In this article6 sections
By December, many of us go to work in the dark and come home in the dark. In London the Sun is up for less than eight hours on the shortest day; in Reykjavík, about four. Yet near the equator, in Singapore or Nairobi, days last roughly 12 hours all year round.
The reason is a simple fact about our planet: it leans.
It isn’t about distance
A common guess is that winter happens when Earth is further from the Sun. It’s a reasonable idea, but it’s wrong. Earth’s orbit is almost circular, and we are actually closest to the Sun in early January, about five million kilometres closer than in early July. If distance were the cause, the whole planet would have winter at the same time. Instead, when it’s winter in London, it’s summer in Sydney.
The tilt that makes the seasons
Earth spins around an imaginary line through the North and South Poles, called its axis. That axis isn’t upright compared with Earth’s path around the Sun. It is tilted by about 23.4 degrees, and it keeps pointing in the same direction in space all year.
So as Earth travels around the Sun:
- For part of the year, the northern hemisphere leans towards the Sun. The Sun climbs high in the sky, takes a long path from sunrise to sunset, and days are long. That’s the northern summer.
- Six months later, the northern hemisphere leans away. The Sun stays low, takes a short path across the sky, and days are short. That’s the northern winter.
The southern hemisphere gets the opposite, which is why Australians and South Africans celebrate Christmas in summer.
Earth is closest to the Sun in early January. Winter is about tilt, not distance.
Why low sun means cold, too
Shorter days mean fewer hours of sunshine to warm the ground. But the low angle matters just as much. When the Sun is low, its light hits the ground at a slant and is spread over a larger area, like a torch beam shone at an angle, so each square metre receives less energy. The light also passes through more atmosphere on the way. That’s why the winter sun can feel weak even on a clear day, and why cold air can sit trapped near the ground for days in some cities.
The winter solstice
The day when your hemisphere leans furthest from the Sun is the winter solstice, the shortest day of the year. In the northern hemisphere it falls on 21 or 22 December. In 2026 the exact moment is on 21 December at 20:50 UTC, which is already 22 December in eastern Asia, Australia and New Zealand.
After the solstice, days start getting longer again, slowly at first and then faster, until the summer solstice in June.
How short the shortest day is depends on how far you are from the equator:
| Place | Daylight on the December solstice, roughly |
|---|---|
| Singapore (near the equator) | 12 hours |
| New York | 9 hours 15 minutes |
| London | 7 hours 50 minutes |
| Edinburgh | 7 hours |
| Reykjavík | 4 hours |
| Sydney (southern summer) | 14 hours 25 minutes |
North of the Arctic Circle, the Sun doesn’t rise at all for a period around the solstice. In Tromsø, in northern Norway, this polar night lasts from late November to mid-January.
Why the earliest sunset isn’t on the shortest day
If you live in Europe or North America, you may have noticed something odd: evenings start getting lighter before Christmas, yet mornings keep getting darker into January.
In London, the earliest sunset is around 12 December, about a week before the solstice, and the latest sunrise is around the end of December or early January. The shortest day still falls on the solstice; it’s just that the darkest evening and the darkest morning don’t line up with it.
The reason is that a “day” measured by the Sun isn’t always exactly 24 hours. Because Earth’s orbit is slightly oval and its axis is tilted, the time from one solar noon to the next varies a little through the year, and in December it’s about 30 seconds longer than 24 hours. Our clocks ignore this and use an average day. So around the solstice, solar noon drifts slightly later each day by the clock, which pushes both sunrise and sunset later. Sunset starts getting later before the solstice; sunrise keeps getting later after it.
Why the coldest weather comes later
If the solstice gets the least sunshine, why is January usually colder than December? Because land and, especially, the oceans store heat. Through autumn and early winter they keep losing more heat than the weak sun puts back, so temperatures keep falling for weeks after the shortest day. This delay is called seasonal lag. In much of the northern hemisphere, the coldest weather typically comes in January or February.
Frequently asked questions
Do the clocks going back make the days shorter?
No. Changing the clocks in autumn doesn’t change how much daylight there is; it only moves it. After the change, sunrise and sunset both come an hour earlier by the clock, so mornings are lighter and evenings darker.
Is the winter solstice always on 21 December?
Not always. Because a year is about 365 and a quarter days long, the exact moment shifts a little each year. In the northern hemisphere, the December solstice falls on 21 or 22 December, depending on the year and your time zone.
Can short winter days affect how I feel?
Many people feel more tired or low in winter, and for some this is part of seasonal affective disorder (SAD), which is linked to reduced daylight. Getting outside in daylight, especially in the morning, can help. If low mood is affecting your daily life, talk to a doctor.