Starwatch: shortest day in reach as astronomical winter begins

Winter solstice marks moment when Earth's north pole is tilted as far away from the sun as possible

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.