The Vernal Equinox Isn't What You Think It is

Tomorrow is the vernal equinox! 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 Okay 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.


Andrew Liptak is the former Weekend editor of io9/Gizmodo. He is the co-editor of War Stories: New Military Science Fiction and hails from Vermont.


A Pimp Named DaveR

You can’t be perpendicular to a sphere.*

The equinox is when the equator is parallel to the Earth’s orbital plane. (Or, if you prefer, when its rotational axis is perpendicular to its orbital plane.)

*Well, you can — but you’re actually perpendicular to a plane that intersects the sphere.