Daylight does not drain away at a steady rate. It falls in a curve, and in early September you are standing in the steepest part of it.
Here is the shape of it. The earth's axis is tilted a little over 23 degrees, and that tilt points the same direction all year, like a spinning top holding its lean as it wanders across a table. In June, our part of the globe leaned towards the sun and the night nearly vanished — the same tilt behind why summer nights stay light. The planet has since moved on around its orbit, and we lean towards the light a little less each day.
That much is the standard explanation. It hides something.
Think of the year as a sledding hill rather than an even slope: a flat top, a steep middle, a long run-out. Midsummer is the flat top. In late June the day was getting only about one minute shorter every twenty-four hours - too little for anyone to notice. Now you are on the steep section, and in southern Norway the day is shrinking by roughly five minutes every single day. Five times faster than in June.
That is why autumn feels like it arrived overnight. It very nearly did. And the hill gets steeper still before it levels out: the fastest point of the whole year lands around the autumn equinox, close to 23 September.
Why this matters for children
It hands a child one of the most useful tools in all of science: the difference between how much of something there is and how fast it is changing.
A child can already tell you it gets darker in autumn. That is an observation. Noticing that the dark is arriving faster now than it was in July is something else entirely - that is measuring a rate, not a state. The same habit of mind sits underneath growth charts, epidemics and climate science. The thinking behind turning everyday moments into science is gathered in What is STEAM learning?.
Try it at home: measure the hill yourself
You need a sheet of paper, a pencil, and ten seconds a day.
Write down today's sunset time with the date in front of it. Do the same tomorrow, and the day after. After three days, work out how many minutes earlier the sun set than on day one, and divide by three. That number is yours - your own measurement of the slope.
Keep going for two weeks and let your child draw the times as a staircase down the page. Are the steps the same size, or are they growing?
Watch what happens around day five, when the number stops being a grown-up's task and becomes the child's own.
What happens if you keep measuring all the way to Christmas?
Every child is made of good atoms. At Good Atoms we help them discover it, one evening at a time.
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