Is is possible to climb up the pyramids in Egypt? Yes, you can. But officials say the climb can be hazardous. The Great Pyramid of Cheops, built around 4,700 years ago, is the biggest pyramid in the world at 147 metres high. It is also one of the Seven Wonders of the World. It wasn't always possible to climb the pyramids - the pharaohs would probably have taken a very dim view of attempts to climb their royal tombs. Also, the stepped sides of the ancient tombs were once smooth - the 'steps' were originally filled in with shaped blocks of limestone. The year 2000 will be a leap year but some of the other 'century' years were not. Why? The Earth orbits the sun every 365.2425 days (approximately 365 days, five hours, 48 minutes and 45 seconds). Thus, when we add a day to every year divisible by four (leap year) to correct the calendar, we're adding a bit more time than is necessary - about 45 minutes. If this extra time was allowed to build up, it would eventually put the calendar out of pace with the seasons. The Gregorian calendar - the one we use - takes care of this extra time by dispensing with a leap day (February 29) in century years that are not divisible by 400. So the years 1700, 1800 and 1900 were not leap years even though they were divisible by four. On the other hand, 2000 will be a leap year, as was 1600. How do we prevent pimples from forming and how do we treat them? KELLY Holy Trinity College The medical term for pimples is acne. It is a skin disorder caused by excessive secretion and blocking of the sebaceous glands. These glands are associated with hair follicles and help keep the skin supple. They are stimulated by sex hormones and tend to react excessively at puberty. The condition usually settles down in early adult life. There are no specific ways to prevent pimples from forming, although it helps to keep your face clean, have enough sleep and eat a lot of fruit and vegetables. Staying away from fried foods such as potato crisps and spring rolls also helps. Acne can be treated by seeing a dermatologist. There are some acne medications that you can get from drugstores. Using medicated soap also helps. In cases of severe acne it's best to consult a doctor. How do flashlight fish produce their light? Flashlight fish emit the brightest light made by any living creature. Experts think flashlight fish use their flashlights to keep in touch with the rest of the shoal at night. The light is created by bacteria in a pouch under the eye, and can be 'switched off' by a flap of skin that covers the pouch. The fish may also use its lights to confuse predators and lure prey. Flashlight fish usually live in crevices in coral reefs and feed on small marine animals in surface waters. Their scientific name is photoblepharon palpebrates and they can grow up to nine centimetres long.