How day length changes with latitude: from 12 hours to 21

November 3, 2026 · 5 min read

Everyone knows that winter days are short and summer days long. What surprises people is how little that is true near the equator and how extreme it becomes in the north. The difference comes down to one number: latitude.

Calculated day lengths

From sunrise to sunset, with the standard rule (upper edge of the sun, standard refraction), at the December solstice 2026 and the June solstice 2027:

Why the equator stays near 12 hours

The Earth’s axis is tilted about 23.4°. At the equator, whatever the season, the line between day and night cuts the circle of latitude exactly in half, so every point spends about half of each rotation in daylight. The few extra minutes come from refraction and from defining sunrise by the sun’s upper edge, which together add a little daylight at both ends of every day, everywhere.

Why the north swings so much

Away from the equator, the tilt means the circle of latitude is cut unequally. In June the Northern Hemisphere is tilted toward the sun, so more than half of each northern latitude circle is lit; in December, less than half. The further from the equator, the more unequal the cut. Beyond the Arctic Circle, at about 66.6° N, some summer days are entirely light and some winter days entirely dark.

Refraction matters more in the north

Near the poles the sun crosses the horizon at a shallow angle. The roughly half-degree lift from refraction then shifts sunrise and sunset by many minutes, not two or three. This is why Reykjavik’s summer day is longer than simple geometry suggests, and why the exact rule used for sunrise matters more in Tromsø than in Singapore.

The equinoxes are not exactly equal

At the March and September equinoxes, day and night are often said to be equal everywhere. Because of refraction and the upper-edge definition, the day is actually a few minutes longer than 12 hours on the equinox; the date of truly equal day and night, sometimes called the equilux, comes a few days before the March equinox and a few days after the September one at mid-latitudes.

How fast the days change

Day length changes fastest around the equinoxes and slowest around the solstices, and the rate grows with latitude. Calculated for the March equinox of 2027, the day lengthens by about 6.5 minutes a day in Reykjavík, 3.6 minutes a day in Paris and only about 6 seconds a day in Singapore. Over a month in spring, Reykjavík gains more than three hours of daylight; Singapore gains a few minutes. That is why the change of season is felt so strongly in the north: the evenings visibly stretch from one week to the next.

The southern hemisphere, mirrored

South of the equator the seasons are reversed and the same rules apply. At Ushuaia, in Argentine Tierra del Fuego at about 54.8° south, the day lasts about 17 hours 20 minutes on 21 December 2026 and about 7 hours 13 minutes on 21 June 2027. At Hobart, in Tasmania, the figures are about 15 hours 21 minutes and 9 hours 1 minute. There is far less land at high southern latitudes than in the north, so very few people experience the southern extremes; the Antarctic stations are the exception.

The equilux, calculated

For Paris in 2027, the day closest to exactly 12 hours from sunrise to sunset comes on 18 March, two days before the equinox of 20 March, and on 26 September, three days after the equinox of 23 September. On the equinox days themselves the Paris day is several minutes longer than 12 hours. The offset comes from the definition: sunrise is counted from the first glimpse of the sun’s upper edge, lifted by refraction, so every day gains a few minutes of “extra” daylight at each end.

A surprise: the total over a year

Short winter days and long summer days might be expected to cancel out exactly. They nearly do, but not quite. Adding up the hours when the sun’s upper edge is above an ideal horizon over the whole of 2027 gives about 4,429 hours at Quito, 4,476 at Paris, 4,578 at Reykjavík and 4,605 at Tromsø, against 8,760 hours in the year. Everywhere receives slightly more than half the year in daylight, thanks to refraction and the size of the sun’s disc, and the gain grows toward the poles, where the sun spends a long time just at the horizon. Over a year, Tromsø, with its weeks of polar night, sees the sun for more hours than the equator.

That is a statement about hours, not about warmth or brightness. At high latitudes the sun is low for much of that time and its light is spread thinly; the equator receives far more energy from the sun even with fewer hours of it.

Choosing a moment anywhere

These differences shape any gift tied to the sun. A sunset in Reykjavik in June happens close to midnight; a sunrise in Paris in December after 08:30. You can pin any place and see the exact time of The Sunrise or The Sunset before you choose.