Weather IQ: Do We Actually Have Equal Day and Night on the Equinox?
Atmospheric refraction and the sun’s disk add several minutes of daylight, so the equilux usually falls days after the equinox, astronomers said.
- On Sept 23, 2026, the Northern Hemisphere experiences the autumn equinox. Contrary to popular belief, daylight actually exceeds nighttime, lasting longer than 12 hours.
- Because the sun appears as a disk rather than a point, sunrise and sunset are defined by its edges touching the horizon. This geometry adds several minutes of daylight to the day.
- Earth's atmosphere acts like a lens, refracting sunlight to uplift the sun about 0.5 degrees. This effect advances sunrise and delays sunset, contributing nearly another six minutes of daylight at mid-temperate latitudes.
- Defining the day when daylight and night are truly equal, the "equilux" occurs a few days after the autumn equinox. This date varies by latitude.
- In Maine, the equilux occurs on Friday, Sept 25, 2026, several days after the equinox. These localized dates show the transition to longer nights happens gradually across regions.
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Are day and night equal on the equinox? Not exactly
Are day and night equal at an equinox? No. Earth's atmosphere and our sun team up to give us more day than night during an equinox. The post Are day and night equal on the equinox? Not exactly first appeared on EarthSky.
Scientists have explained why the day of the autumn equinox isn't equal to the night.
The equinox takes place on September 23, 2026, marking the official beginning of the astronomical autumn. On this day, the sun crosses the celestial equator, which makes day and night almost equal as a duration, but not perfectly equal as has been thought so far. Millions of people associate the autumn equinox with the perfect moment in which the duration of the day becomes equal to that of the night. The term comes from Latin, where "aequus is …
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