Year’s shortest season starts at December solstice

Year's shortest season: Low red horizontal streaks below deep blue sky, behind a bare tree.
View at EarthSky Community Photos. | Karl Diefenderfer of Quakertown, Pennsylvania, wrote: “Vibrant winter’s solstice sunrise.” Thank you, Karl! By the way, the December solstice starts the year’s shortest season.

The year’s shortest season has begun

Did you know that Earth’s seasons are slightly different lengths? And by season, we mean the time between a solstice and an equinox. The current season – between the December solstice and March equinox – is a touch shy of 89 days. So it’s Earth’s shortest season.

Here are the lengths of the astronomical seasons:

December solstice to March equinox: 88.99 days
March equinox to June solstice: 92.76 days
June solstice to September equinox: 93.65 days
September equinox to December solstice: 89.84 days

The December solstice occurs when the sun reaches its southernmost point in our sky for this year. That is what’s happening this week, at 3:27 UTC on December 22, 2023 (9:27 p.m. December 21 CST). This solstice marks an unofficial beginning of the winter season in the Northern Hemisphere, and the start of the summer season in the Southern Hemisphere. Unofficial? What? That’s correct. While no government body has decreed it shall be so, we all generally agree that the solstices and equinoxes are hallmarks of seasonal change.

Check out the 2024 EarthSky lunar calendar. A unique and beautiful poster-sized calendar showing phases of the moon every night of the year. It makes a great New Years gift.

So no matter where you are on Earth, the current season – between the December solstice and March equinox – marks the beginning of your shortest season.

Contrast the number of days in the present season with that of Earth’s longest season – the time between the June solstice and September equinox – in other words, a Northern Hemisphere summer or Southern Hemisphere winter. Because that is Earth’s longest season and lasts 93.65 days.

But the current season is nearly five days shorter. Why?

The reason for the shortest season

As a matter of fact, every year in early January, the Earth swings closest to the sun for the year. And this nearest point is called Earth’s perihelion. Because Earth reaches perihelion in early January, our planet moves most swiftly in its orbit around now. That is just physics: Planets move faster when they are closer to the sun than when they are farther from the sun. And it’s why a Northern Hemisphere winter, or Southern Hemisphere summer, is the shortest of the four seasons. It simply takes us fewer days at this time of year to move between a solstice and an equinox.

On the other hand, in early July, Earth is at aphelion – or farthest from the sun – and moving most slowly in its orbit. So that’s why the longest season occurs at that time.

But of course, seasons change

According to the computational wizard Jean Meeus, a Northern Hemisphere winter or Southern Hemisphere summer became the shortest season after the year 1246. The astronomical season between the December solstice and the March equinox will reach a minimum value of 88.71 days around the year 3500, and will continue to reign as the shortest season until about the year 6430.

Crescent Earth, with the dark side illuminated by strings and nodes of yellow lights.
The lights of cities from the nightside of Earth. This composite image of Asia and Australia at night used data from the Suomi NPP satellite. Image via NASA.

Bottom line: Earth’s shortest season begins at the solstice on December 21-22, 2023. The coming season – Northern Hemisphere winter or Southern Hemisphere summer – is a touch shy of 89 days in length.

Read more: All you need to know about 2023’s December solstice

December 21, 2023

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