Happy Equilux!
Though equinox means "equal night" in Latin, the day when the Sun spends nearly equal time above and below the horizon, or equilux, happens days before the equinox and that day varies by location
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The Vernal Equinox arrives on Sunday March 20, 2022 at exactly 11:33 am EDT. This is an instant in time which occurs world wide when the Sun is directly over the equator.
On this day, the terminator or the line separating day from night runs vertically from north pole to south pole. This animation of the terminator moving during the day of a recent equinox shows that line very clearly.
Equinox is Latin for "equal night", but that doesn't also mean "equal day".
That day is the equilux, Latin for "equal light", or when as close to exactly 12 hours of daylight as possible, happens a few days before the March equinox and a few days after the September equinox because:
The Sun is not a point in the sky, it's a disk The scientific definition for the time of sunrise, as defined by the United States Naval Observatory, is when the top edge of the Sun is first visible (at sea level). Similarly, the definition of sunset is when the top edge drops below the horizon. With the Sun's disk measuring about 1/2º wide, provides 2-3 minutes more sunlight each day, shifting the date of equilux
The atmosphere refracts or bends sunlight, making the Sun appear on the horizon while it is still physically below the horizon.
The equilux is today, March 16 for the Carolinas and most of the United States south of a line stretching from southern Virginia to the San Francisco bay area. Here in Raleigh The difference between sunrise and sunset was 11 hours 59 minutes and 6 seconds and The days continue to get a little longer, by 2 minutes and 16 seconds each day.
For northern states it is tomorrow, March 17 and for southern Florida and Texas it was yesterday March 15.
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