Winter Solstice: Why December 21 has longest night of the year

December 21

December 21 (or sometimes December 22) is indeed the day with the longest night of the year in the Northern Hemisphere.

Science behind this

The reason lies in Earths tilt and its annual orbit around the Sun.

Earth’s tilted angle

Earths axis is tilted at an angle of 23.5° relative to the plane of its orbit. This tilt isnt uniform throughout the year, and on December 21, the North Pole is tilted farthest away from the Sun.

Least amount of Sunlight

As a result, the Northern Hemisphere receives the least amount of direct sunlight on this day. The Sun appears lower in the sky, traveling along a shorter path, and sets earlier in the day.

Longest night of the year

This translates to fewer hours of daylight and, consequently, the longest night of the year. Conversely, the Southern Hemisphere experiences the exact opposite – the summer solstice with the longest day and shortest night.

Date & Time

The exact timing of the winter solstice can vary slightly from year to year. In 2023, it falls on December 21 at 15:28 UTC.

Celebrations around the world

The winter solstice marks the astronomical beginning of winter in the Northern Hemisphere and summer in the Southern Hemisphere. Many cultures around the world have traditions and celebrations associated with the winter solstice, recognising the return of sunlight and the promise of longer days to come.