Video: Yesterday was the vernal equinox, or the autumnal equinox for those of us in the southern hemisphere. You might think that it's simply the mid-point between each solstice, but that's not exactly correct. Joe Hanson, host of It's OK to be Smart, explains.
The equinoxes aren't in the middle of the solstices, and it doesn't mean that day and night are exactly equal. It's the point in the year when the Earth's equator is perpendicular to the sun. There is a point when day and night are equal: that's the Equilux, which happens a couple of days before each Equinox.
Why is this? The Earth's atmosphere helps reflect sunlight, and the sun is a large disk: not a point, so when it's rising, the point at which it's perfectly perpendicular isn't right at sunrise.