No matter where you are on the globe today, the Sun will reach its southernmost apparent position with respect to our planet. This is due to the tilt of the Earth that, as the planet orbits the Sun, makes our star look like it goes up and down between the two tropics. And today, December 21, it will reach the Tropic of Capricorn.

This event happens at a very specific time: 9:27 pm CST, or 10:27 pm EST (or tomorrow, December 22, at 3:27 am UTC/GMT). This marks the astronomical changing of the season. In the Northern Hemisphere, it will be the beginning of winter, and in the Southern Hemisphere, they are entering summer. In Edinburgh, the capital of Scotland, people will get fewer than seven hours of daylight, with the Sun setting at 3:39 pm local time. The North Pole has not seen a sunrise since October, and won’t for a few more months.

The term "solstice" comes from Latin and is translated as "the Sun is still" or "the Sun has stopped". Given that the Sun appears to reach the highest or lowest point in the sky, astronomers have likened that to the motion of a ball thrown in the air, which appears to no longer move when it reaches its maximum altitude, and then starts again. 

As the Sun moves across the sky over a full year, it creates a special figure of eight shape known as an analemma.

An earlier version of this article was published in December 2022.