Deep Penumbral Lunar Eclipse – Friday, February 10, 2017

The Moon is Full on Friday, February 10, but that’s not all.  It will plunge deeply into the penumbral shadow of the Earth, not quite touching the umbral shadow.  The penumbral shadow is the part of the Earth’s shadow where you would see the Earth partially eclipsing the Sun.  Normally, penumbral lunar eclipses are no big deal, as they are very difficult or impossible to discern, but this time you should be able to see a noticeable darkening of the full moon from left to right as the eclipse progresses towards maximum penumbral shading, and then brightening from lower right to upper left as the Moon exits the Earth’s penumbral shadow, as shown in this video.  Of course, how much of this you will be able to see will depend on both your local moonrise and when evening twilight ends.

Here are local circumstances for Dodgeville, Wisconsin:

Event Time Moon Altitude
Penumbral Eclipse Begins 4:34:14 p.m. below horizon
Penumbral Eclipse First Visible? 5:14 p.m.? below horizon
Moonrise 5:21:03 p.m. 0° @ 72° (ENE)
Sunset 5:25:43 p.m.
Civil Twilight Ends 5:55:09 p.m.
Nautical Twilight Ends 6:28:36 p.m. 11°
Maximum Penumbral Shading 6:43:54 p.m. 13°
“Dark Enough” 6:45:07 p.m. 14°
Astronomical Twilight Ends 7:01:33 p.m. 16°
Penumbral Eclipse Last Visible? 8:14 p.m.? 29°
Penumbral Eclipse Ends 8:53:29 p.m. 36°

For those of us in SW Wisconsin, I wouldn’t bother looking much before 6:30 p.m., because evening twilight is likely to be too bright.  The best time to look will probably be at 6:43 p.m., just a little over a minute before twilight ceases to become any real concern1.  Evening twilight officially ends at 7:01 p.m., and you will probably notice some shading on the Moon until about 8:14 p.m.

The Moon will be inching closer towards Regulus during the penumbral eclipse (and, in fact, all night long), so watch for that.

For the record, a penumbral eclipse this deep (when there wasn’t also a partial or total lunar eclipse) hasn’t happened since March 14, 2006 (which was even deeper), and won’t happen again until January 10, 2085, though we need only wait until January 31, 2018 and January 20, 2019 for the next two lunar eclipses and they will both be total lunar eclipses—far more impressive than any penumbral lunar eclipse could ever be.  We’ll be seeing only the beginning partial phases of the 2018 eclipse here because the eclipsed moon will be setting during bright morning twilight.  Fortunately, we’ll have a front-row seat to the entire 2019 eclipse as all of it will occur high in the sky after dark, with totality ending conveniently before midnight.

1My late friend Joe Eitter (1942-2014), who was the observatory manager at Iowa State University’s Erwin W. Fick Observatory during its entire existence, used to say that by the time the Sun got down to 15° below the horizon, it is “dark enough”.

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