Lunar | Solar

The Full Beaver Micro Moon occurs at 01:05 PST on November 19th, but at that moment it’s obscured by the Earth’s shadow. This lunar eclipse is notable due to its extended duration. The event begins as the Moon passes into the penumbra, Earth’s wider shadow, at about 22:02 on the 18th. Then, at 23:18, it moves into the umbra, the conical shadow, the point of which produces total eclipses. (This however is a deep partial eclipse.) The Moon exits the umbra at 02:47, and the penumbra at 04:03. That’s some three-and-a-half hours beneath the small shadow, and six hours in all! Much longer than usual.

It happens this way because the lunar orbit is slightly elliptical, and is approaching apogee on November 20th. This apogee is the Moon’s farthest excursion from the Earth (hence Micro), and because its farther afield, its orbital pace is slowed by Earth’s gravity. As such, it takes longer to move through the Earth’s shadow than, say, at near perigee where gravity is then accelerating the Moon.

This eclipse is nearly total as some 97% of the lunar disk is in shade, but even so, instead of being blotted out of the sky the Moon may take on a ruddy tint. This is because the sunlight passing through the Earth’s atmosphere is refracted & diffused providing faint illumination of the lunar surface. The bending and scattering of light leaves only dim lunar reflection of mostly longer wavelengths.

Several orbital cycles co-mingle to produce lunar phenomena, and one is known as a Draconic or nodal lunation. This cycle last about 27.21 days, which is shorter than the 29.53 days of the Synodic month— the lunation with which we are most familiar. New Moon to New Moon. When cycles coordinate, just so, syzygy occurs. That’s the horizontal / vertical alignment of the Sun, Earth, and Moon that results in eclipses. But it’s never just a single eclipse, it’s at least two. Lunar & solar. Each within about two weeks of each other. This happens when the New or Full Moon coincides with the Moon’s crossing of the ecliptic (the plane of the Earth’s path around the Sun).

You see, the Moon’s orbital path is tilted 5.14° to the ecliptic, and twice each month the two paths intersect. Each crossing is called a node, and there the Moon is at 0° ecliptic latitude. That is, on the same horizontal plane as the Earth and Sun (though not necessarily aligned longitudinally). As you know, a New Moon occurs when the Moon moves precisely in between the Sun and the Earth. And, a Full Moon occurs when the Moon makes its way to the far side of the Sun, Earth, Moon geometry. These are the longitudinal orientations. So, when these horizontal and vertical coordinates combine, say, for the Full Moon, the Earth gets in the way. Direct sunlight is blocked, and the effulgent lunar surface is cast into shade.

This is what’s going on right now. (As I’m writing this the Moon is just 1° below the ecliptic.) By 01:05 tomorrow morning the Moon reaches nearly 0° ecliptic latitude, and as its counter-clockwise orbit brings it into vertical alignment. Voila! An eclipse. Naturally, in two weeks, as the Moon is crossing the node 180° opposite this one, it eclipses the Sun. These coupled crossings are known as eclipse seasons, and are about half a year apart. This makes for generally four eclipses a year. Every so often there are more. Up to seven! (The last seven in 1982. The next in 2038.)

Those beavers, busy damming their rivers under November moonlight, might miss this celestial event. But you don’t have to. The evening’s streaming Zoom Yin yoga, a Full Moon class (usually quite Yang, and active), will be more of a New Moon class (fully Yin, and still), in accordance with this deep partial eclipse. Come joint in! Opening bell at 19:00 PST. Class lasts about an hour.