it and are undiagnosed. People who have apnoea stop breathing, maybe hundreds of times a night, which means that your brain is regularly starved of oxygen producing symptoms of tiredness, poor concetration and irritability the next day. There is a way of treating this and that is to wear a mask which pushes air down into the lungs under pressure - maybe your doctors have told you about this - but you'd need to use this every night for life. There are two possibilities for what causes sleep apnoea: central apnoea is where the bit of the brain which tells you to breathe whilst you're asleep switches off - but this is rare. More common are problems in the throat so when you fall asleep your muscle tone goes away and your throat collapses, obstructing the airway. This is why pushing air down with a mask can help. People who have this can have surgery to correct it, but the surgery is fairly major.

This could be that you have a small viral infection of the eyes and a bad back, or there is a disorder called Ankylosing spondylitis, which is caused by the immune system attacking the body itself. This is a progressive back condition which can have dry eyes associated with it, although not usually a sudden onset as in your case. There is a blood test that can help to confirm this, so it is best to go and see your GP and discuss this possibility.

Surveys have shown that about 6% of the population say that they absolutely never dream. There doesn't seem to that much difference between them and the rest of the population, but what has also been done is take some of these people and wake them up in sleep lab when they're in REM sleep. Every 90 minutes or so during your sleep the majority of people go into REM sleep, so you put these people in the lab, wire them up, and what happens is that you can wake people up during these periods of sleep when they ought to be dreaming. With most people you've got about an 80% chance of a dream being reported if you wake them up like this. Now if you're a non-reporter of dreams, that is one of the 6%, what's been found is that 0.6% of these absolutely never report a dream even if you wake them up during REM sleep, so in your case Betty, it is quite possible that you are having dreams and you just don't remember them.

We don't know about this, but they should! Tube drivers for instance don't get much daylight so this is bound to have an impact on your biorhythms. Night shift workers tend to be more accident prone, and the sleepier you are the more likely you are to be overconfident. There have been studies that show that for nurses in the US, there was a 20% greater incidence of breast cancer which may be due to the cortisol they're producing.

Narcolepsy is the disorder where people fall asleep repeatedly during the day and there seems to be genetic component to this. Luckily there are drugs which can be used to treat it. There can be frightening aspects to narcolepsy, for instance people have been known to suddenly fall down as they fall asleep, or have nasty hallucinations as they fall asleep. The brain chemistry behind it is better understood now, and we do know about the genes that are linked to this. One particular chemical is a substance called hypocretin, and people with narcolepsy tend to have problems with the receptors for this brain chemical, or an abnormal form of this chemical. There are also people with 'clock' genes that give them a faster or slower body clock, but this shouldn't be mistaken for narcolepsy.

Viral infection can affect your brain, and body clock, which may be the cause here. The body clock is in the part of the brain called the hypothalamus, so infection and high body temperature around this area could affect your body clock. In your case though, it seems that your body clock does work, it's just maintaining it that is the problem.

Lucky man ! This is to do with the amount of sleep that people get in the first place. Deep sleep and REM sleep is the key. The more people get of this the less sleep they need, which is why people sometimes say they only need 4 or 5 hours sleep rather than the standard 8 hours.