view of Earth from the moonAn exotic and beautiful new word is reason enough to write about. Equilux. It’s the day of the year when light and dark are equal (not Equinox). I felt like celebrating Equinox and looked it up – only to be astounded at how much I’d forgotten or never known.

The celestial mechanics literally disoriented me in time and space: the constant 23-degree tilt of the Earth toward Polaris modulates our day-night experience as we whirl around the Sun every year. We always have the same attitude, so to speak, but on one side of the orbit around our home star, our tilt means the north is leaning away from the Sun, and on the other side of the orbit, the same tilt means the north is leaning toward the Sun – which makes our seasons a function of where we are along our annual orbit, not unilaterally changing our tilt to the north or south. I enjoyed getting unsettled by the relativity of it all (the same attitude having opposite effects in opposite environments). Maybe most educated grownups already internalized all this, but I’d never fully focused on it before.

Equinox, at 7:21 a.m. MST on Thursday, September 22, 2016, is the moment, halfway between solstice extremes, when Earth’s ecliptic – the plane fanning out from the equator – is perfectly aligned with the center of the Sun, not tilted toward or away. This alignment, this central energetic attunement, was thrilling to me. (Illustrations are at timeanddate.)

Still, there’s something mystical about a perfect balance of light and dark, which turns out to be Equilux – equal light. The timing of it varies with a location’s latitude, influenced by sunlight’s bending through our atmosphere (which lengthens the days). I’m writing this near the 35th parallel, where the chart says Equilux will happen on September 26 – although another source says we’ll have a perfect 12-hour day on September 25. It’s easy to see how European cultures, on roughly the same parallel, blended the phenomena into a single idea. Near the Equator, Equilux is October 17. I’m still fascinated with how differently we can all experience something so literally central to our lives, so overwhelming, in such different ways, depending on our literal point of view.

The sky dance of Earth and Sun got a little more intricate and relativistic for me, and it seems like a fun fact to share. So best wishes for a blessed Equinox and mystical Equilux, wherever you are, whenever it happens.

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PS: If you enjoy spatial disorientation, you might have a good time with “Approaching Solstice” – which not only gives our spinning speeds, but links to a map that explains why the Northern Hemisphere is not necessarily on top.