Equinox (from the Latin, meaning 'equal night') is an astronomical notion referring to the moment when the sun crosses the equator. After that moment during the autumnal equinox (falling either on 22 or 23 September), the sun sheds more light on the Southern Hemisphere; after the vernal equinox (which occurs on 20 or 21 March), the sun sheds more light on the Northern Hemisphere.
We have been led to believe that on those two days of the year, every point on earth receives exactly 12 hours of daylight, and night is exactly 12 hours long.
This is not so. At our latitude, this actually happens a few days after the autumnal equinox and a few days before the vernal equinox. Looking at Warsaw, for example, the day on which we get nearest to a 12/12 split is today, the 25th of September, when the sun rose this morning at 06:27 and will set at 18:26. On Sunday, the day of the autumnal equinox, there was still 11 minutes more day than night. We have the same situation in spring; equilux occurs three days before the vernal equinox (sunrise at quarter to six am, sunset quarter to six pm). On the day of the vernal equinox, there's already 11 minutes more day than night.
So on the scale of a year, we have 27 weeks with more day than night, and 25 weeks with less day than night. Which is quite a good deal given that in theory it should be exactly half and half. A reminder that in the cosmic scheme of things, Light triumphs over Darkness.
Below: the evening before Equilux, between Chynów and Węszelówka.
Below: awaiting the last sunset to be separated by less than 12 hours from the next sunrise until 18 March 2025.
Out of interest: in Macapá, Brazil, a town which straddles the equator, the year's longest day is 12 hours, 7 minutes and 28 seconds (on 21 June); on the year's shortest day it is but 12 hours, 7 minutes and 21 seconds (on 21 December). Meanwhile, in Longyearbyen on the island of Svalbard, the town nearest the North Pole, the longest day lasts five months and six days – from sunrise on the morning of 19 April until the sun finally sets on the evening of 25 September. And the sun never rises above the horizon here between 26 October and 15 February. These disparities occur because the Earth is tilted at 23 degrees to the sun; the North Pole is closest to the sun on 22 June, the South Pole on 21 December, and on 20 March and 22 September, the earth faces the sun side-on.
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