Today is the autumn equinox, the date in astronomy that marks the start of autumn. Day and night will be roughly equal in length, and the nights across the northern hemisphere will be longer than daytimes outside of the polar regions until the winter solstice, the shortest day of the year, on December 22 this year.

In meteorology, though, autumn begins on September 1 and ends on November 30, because the seasons of the year are split into three-month segments to make it easier for comparing seasonal and monthly figures.

The hours of day and night at the equinox are not exactly equal because there is extra daylight, ranging from a few minutes at the equator to more than 20 minutes nearer the poles.

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