Why the earliest sunset is not on the shortest day

Every December the same question comes up: if 21 December is the shortest day, why do the evenings already start getting lighter around the middle of the month? And why are the mornings still getting darker into January? The answer is that sunrise and sunset do not move symmetrically around the solstice. Solar noon itself is drifting later through the clock day.

The numbers

Here are the sunrise and sunset times in Ljubljana around the winter solstice. Look at the sunset column: it reaches its earliest time well before 21 December. The sunrise column keeps getting later until early January.

Date	Civil dawn	Sunrise	Solar noon	Sunset	Day length
Dec 1, 2026	06:49	07:23	11:51	16:18	8 h 55 min
Dec 7, 2026	06:56	07:30	11:53	16:17	8 h 47 min
Dec 11, 2026	06:59	07:34	11:55	16:16	8 h 43 min
Dec 15, 2026	07:03	07:37	11:57	16:17	8 h 40 min
Dec 21, 2026	07:06	07:41	12:00	16:19	8 h 38 min
Dec 27, 2026	07:09	07:43	12:03	16:23	8 h 39 min
Jan 3, 2027	07:10	07:44	12:06	16:29	8 h 45 min
Jan 10, 2027	07:09	07:43	12:09	16:36	8 h 54 min

The day length (the last column) is shortest on the solstice, exactly as expected. But the whole “block” of daylight is sliding later in the clock day at the same time.

Why solar noon drifts: the equation of time

Clocks assume that the sun passes the meridian (its highest point) at the same time every day. The real sun does not keep such perfect time. Over the year it runs up to about 16 minutes fast and up to about 14 minutes slow compared with an imaginary “mean sun” moving at a constant pace. That difference is called the equation of time.

It has two causes:

1. Earth’s orbit is an ellipse. Earth is closest to the sun in early January and moves fastest then. The faster Earth moves along its orbit, the further it has to turn to bring the sun back to the meridian, so the solar day is slightly longer than 24 hours in December and January.
2. Earth’s axis is tilted. Even on a circular orbit, the sun’s apparent motion along the ecliptic projects onto the equator unevenly. Near the solstices the sun moves more “sideways”, which also lengthens the solar day.

In December both effects add up. Each solar day is about 30 seconds longer than 24 hours, so solar noon moves about 30 seconds later every day. Over the three weeks around the solstice that adds up to more than 10 minutes.

Putting it together

Imagine the daylight as a block centred on solar noon. Around the solstice the block is shrinking at only a few seconds per day, because day length changes slowly near its minimum. At the same time, the whole block slides later by about 30 seconds per day.

• Sunset is at the end of the block. Before the solstice it is being pulled earlier by the shrinking day, but the sliding pushes it later. About ten days before the solstice the sliding wins, and sunsets start getting later again.
• Sunrise is at the start of the block. Shrinking and sliding both push it later until the solstice. After the solstice the day starts growing, but only slowly at first, so the sliding keeps pushing sunrise later until early January.

Explore it yourself

The solar noon calculator shows the equation of time and how solar noon drifts through the year for your location. The day length chart shows sunrise and sunset as curves, where you can see that the lowest point of the sunset curve and the highest point of the sunrise curve do not line up with the solstice. Every city page also lists the dates of the earliest sunset and latest sunrise.