Today, 21 December at 22:03 GMT the North Pole (with the earth’s axis at 23.5 degrees) tilts its furthest away from the sun. This is the shortest solar day of the year and we call it the winter solstice.
For thousands of years, people in the Northern hemisphere have noticed it and celebrated. The pagan festival of Yule marks the rebirth of the sun and start of winter on the solstice. Druids would sacrifice animals under the sacred plant mistletoe as part of their Yule rituals.
The Romans held the week-long Saturnalia at this time and decorated their homes with holly wreaths to ward off evil spirits.
Christmas was established in late December in the fourth century, deliberately to override the attraction of the pagan festivals.
Another curious thing is that although you’d expect the shortest day of the year to have the latest sunrise and the earliest sunset, this isn’t the case. The latest sunrise does not occur until around the 2nd of January and the earliest sunset has already happened – around the 10th of December.
However, after the solstice each day is getting lighter every day. This is because solar days in December last around 24 hours and 30 seconds, while we still measure each day as exactly 24 hours. Because of this, the sun cycle on each day is about 30 seconds later every day, until the solar days shorten again. It’s hard to notice it at first, as to start with it is only by seconds a day but soon a minute, then 2 minutes a day. However, the evenings are getting lighter again as we set the course for summer!
In Edinburgh, today is 10 hours, 39 minutes shorter than on the June summer solstice.
Next year winter solstice will be on 22nd December at 04:38 am.