Last night, at precisely 11:48 am, a very special thing happened: the Sun crossed Earth’s equator. This is what it looks like, courtesy of Astronomy Picture of the Day:
Now that explanation might not make a whole lot of sense. To understand it, you need to know a few things. Or be reminded of them.
First of all, recall that Earth spins. It spins about an imaginary pole (well, two of them if you include the north and south poles), the official term for which is axis. When that axis is directly up an down (vertical) with respect to our orbit around the Sun, the the Sun shines down directly on the equator.
(Here’s an animation that illustrates what we’re talking about here.)
And that’s what happened last night. The vernal equinox. Equal nights.
The upshot of all this is that spring has sprung. From here on in, the days become longer and the nights shorter. In 91 days we’ll have the longest day (and shortest night) and the days will begin to get shorter again.
Happy spring!
Additional Resources
An explanation of Earth’s Rotation (Wikipedia).
Motion of the Earth (from the Office of Naval Research).
