The autumn solstice arrives Tuesday at 8:05 p.m. Eastern time, marking the seasonal turn for the Northern Hemisphere. At that moment, the Southern Hemisphere moves into spring, while the sun sits directly overhead at the equator at noon.
Day and night are almost the same length, which is why the word equinox comes from two Latin words meaning equal and night. The balance is close, not perfect: depending on where you are on Earth, one side of the day can run a few extra minutes longer.
Earth and the equator
During an equinox, Earth’s tilt is neither toward the sun nor away from it. That is the difference from the solstices, when Earth is tipped most extremely toward or away from the sun. The result is also easy to spot: the sun rises almost exactly due east and sets almost exactly due west.
Equinoxes are the only times when both the north and south poles are lit by sunshine at the same time. For readers watching the calendar, the autumnal equinox can land between Sept. 21 and 24, and this year it falls at 8:05 p.m. Eastern time Tuesday.
Summer solstice and winter solstice
The solstices frame the other extreme of the year. The summer solstice in the Northern Hemisphere falls between June 20 and 22 and brings the longest day and shortest night. The winter solstice falls between Dec. 20 and 23 and brings the shortest day and longest night.
That contrast is why astronomical seasons follow the sky rather than a clock or a weather report. Meteorological seasons start on fixed dates instead — March 1, June 1, Sept. 1 and Dec. 1 — but the autumnal equinox marks the astronomical start of fall in the Northern Hemisphere.
People in the Northern Hemisphere
People in the Northern Hemisphere get the season change first on Tuesday, and the shift is nearly simultaneous across the globe because the exact time is the moment the sun is directly overhead at the equator. Around that instant, day and night seem close to even, yet location still nudges the count by a few minutes.
The next seasonal turn will follow the same pattern, with the date moving within the usual late-September range. That changing window is the part readers can watch: the sky keeps the rule, even when the calendar date slides a little year to year.
