The Equinox Is a Moment, Not a Day

He breaks down what the equinox actually is: not a day, but a fleeting instant. Most people think of March 22nd as the equinox, but technically it's the precise moment when Earth's zero longitude line crosses the local meridian. That moment can be measured down to a second, a hundredth of a second, even a millionth of a second, because the planet never stops rotating. The equinox is the hypothetical point that divides the cycle exactly in half: 43,200 seconds of daylight, 43,200 seconds of darkness. It's a geometric reality, not just a calendar date. Understanding this precision helps clarify how ancient cultures tracked celestial mechanics with such accuracy.