Astronomical winter begins this week for the northern hemisphere, with the winter solstice taking place on 21 December. This is the shortest day of the year, and therefore the longest night. It has been greeted with many cultural celebrations through the ages. Ancient Rome’s Saturnalia, for example, involved a week of feasting and gift-giving in which the masters served their slaves.
The winter solstice marks the moment when Earth’s north pole is tilted as far away from the sun as possible. This means that the sun appears at its most southerly position in the sky, and rises only to its lowest noon altitude, as seen from the northern hemisphere.
In the southern hemisphere, the situation is reversed. The south pole is tilted as close to the sun as possible, and people there experience their summer solstice with the longest day and shortest night.
Although the winter solstice is used to mark the beginning of astronomical winter, meteorological or calendrical winter is said to begin on 1 December.
The good news for those in the north is that from this moment onward, the sun will become progressively higher at noon, and so the length of the days will start to increase.
