Would you like to feel joy? Let me recommend watching at least a little of this Friday's lunar eclipse. We all know how astronomy can make us suffer at times. That might mean cold or hot weather, mosquitos, high winds, battles with clouds or trooping out in the middle of the night
For much of North America the eclipse takes place after midnight. And given that we're well into November the temperature will likely be below freezing. So yes, there might be some suffering involved. But I'm here to tell you that despite the inconvenient hour your time will be well spent. Even if you just poke your head out for a few minutes.
A lunar eclipse only occurs at full moon, when the moon lines up directly behind the Earth and passes through its shadow. Here on the ground, you can watch the planet's shadow rise along the eastern horizon at sundown any clear evening. It looks like a purplish-gray band and reaches halfway around the sky. The shadow has two parts — an inner, dark umbra, where the globe of the Earth completely blocks the sun, and an outer penumbra. In the outer shadow, the Earth only partially covers the sun, so some sunlight leaks into and dilutes the shadow.
We barely notice the moon passing through the penumbra until it gets quite close to the umbra. About 20 minutes beforehand, the encroaching edge appears oddly blunted and dusky gray. But the moment the moon treads into the umbra, the eclipse is obvious, as the inner, inky shadow "bites" darkly into the moon's edge.
Both shadows stretch far into space behind the Earth. The penumbra expands with distance while the umbra narrows like a wind sock. At the moon's average distance of 239,000 miles (384,600 km), the umbra is just 1.3° across or 2.6x the apparent size of the full moon. If the moon orbited in exactly the same plane as the Earth, all three bodies would precisely line up in a row at full moon, and we'd see a total eclipse every month.
But this isn't what happens. Why? The moon's orbit is tilted 5.1° with respect to the Earth's orbit. As it circles the planet, it typically passes above or below the shadow, and we see a big, bright, uneclipsed moon instead. Now that you know how narrow the umbra is at the moon's distance it's easy to see why the moon often misses its target. An eclipse, especially a total one, is like hitting the bulls-eye.
We usually get two lunar eclipses a year, though in some years it's three or none. This number includes purely penumbral eclipses where the moon passes through the outer shadow only, completely missing the umbra. Friday morning's eclipse will be much better but still not total. At 3:03 a.m. CST, 97 percent of the moon will huddle within the Earth's inner shadow. Only its bottom edge will poke into the penumbra.
The good stuff
Since it's a near-total eclipse, we'll get to see all the good stuff. That includes watching the moon turn that signature orange-red color as it dips deeper and deeper into the shadow core. This should become obvious when the umbra covers about a third of the moon. The sky will also transition from harsh moonlight and deep shadows to true darkness. Shadows cast by the moon will vanish around mid-eclipse, and all the stars will return as if the moon had departed the sky.
The striking eclipse colors come from sunlight that "leaks" around the edge of the Earth, refracted by the atmosphere. Since sunlight skirts the edge of the planet, the violets, blues and greens in the light are scattered away just as they are at sunrise and sunset, when the sun hovers near the horizon. Only the "longer" wavelength hues of yellow, orange and red pass. The air bends and sends these colors into the umbra to paint the moon. Miraculous.
From first to last penumbral contact, the eclipse will last more than six hours! I can't imagine anyone investing that much time in a lunar eclipse. I plan to start watching around 1 a.m. about 20 minutes before the partial eclipse begins at 1:18 a.m. CST, so I can spot the grayish penumbral shadow along the moon's upper left edge. I'll stay past mid-eclipse for sure and maybe watch until the partial eclipse wraps up at 4:47 a.m. for a total of about 3 1/2 hours.
You can chose your own time slot. But if you want just the cream, plan on being out between 2:45-3:15 a.m. CST (3:45-4:15 a.m. Eastern; 1:45-2:15 a.m. Mountain; 12:45-1:15 Pacific and 11:45 p.m.-12:15 a.m. Alaska Standard Time) During that half-hour, the moon will slide into mid-eclipse (when it's darkest) and then slowly begin to exit, the same way you'll get out of bed and then return to it. From most U.S. and Canadian locations the moon will stand high in south-southwestern sky at this time.
Some sisterly help
By dint of good luck, the eclipsed moon will appear just 6.5° below the bright, beautiful and familiar Pleiades star cluster, also called the Seven Sisters. What a gorgeous pairing! If you have good mobile phone or a DSLR / mirrorless camera, place it on a tripod and make a pretty scene with the duo aglow over a local landscape. I've included an exposure table based on using ISO 800, a good, all-around speed for capturing every aspect of a lunar eclipse.
Bring binoculars! With them you'll see stars right up near the moon's edge, something otherwise impossible during a typical full moon. The sight makes our satellite appear as if it's floating in three dimensions. Binoculars will also reveal more subtle color hues on the lunar disk. If you have a telescope, you can watch the Earth's umbra "eclipse" prominent craters as the moon plows eastward at 2,300 miles and hour (3,700 km/hour).
What if clouds pounce?
You can check the weather in advance, and if clouds threaten, attempt to escape to a clear location by car. The Weather Network offers a handy, interactive cloud viewer or you can check the U.S. 7-Day Cloud Cover Forecast. If bad weather means your stuck at home, Gianluca Masi will live stream the eclipse on his Virtual Telescope site on Nov. 19 starting at 1 a.m. CST (7:00 Greenwich Time).
To track current clouds I like the GOES-East satellite imagery, which provides excellent coverage of the eastern two-thirds of the U.S., southern Canada, and Central America. There's also a GOES-West version. At night, the map will appear black unless you click on the Choose bar and select Channel 7. This provides an infrared view that lets you see clouds in total darkness.
Let's all hope for good weather. And if we lose this one to clouds, no worries. There will be two TOTAL lunar eclipses next year in May and November.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.