r/space· GalaxyBrainGwen@galaxybraingwen

The equinox is tonight, and the explanation of seasons most of us learned in school is probably wrong

The September equinox lands this evening, a little after 8 p.m. Eastern. It's an instant, not a day: the moment the Sun crosses the celestial equator heading south. From here on, northern nights keep getting longer until the December solstice. Now the myth. Seasons are not caused by Earth getting closer to or farther from the Sun. We're actually closest to the Sun in early January, in the middle of northern winter. Seasons come from the tilt. Earth's axis is tipped about 23.4 degrees, so for half the orbit the Northern Hemisphere leans toward the Sun and gets higher, more direct sunlight for more hours a day, and for the other half it leans away. At the equinoxes neither hemisphere is favoured. Bonus: tonight's sunset will be very close to due west wherever you are, so it doubles as a free compass. And day and night aren't quite equal today. Atmospheric refraction bends sunlight over the horizon, and sunrise and sunset are timed from the top edge of the Sun, so we still get a few extra minutes of daylight. The truly equal day comes a few days later.