Diagram showing the conditions for super blood Moon' total lunar eclipse tomorrow night. (From WSJ, Jan. 18, p. A3)
The excitement is building and the whole astronomical community is readying itself for the only total lunar eclipse of the year tomorrow night. And it will also be a "Super Blood Wolf Moon". Why these terms? A 'blood Moon' because the lunar surface appears reddish or ocher on account of being seen through the Earth's atmosphere. Thus, we observe the Moon, say in partial eclipse phase, as seen in the photo below:
It is "super" in the sense of appearing larger than usual because of being much closer to the Earth, i.e. at its perigee point in orbit. This has the Moon at 223, 000 miles distant as opposed to 251,000 miles at it apogee or most distant point. The 'wolf Moon' just refers to a full Moon in January. Nevertheless, it appears some stuffed shirt astronomers are upset at the use of the phrase for this total lunar eclipse (WSJ, today, p. A1) But as Zoe Learner of Cornell aptly put it, she has no problem as long as there are no inaccuracies., to which I concur.
As readers will gather from this discussion, lunar eclipses - which are relatively common (70 or so a year)- only occur at the full Moon phase. The more detailed sketch below also helps to understand the stages of such eclipses:
Note the alignment (top) fixes the Sun at one end and the Moon at the other with Earth in between. The light from the Sun - on intersecting the Earth - produces a smaller, darker umbra and a lighter outer shadow cone called the penumbra. If the lunar transit is such that the Moon (as seen from Earth ) only passes through the penumbra, we have a partial lunar eclipse.
If, on the other hand, the Moon passes through the darker umbra, we have a total lunar eclipse and what is called a "blood Moon" because the lunar surface appears reddish or ocher on account of being seen through the Earth's atmosphere. Thus, we observe the Moon as seen in the photo.
Now here are the eclipse stage time, all in Eastern standard time, which should be converted to your local standard time:
9: 36 p.m. - Eclipse begins as Moon moves into the outer part of Earth's shadow (penumbra). The Moon appears slightly dim for about the next 37 minutes.
10:33 p.m. - Moon starts to pass into the inner, darker part of the Earth's shadow (the umbra). Moon will be seen to take on a darker hue.
11:41 pm.: Moon will be completely inside the Earth's central shadow, and take on the reddish hue seen in the photo. See also above diagram. This total phase will last until 12: 43 a.m. when the Moon retreats from the central shadow and its color gets progressively lighter.
We will be out observing with our small refracting telescope. The good thing about the timing here is the next day is a federal holiday, so the kids ought to he able to stay up to see this natural wonder. Much preferable to staring at cell phones!
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