We have an eclipse of the full Moon scheduled for Friday night, February 10th, but it’s not likely that the astronomical community at large is going to get very excited about it. Why? Because this eclipse is actually a “penumbral” lunar eclipse.
The Earth casts not one, but two types of shadows out into space: an umbra, the shadow directly around it, and a penumbra (see graphic, below). When the Moon passes into the umbra, we can readily see a dark and very distinct outline of the Earth’s circular shadow cast upon Moon’s disk. The penumbra, on the other hand, casts a much fainter and far less distinct shadow, which is far more difficult to perceive and as such might not immediately catch your eye.
In a total lunar eclipse, the Earth’s shadow, called the umbra, falls over the Moon, and at the mid point of the eclipse, the entire Moon is in the Earth’s shadow, causing the Moon to appear red.
In a partial lunar eclipse, the umbra obscures only part of the Moon.
In a penumbral lunar eclipse, the Moon is only passing through the penumbral shadow.
On Friday, February 10th, the Moon will start to enter the penumbral shadow at 5:34 p.m. EST. Absolutely nothing unusual will be noticed on the lunar disk at that time. But the darkest phase of the eclipse is scheduled for 7:43 p.m. At that moment the percentage of the Moon’s diameter that is within the faint penumbral shadow – will equal 98.8 percent. Perhaps for a half hour before and after this time, the upper portion of the Moon should appear lightly “smudged” or shaded, especially through binoculars and low-power telescopes.
Folks who live in the Pacific Time Zone, however, may miss out entirely, since the Moon will be below the horizon during the darkest phase of the eclipse. But if you live out west, don’t fret over this. After all, as most eclipses go, this is a rather underwhelming event.
The eclipse you will definitely get excited about is the Great American Solar Eclipse, a total solar eclipse, occurring on August 21, 2017! Read more about it here.