Not a mistake, but astronomy Earliest sunset - why it was yesterday and not on December 21

The sun is already setting earlier than ever before - even though the shortest day of the year is still to come. Many people think this is a mistake. But there is simple astronomy behind it.

Yesterday, blue News reported that the sun set earlier on Thursday than on any other day of the year. This caused astonishment among some readers.

Several emailed to ask whether the earliest sunset should not occur on December 21, the day of the winter solstice. After all, this is the shortest day of the year. The suspicion of a mistake is obvious - but it is unfounded.

In fact, the shortest day and the earliest sunset do not fall on the same date. In Zurich, the sun disappeared behind the horizon at 4.35 pm on Thursday. From Friday onwards, sunset slowly shifts back again.

The situation is different in the morning: sunrise will continue to be later until the turn of the year. In Zurich, it reaches its latest time on January 1 at 08.13 a.m., as data from "MeteoNews" shows.

Earth's movement is not perfect

The reason for this shift lies in the movement of the Earth. It does not orbit the sun in a perfectly circular path, but in a slightly elliptical one. As a result, its speed changes over the course of the year. From our perspective, the sun therefore does not always move evenly across the sky.

Added to this is the tilt of the Earth's axis. This means that the highest position of the sun - known as true noon - is not reached at the same time every day. Experts refer to the difference between this solar time and our time as the equation of time. These effects are particularly pronounced in December.

The result is an apparent contradiction: although the days continue to get shorter until the winter solstice on December 21, the later sunset occurs earlier. The earliest sunset in mid-December is therefore not an error, but a well-explained result of celestial mechanics.

Incidentally, the winter solstice does not fall on exactly the same date every year either. The reason for this is also the uneven movement of the earth around the sun. The solstice is usually on December 21. In 2025, it actually occurs on this day, at 4.03 pm. This is when the sun reaches its lowest midday height above the horizon. In other years, however, this time may be delayed. In 2027, for example, the winter solstice will not fall until December 22.