Autumnal Equinox Hits 23 Sept — But Day and Night Aren't Equal — SkimNews
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- The autumnal equinox falls at 01.05 BST on 23 September, marking the astronomical start of autumn in the northern hemisphere and spring in the southern hemisphere.
- The equinox is defined as the moment the sun crosses the celestial equator — Earth's equator projected into the sky — shifting its apparent position from north to south.
- Day and night are not precisely equal at the equinox despite the Latin meaning "equal night": the sun's disc and atmospheric refraction make measured daytime several minutes longer than 12 hours.
- The UK equilux — the date day and night come closest to being equal — falls around 25 September, a couple of days after the equinox itself.
Why it matters: For skywatchers and calendar-dependent industries, the 23 September equinox is the fixed astronomical marker, but the source underscores that equal-daylight doesn't arrive until around 25 September in the UK — a nuance the word "equinox" literally contradicts.
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