Why the days are getting shorter so fast right now, up to 4 minutes a day
By Sam Arkwell · published September 9, 2026
Everyone says it in the office corridors this time of year: “is it just me, or is it getting dark all of a sudden?” An astronomer’s answer: it is not just you, and “all of a sudden” is measurably correct. These are the weeks when the northern hemisphere loses daylight faster than at any other time of the year, up to 4 minutes per day depending on where you live. Here are the exact numbers, the elegant geometry behind them, and the calendar of what comes next.
The fastest slide of the year, in numbers
Let’s put figures on the feeling. Around this September 9, a mid-northern city loses roughly 3 minutes of daylight every single day: about 2.5 minutes in Los Angeles, 3 in New York, closer to 4 in London, and more than 5 in Stockholm. Trivial per day, spectacular in accumulation: 20 to 28 minutes gone every week, and up to two hours across the month of September. If sunset seemed fine when school started and feels alarmingly early now, that is not memory playing tricks: the evening sun has retreated by a full quarter of an hour per week.
This is the annual record. No other stretch of the calendar moves this fast, and the phenomenon has an exact mirror in late March, when daylight returns at the same breakneck pace and everyone marvels that “the evenings are suddenly longer.” March and September are the two great daylight toboggans of the year, one up, one down.
Latitude sets the steepness. Near the equator, day length barely changes all year, Miami is losing under two minutes a day; the further north you live, the harder September pulls, which is why Scandinavians feel autumn arrive like a curtain drop. Your slide is, quite literally, a function of your address.
The wave: why everything peaks at the equinox
The explanation fits in one image. Chart day length across the year and you get a smooth wave: crest at the June solstice, trough at the December one, crossing the twelve-hour midline at both equinoxes. And a wave has a property every surfer knows: it is flat at its peaks and steepest in the middle. At the solstices, day length stalls, the word itself means “sun standing still”, and late June loses mere seconds per day. At the equinoxes, we ride the steepest section: the daily change hits its maximum.
That is exactly where we are: two weeks from the September 23 equinox, when the Sun crosses the equator and day and night briefly equalize at twelve hours everywhere on Earth. The slope is already near maximal and stays there into early October, then relaxes month after month: November shrinks noticeably slower, late December barely at all, until the full stop of the December 21 solstice, the year’s shortest day. From there, the whole ride reverses, minute for minute.
One more date will hit your evenings harder than any astronomy: the clock change. Europe falls back on October 25 and most of the US on November 1, shoving sunset an hour earlier overnight. Nature nibbles 3 minutes a day; the law swallows an hour before breakfast. The famously “sudden” dark evenings of late autumn are mostly a legal artifact stacked on an astronomical slide.
Riding the slide: three seasonal habits
The toboggan is not just trivia: your body clock runs on light, and every autumn chronobiologists log the season’s toll of drifting bedtimes and dipping moods as the mornings dim. Three habits smooth the ride.
Bank morning light first, it has become the scarce resource: fifteen minutes outdoors before noon anchors the internal clock better than any coffee, and September still has plenty to give. Shift outdoor plans earlier as the weeks pass: the evening run that fit comfortably before dinner in August will be a headlamp affair by October, and lunchtime is the new golden hour. Keep a steady sleep schedule finally, the universal shock absorber: a regular bedtime and a reliable alarm help the clock digest the slide instead of chasing it.
And keep the astronomer’s consolation in mind: this is a round trip with a guarantee. Every minute leaving now is already booked for return next spring, on schedule, and the rebound starts December 21 to the second. The sky is the one institution that always pays you back in full, exact time included.
Your questions
How much daylight are we losing per day in September?
This is the fastest stretch of the year: around 2.5 to 4 minutes of daylight lost per day depending on latitude (about 2.5 in Los Angeles, 3 in New York, 4 in London), which adds up to 20 to 28 minutes a week. No other month shrinks the evenings this quickly, and the sensation that night suddenly falls earlier is astronomically accurate.
Why is daylight loss fastest around the equinox?
Day length follows a smooth wave through the year: nearly flat at the solstices (days barely change in June and December) and steepest halfway between, at the March and September equinoxes. Around September 23 we slide down the steepest part of the wave, so each day loses the maximum possible amount.
When do the days stop getting shorter?
At the winter solstice, around December 21, the shortest day of the year. The pace of loss, maximal now, eases month by month: November already shrinks more slowly and late December barely changes at all before the trend reverses. Clock changes add their own jolt: Europe falls back on October 25, most of the US on November 1, pushing sunset an hour earlier overnight.
Is the effect the same everywhere?
No, it grows with latitude. Near the equator day length hardly varies all year; Miami loses under 2 minutes a day right now, London about 4, and Stockholm more than 5. The further from the equator you live, the steeper your September slide, and the bigger your December-to-June swing.