Weather 101: What causes the seasons?

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You don’t need a calendar, you can tell based on the temperatures and the feel in the air. Fall is here. But what causes the change in the seasons? The earth is tilted at 23.5 degrees, allowing for parts of the planet to receive different amounts of daylight depending on the time of year.

Meteorologist Brandon Weathers explains. There are two points of the year where we have the center of the sun directly over the equator. When this happens, we get roughly 12 hours of daylight from pole to pole.

Then there are our solstices. The summer solstice is when we have the center of the sun directly over the Tropic of Cancer. This gives us the longest day of the year here in the Northern Hemisphere.

The Arctic Circle gets about 24 hours of daylight, and the equator still receives roughly 12 hours. At our latitude in the Northland, our longest day is around 16 hours.

Now we flip to the other side, that is the winter solstice. It’s our shortest day of the year because we have the center of the sun directly over the Tropic of Capricorn. That’s when we have roughly 8 and a half hours of daylight in the Northland.

The autumnal equinox is at 2:20 pm on September 22nd this year. Both the time and the day fluctuate based on the exact time the center of the sun is over the equator.

The Latin root of "equinox" translates to "equal nights." This is the astronomical first official day of fall. For meteorology, we do it just a little bit differently. We break up the seasons based on the months.

We have the three coldest months of the year as winter; December, January, and February. The next three months mark spring; March, April, and May. Summer is the three warmest months of the year, so that’s June, July, and August. Fall includes September, October, and November.

So, meteorologically, the first official day of fall is September 1st. The last official day is November 30th.