Friday evening, the Full Snow Moon will look a little weird when it rises in the eastern sky at sundown. That’s because for much of the U.S., the moon will already be in eclipse. Our favorite and only natural satellite slides through Earth’s outer shadow or penumbra that evening.
During a partial or total lunar eclipse, the full moon passes first through the Earth’s penumbra, before entering the dark, interior shadow or umbra. The penumbra is nowhere near as dark as the inner shadow because varying amounts of direct sunlight filter into it, diluting its duskiness. The penumbral shadow doesn’t take a “bite” out of the moon the way the umbra does but shades it instead. To your eye, the moon appears dimmer and blunted but not blackened.
The leading edge of the moon (east-facing of left side) first enters the penumbra on Friday at 4:34 p.m. Central time, an hour before sunset for the Midwest. Most of us won’t see the eclipse until moonrise nearly an hour later. By 5:30 p.m. local time, when the moon is staring at us from low in the eastern sky, you’ll detect the shadow as a subtle darkening of the left half of the lunar disk.
By 6:44 p.m., when the moon is deepest in the penumbra and closest to the umbra, the top half of the moon will appear noticeably darker than the bottom. As the moon rises ever higher in the sky, it moves through the outer shadow traveling at 2,290 mph, finally exiting the penumbra at 8:53 p.m.
From start to finish, the eclipse lasts more than 4 hours, but the best part is the hour and a half centered on maximum eclipse when the penumbral shading will be most obvious. That would be from 6-7:30 p.m. Central; 7-8:30 p.m. Eastern; 5-6:30 p.m. Mountain and around moonrise Pacific Time. If you can’t devote that amount of time, at least check out the scene between 6:30-7 p.m. Here are the particulars:
Eclipse begins: 4:34 p.m. CST (22:34 p.m. UT)
Maximum eclipse (moon deepest in shadow): 6:44 p.m. (00:43 UT Feb. 11)
Eclipse ends: 8:53 p.m. (2:53 UT Feb. 11)
The southern or bottom half of the moon is home to the pasty white lunar highlands, the first solid crust to form on the cooling moon 4.5 billion years ago. The northern half of the moon has more of the darker “seas”, areas that originally were huge impact basins that later filled with dark-colored lavas. At maximum eclipse, the northern or darker half of the moon will plow deepest into the penumbra, which should make the shading more dramatic than at other penumbral eclipses.
Try recording the event on your phone. Your best photo opportunity will be when the moon first comes up and the light from the lunar disk balances with the ambient light of twilight. Once the sky is dark, it’s more difficult to get a good photo without the phone camera completely overexposing the bright moon.
Here on Earth, the planet’s shadow can grow after sunset to cover the entire sky, but at the moon’s average distance of 239,000 miles, the combined penumbra and umbra span just 2.5° of sky or about the width of your thumb held at arm’s length. Stick out your thumb while watching the eclipse to get a feel for it.
I’m hopeful we’ll get a break in the forecasted clouds Friday evening as I, like you, face east after sunset into the shadow. In case of bad weather, astronomer Gianluca Masi will webcast the eclipse live starting 4:15 p.m. CST (22:15 UT). Clear skies and happy skywatching!
** Want to know more about eclipses and all the cool stuff you can see on the moon with just your naked eye? Pick up a copy of my recently published book, Night Sky with the Naked Eye, at Amazon or Barnes and Noble. It covers lots of different night sights — no equipment required!