On the night of November 18th/19th (Thursday night and Friday morning), folks with clear skies across America will be treated to a near-total lunar eclipse. The eclipse begins officially just after 11 p.m. Mountain Time on the 18th when the Moon first begins to move into the Earth’s shadow, and slowly darkens as it receive progressively less and less sunlight. Things won’t get visually interesting, however, until around 12:20 a.m., when the first portion of the lunar face enters the umbral shadow where all direct illumination is obscured by Earth. The Moon’s surface remains feebly lit only because of all of the sunrises and sunsets happening around the globe at that moment: the red rays that survive passage through our atmosphere are refracted or bent slightly to strike and illuminate the lunar surface.
Total lunar eclipses occur, on average, about once every 27 full moons for any given observer; they actually happen twice that often, but half the time we’re on the wrong side of the Earth to observe them. And although the upcoming eclipse will not quite be total, it will be nearly so: At 2:03 a.m. Mountain Time, all except 2.6% of the lunar face will be completely immersed in the Earth’s shadow. That small sliver remaining in sunlight will have dimmed a hundred-fold or more from its appearance a mere three hours earlier.
Because total shadow coverage won’t happen, the eclipse will be relatively bright: the lunar surface will likely appear coppery in color, rather than the dim ashen gray or ghoulish red which is so often touted in the popularized “blood moon” moniker regarding these events. Quite honestly, for me at least, that’s a pretty good thing. It’s actually somewhat boring to watch a deep dark central lunar eclipse unfold, where the Moon dims some 20,000-30,000 times from its former luminosity, and can barely be picked out of the sky as a dark round disk. I much prefer the view of the eclipsed moon just as it approaches or enters totality, where there are distinctly different variations of ruddy shades spanning the disk, and craters and maria are still bright enough to be seen; it’s much more colorful, while still allowing you to see adjacent background stars that were formerly obscured by the glare of the brilliant full moon.
And that’s where this particular eclipse should appear even more pleasing, because it will occur between two of our most distinct and recognizable star clusters: the Pleiades and the Hyades in the constellation of Taurus the Bull (see https://lyonsrecorder.org/2021/01/28/two-clusters-age-of-a-star/ ). Given clear skies, this may be the most “stellar” lunar eclipse photo-op you’ll ever experience!
One final observation about that sliver of sunlight that will remain on the southernmost limb of the Moon: it will fall directly on the crater Cabeus in the Lunar Highlands. We’ll not be able to make out the crater itself, even with a telescope, since we’ll view it obliquely and only see its illuminated rim from the side. But that’s what makes the crater so interesting, since its interior is forever shielded from sunlight by its rim.
Cabeus got the world’s attention in 2009 when controllers of the spacecraft LCROSS (Lunar Crater Observation and Sensing Satellite) intentionally smashed its upper stage Centaur rocket into the crater floor at over 5,000 mph, and then searched the resultant plume for water that had been trapped there as permafrost … before it, too, slammed into the crater four minutes later. Future human colonies are likely to be constructed here, perhaps the only place on the Moon where water could potentially be mined from the lunar depths instead of being imported from Earth.