When Is the Shortest and Longest Day of the Year?

The June solstice falls around 20 or 21 June and the December solstice around 21 or 22 December, everywhere on Earth. Which of them is your longest day depends on which hemisphere you are in.

That is the easy half, and it is the half every other page answers. The harder and more useful question is what those dates actually mean where you live, because the answer ranges from "barely noticeable" to "the sun does not rise".

Why the dates barely move

A solstice is a moment, not a day: the instant at which the sun reaches its greatest declination north or south. In 2026 the June solstice falls on 21 June and the December one on 21 December, in Universal Time.

The date shifts by a day here and there for two reasons. The tropical year is about 365.2422 days, so the instant drifts about six hours later each year until a leap year pulls it back. And because the instant is fixed in UT, it can fall on different local dates depending on your time zone — a solstice at 03:00 UT is still 21 June in Europe but 20 June in North America.

None of this changes which day is longest by more than a day, because near the solstice the day length is barely changing at all.

The swing is everything

Read down the table and the pattern is unmistakable. At Nairobi, a degree from the equator, the longest and shortest days differ by about nine minutes — you would never notice it without a clock. At London the difference is nearly nine hours. At Longyearbyen it is the whole year.

The reason is the same geometry that governs twilight length and golden hour. The sun's declination swings 23.4 degrees either side of the equator over a year. How much of that swing turns into a change in day length depends on the angle your horizon makes with the sun's path, which is set by your latitude.

At the equator the sun's path is nearly perpendicular to the horizon and the daily arc is close to a half-circle regardless of declination. Twelve hours, all year. Move towards a pole and the same declination change tips more and more of the arc above or below the horizon, until at the Arctic Circle it tips the whole thing.

What actually changes fastest

The day length does not change evenly. It changes fastest at the equinoxes and slowest at the solstices, following a sine curve.

In London around the equinoxes, day length changes by about four minutes a day — nearly half an hour a week, which is why late September and late March feel like the seasons are moving. Around the solstices it changes by under a minute a day, and for a fortnight either side it is effectively static.

This is what "solstice" means literally: sol plus sistere, the sun standing still. Not still in the sky, but still in its seasonal march.

That flat spot is also why the earliest sunset does not fall on the shortest day. Near the solstice the day-length effect nearly stops, and a much smaller effect — the drift between clock time and solar time — takes over and moves sunset the other way.

The solstice is not the coldest or hottest day

A common follow-on question. The longest day is in June and the warmest weather comes in July or August; the shortest is in December and the coldest weather comes in January or February.

The lag is thermal. The ground and especially the oceans take weeks to warm up and cool down, so temperature follows the accumulated energy balance rather than the instantaneous one. Peak temperature arrives when incoming and outgoing energy come back into balance, which is well after peak sunlight.

The lag is shorter inland and longer near large bodies of water, which is why coastal climates have late summers and cold springs.

The extremes

At the poles the concept breaks down entirely. The North Pole has one sunrise and one sunset a year, around the equinoxes, and the "longest day" is six months long.

Short of that, the Arctic and Antarctic Circles mark where a 24-hour day and a 24-hour night first appear. The textbook latitude is 66.5 degrees, though refraction pushes the real boundary about a degree further south.

At the other end, the equator is the only place with no seasonal variation worth measuring. Between the tropics there is a further oddity: the sun passes directly overhead twice a year, and on those two dates a vertical object casts almost no shadow at solar noon. The dates depend on latitude and are shown on every tropical city page here.

Southern hemisphere

Everything inverts, and the inversion is exact for day length. Sydney's longest day is in December, Wellington's in December, Ushuaia's in December.

One thing does not invert. The Earth is closest to the sun in early January, during the southern summer, so the southern hemisphere receives about 7 per cent more solar energy at its summer solstice than the northern hemisphere does at its own. The effect on climate is smaller than that sounds, because the southern hemisphere is mostly ocean and oceans buffer it, but it is real and it makes the southern seasonal cycle slightly more extreme in energy terms and slightly less in temperature.

Your own numbers

Every city page here shows the longest and shortest day for that city with their dates, the swing between them, and a countdown — "in four months", "two months ago". The year-overview chart plots daylight and all three twilight bands across the whole year, so you can see the shape of the curve rather than just its endpoints.

For most people the useful takeaway is the swing figure. It is the single number that says how much the seasons will actually change your daily life where you live.