Weather AddictBy Steff GaulterHave you noticed how short the days are now? I’m now leaving work in the dark. As humans aren’t generally nocturnal creatures, you’ll probably be pleased to hear that we’ve now passed the worst of it. Friday, December 21, was the shortest day of the year, and actually, if you believe the Mayan calendar, the same time that the world was supposed to end. However, given that we’re now two days after the doomsday scare, I think we can safely say we dodged that one. Anyway, end of the world aside, the shortest day is also called the winter solstice, the point when the sun reaches its southern-most point over the earth.We all know that earth rotates and that’s why we have day and night. During the daytime we’re on the side of the earth that faces the sun, and at night we’re around the other side, facing away from it. If the story ended here, then we would all have about 12 hours of sunshine and 12 hours of darkness, but when was anything ever that simple?As well as rotating on its own, the earth also rotates around the sun. It takes 365.25 days to go all the way around the sun. In the Western Gregorian calendar we have 365 days in a year, a quarter of a day shorter than it should be. If we just ignored this quarter of a day, then eventually the northern hemisphere’s summer would end up in February and things would get terribly confusing.Julius Caesar is credited with creating an extra day in February every fourth year to keep the seasons at the correct time of year. At that time the Romans had a 355 day calendar, with an extra month inserted every other year. Julius Caesar decided to simplify things, making each year 365 days, with one extra day in February every fourth year.Actually it’s not quite true to say that every fourth year is a leap year. A year is just slightly less than 365.25 days, so adding an extra day every four years results in about three days too many over a period of 400 years. For this reason, only one out of every four century years is considered as a leap year. Therefore although the year 2000 was a leap year, the year 2100 won’t be. It’s just a shame that I won’t be around in 2100 in order to impress people with my knowledge!As well as rotating in a way that is slightly unhelpful as far as our calendars are concerned, the earth also rotates at an angle. The North Pole isn’t at right angles to the sun, it’s slanted at an angle. As the earth goes around the sun, sometimes the northern hemisphere is angled towards the sun and at other times it’s pointing away from it.On the earth we notice this tilt by the fact that the sun isn’t always overhead at the same point. At the height of the northern hemisphere summer, when the northern hemisphere slants towards the sun, the sun is directly over the Tropic of Cancer, overhead in southern Taiwan, the Bahamas in the Caribbean and Muscat in Oman.The other extreme is the height of the northern hemisphere winter, when the northern hemisphere slants away from the sun. At this point the sun is blazing over the Tropic of Capricorn in the southern hemisphere, directly over Rockhampton, to the north of Brisbane in Australia, southern Madagascar and Rio de Janeiro in Brazil.This was the position of the sun on December 21, directly over the Tropic of Capricorn. If you strictly follow the planets, then this was when the summer started in the southern hemisphere and winter started in the northern hemisphere — a little late as far as many people buried in snow in Europe, Northern America and northern Asia would say! The meteorological offices in the northern hemisphere normally state that winter is December, January and February. This is when the coldest weather is and it also helps to avoids confusion, as the winter solstice moves slightly every year.Whenever you believe that winter starts, the winter solstice is always the shortest day of the year. This is the time that the North Pole is slanting away from the sun and the most northern parts of the globe will endure 24 hours of darkness.Of course here in Qatar it’s not dark for 24 hours, but the days are definitely shorter. On the longest day of the year, June 21, the day was 13 hours 43 minutes long. Six months later, on December 21, the day had shrunk to just 10 hours 34 minutes long, a difference of 3 hours 9 minutes. Although most of us are now driving back from work in darkness, at least the journey to work will be in the sunshine. Not everywhere is so lucky.On the shortest day of the year Vancouver receives 8 hours 10 minutes of daylight. Further north in Stockholm, there’s even less: 6 hours, 4 minutes. People in these cities and many others will travel both to and from work in pitch darkness which can significantly affect people’s mood. It has been found that lack of sunlight can cause people to sleep too much, suffer a lack of energy and feel seriously depressed. The condition, known as Seasonal Affective Disorder (SAD), is thought to affect nearly 10% of those people living in the northeast US State of New Hampshire.Before you laugh at the thought of someone suffering from SAD in Qatar, you might be interested to hear that even in the sunshine state of Florida 1.4% of the population is affected. If you feel like hibernating over the next few months, there could well be a good reason why. At least the cooler, shorter days in Qatar are short-lived.(The author is Senior Weather Presenter at Al Jazeera English channel. She can be contacted on steff.gaulter@yahoo.co.uk or on Twitter at @WeatherSteff)