Guide

Happening unseenSky

How fast the days get shorter in fall

September to November

Daylight is shrinking by one to three minutes every day, about 20 minutes a week at the quickest stretch. The loss is biggest in the weeks around the fall equinox and fades to almost nothing near the winter solstice.

Why this time of year

Between the fall equinox and the winter solstice every day is shorter than the one before, and for several weeks after the equinox the loss runs close to 20 minutes a week.

How to notice it

  1. Look up today's sunset and sunrise in a weather app or sun table and write down the day length: sunset minus sunrise.
  2. Do it again in exactly one week and subtract. In this season the difference is usually about 11 to 21 minutes, largest in late September and early October.
  3. Compare the two weeks by day length, not by the clock: when clocks fall back an hour in early November, sunset jumps an hour earlier on the clock, but the day itself only lost its usual few minutes.
  4. Come back near the winter solstice and repeat: the weekly loss will have shrunk to a few minutes or less.

Try this with kids: Can you catch the day getting shorter? Write down how long the sun is up today, then check again next week. How many minutes did we lose?

Word to know: “Equinox” means the two days a year when day and night are nearly equal; solstice means the day with the most extreme (shortest or longest) daylight.

Sources

  • aa.usno.navy.milUSNO API at 42.36N 71.06W, standard time. Day length (set minus rise) from this and same-endpoint queries for other dates: Aug 1 14:27; Aug 15 13:53; Sep 22 12:09; Sep 29 11:50; Oct 6 11:30; Oct 13 11:10; Nov 1 10:19; Nov 15 9:47; Dec 1 9:19; Dec 15 9:06; Dec 21 9:05. Weekly losses about 19-20 min Sep 22 - Oct 13; about 2.7/day Oct 13 - Nov 1; about 2.3/day Nov 1-15; about 1.75/day Nov 15 - Dec 1; about 0.9/day Dec 1-15.
  • aa.usno.navy.milUSNO: 2026 September equinox Sep 22, December solstice Dec 21.
  • wxguys.ssec.wisc.eduUW-Madison SSEC Weather Guys: day length changes fastest at the equinoxes and essentially not at all day to day at the solstices.
  • nist.govNIST: daylight saving time ends on the first Sunday in November (November 1 at 2 a.m. in 2026), when clocks fall back one hour; supports the clock-change caveat in step 3.

Checked against these sources on October 6, 2026.

In the guide for September, October, November

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