Is the earliest sunset on the winter solstice?

Day length is the time from sunrise to sunset, and on the solstice it is the shortest of the year. But a shorter day does not mean sunrise and sunset shrink evenly from both ends.

In December, solar noon, the moment the sun stands highest in the southern sky, arrives a little later each day. So the whole stretch of daylight slides toward the afternoon on the clock. Just before the solstice, this shift is larger than the daily loss of daylight, so sunset times have already started getting later again.

Our clocks always measure a day as exactly 24 hours. But the time it takes the sun to return to its highest point in the southern sky is not the same all year.

Earth orbits the sun not in a perfect circle but in a slightly squashed ellipse, and it moves faster in early January when it is closest to the sun. On top of that, Earth's axis is tilted, so the direction the sun travels across the sky changes with the seasons. In December these two effects add up, making the sun's day about 30 seconds longer than 24 hours, and over a few weeks that difference adds up to more than ten minutes.

The saying that evenings get longer right after the solstice is only half true. Evenings have been stretching slightly since early December, while mornings keep getting darker until early January. That is why the darkest morning commute is not on the solstice but around the first week of the new year.

To check for yourself, look up sunrise and sunset times by date and region on the Korea Astronomy and Space Science Institute website. In Seoul, sunset is earliest in early December at around 5:14 p.m., and around the solstice it is about 5:17 p.m. The feeling that the sky on your way home gets a tiny bit brighter from mid-December is not your imagination.