Sunrise, Sunset and Day Length: Why They Change Through the Year
Days get shorter after the June solstice because Earth’s axis is tilted about 23.44 degrees, so for half the year the Northern Hemisphere leans away from the Sun and the Sun crosses a shorter, lower arc across your sky. How much daylight you lose depends on your latitude: in early August, Paris loses about 3 minutes a day, Oslo about 5, Singapore almost nothing.
Why day length changes
Earth spins on an axis tilted 23.44 degrees from the plane of its orbit, and that axis keeps pointing the same way in space all year. As Earth goes around the Sun, the hemisphere tipped toward the Sun gets long, high-arcing days and the other gets short, low ones. Distance has little to do with it: Earth is actually closest to the Sun in January, during the northern winter.
Astronomers describe the Sun’s position with its declination, the latitude on Earth where the Sun is directly overhead at noon. It swings between 23.44 degrees north at the June solstice and 23.44 degrees south at the December solstice, crossing the equator at the equinoxes. The higher the Sun’s declination on your side of the equator, the more of its daily circle stays above your horizon, and the longer your day.
The Southern Hemisphere gets the mirror image. Sydney has about 9 hours 54 minutes of daylight at the June solstice and about 14 hours 25 minutes at the December solstice, which is why its summer holidays fall around Christmas.
Latitude decides how much
At the equator, day length barely moves: about 12 hours 7 minutes every day of the year. The farther you go from it, the bigger the swing between June and December. The table uses the same calculation as our city pages (NOAA solar equations, standard sunrise definition, 2026 dates).
| City (latitude) | March 20 | June 21 | September 23 | December 21 |
|---|---|---|---|---|
| Singapore (1.3° N) | 12 h 6 min | 12 h 12 min | 12 h 6 min | 12 h 3 min |
| Cairo (30.1° N) | 12 h 7 min | 14 h 5 min | 12 h 7 min | 10 h 13 min |
| Paris (48.9° N) | 12 h 10 min | 16 h 11 min | 12 h 8 min | 8 h 15 min |
| Oslo (59.9° N) | 12 h 12 min | 18 h 50 min | 12 h 11 min | 5 h 54 min |
| Reykjavik (64.1° N) | 12 h 15 min | 21 h 8 min | 12 h 12 min | 4 h 7 min |
Two things stand out. First, the gap grows slowly at low latitudes and then very fast toward the poles: Cairo’s longest day is under 4 hours longer than its shortest, Oslo’s is almost 13 hours longer. Second, every city sits a few minutes above 12 hours at both equinoxes. That is not rounding, and it gets its own section below.
North of about 66.6 degrees, the Arctic Circle, the Sun stays up for at least one full day around the June solstice and stays down around the December one. Reykjavik is just south of that line, so in June its sun sets a few minutes after midnight and rises again before 3:00 a.m. The far north has its own article on midnight sun and polar night.
How fast days grow and shrink
Day length does not change at a steady rate. It changes fastest around the equinoxes and slowest around the solstices, because that is how the Sun’s declination moves: it races across the equator at about 0.4 degrees a day in March and September, then slows, stops and turns around in June and December.
| City | Around March 20 | Early August | Around June 21 |
|---|---|---|---|
| Singapore | +4 seconds | -4 seconds | under 1 second |
| Cairo | +1.8 min | -1.4 min | about 1 second |
| Paris | +3.6 min | -2.9 min | about 3 seconds |
| Oslo | +5.5 min | -4.9 min | about 7 seconds |
| Reykjavik | +6.5 min | -6.6 min | about 16 seconds |
This is why the weeks around the solstices feel static and the weeks around the equinoxes feel like the light is draining away. Between August 3 and September 3, Paris goes from 15 hours to about 13 hours 19 minutes of daylight, and Oslo from about 16 hours 39 minutes to just under 14 hours.
Sunrise and sunset do not move by equal amounts each day, either. Around the December solstice the earliest sunset comes a week or two before the shortest day and the latest sunrise a week or two after it, an effect of Earth’s elliptical orbit and its tilt that we explain in why the earliest sunset comes before the solstice. The same shift explains why the Sun is rarely highest at exactly 12:00; see solar noon.
What sunrise officially means
Sunrise is the moment the upper edge of the Sun’s disk appears on the horizon, not the moment the center does. That is the definition the U.S. Naval Observatory uses, and most almanacs and weather apps follow it. It assumes a level horizon at sea level and average atmospheric conditions.
Two corrections go into it. The Sun’s disk has an average apparent radius of about 16 arcminutes, so the top edge clears the horizon before the center does. The atmosphere also bends sunlight near the horizon by about 34 arcminutes on average, which lifts the image of the Sun into view while it is still geometrically below the horizon. Added together, sunrise and sunset are calculated for the moment the Sun’s center is 50 arcminutes below a flat horizon.
Those 50 arcminutes are worth a few minutes of daylight at each end of the day (about 5 in Paris at the equinox), more at high latitudes, where the Sun meets the horizon at a shallow angle. Real refraction varies with the weather, and mountains or buildings on your horizon delay the sunrise you actually see. Published times are a standard, not a promise for your window. The light before sunrise and after sunset follows separate definitions, covered in civil, nautical and astronomical twilight.
Equinox: not exactly 12 hours
The equinox is the moment the Sun crosses the equator, and its name means “equal night.” Geometrically, the Sun’s center is above the horizon for close to 12 hours that day everywhere. But sunrise is counted from the top edge, and refraction lifts the Sun early in the morning and keeps it visible late in the evening, so the day as published is longer than 12 hours: about 12 hours 7 minutes at the equator and Cairo, 12 hours 10 minutes in Paris, 12 hours 15 minutes in Reykjavik.
The day when daylight and darkness really are closest to equal is called the equilux. It falls a few days before the March equinox and a few days after the September one, and the date depends on latitude. In Paris, day length passes 12 hours between March 17 and 18, and drops back under 12 hours between September 25 and 26. Near the equator there is no equilux at all, since the day never gets as short as 12 hours.
Daylight on our city pages
Every city page on this site has a sunrise and sunset section that calculates the numbers above for that city’s coordinates. Open the current time in Paris as an example and scroll past the clock-change table:
- Today: sunrise, sunset, day length and solar noon for the current date.
- Daylight through the year: the four rows of the table above (both equinoxes and both solstices) in local clock time.
- The earliest sunrise and latest sunset of the year, with their dates. They rarely fall on the solstice itself.
- Clock time and sun time: how far the city’s clock runs ahead of or behind the Sun, and when solar noon falls.
Times on those pages include daylight saving time, so sunrise and sunset jump by an hour on the days the clocks change even though the daylight itself changes by a minute or two. For anything you plan around the light, like a hike that has to finish before sunset, check the date in question rather than today. The date calculator tells you how many days remain until a given date, and a countdown to the next solstice or equinox shows how long the days will keep shrinking.
For the shortest day of the year itself, see the winter solstice guide. To see how much light your own city is losing this week, open its city page and compare today’s day length with the September equinox row.
Frequently asked questions
Why do days get shorter after June 21?
After the June solstice the Northern Hemisphere starts tilting away from the Sun, so the Sun’s path across the sky gets lower and shorter each day. The loss is slow at first and speeds up toward the September equinox.
How much daylight do we lose each day?
It depends on latitude and date. In early August, Paris and London lose about 3 minutes a day and Oslo about 5; near the solstices the change drops to seconds.
Are day and night equal on the equinox?
Not quite. Because sunrise is measured from the top edge of the Sun and the atmosphere bends its light, the equinox day is several minutes longer than 12 hours at most latitudes.
Why does the sun set at different times in places on the same longitude?
Latitude changes the length of the Sun’s arc above the horizon. On the same June evening, a city farther north sees a later sunset and an earlier sunrise than one farther south.
Every date, offset and calculation on this page was checked against the sources below.