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| "Super blood wolf moon," the moon in total eclipse, January 20, 2019. |
Two days after the fact, the moon is now on its way through its waning gibbous phase, having reached full moon phase in the shadow of the earth on Sunday night, at the same time it reached the midpoint of a total lunar eclipse.
I was lucky to see the moon go through the penumbral (partial eclipse, partly in shadow) and then the first several minutes of the umbral (fully in the shadow, total eclipse) stages.
It was beautiful, especially through binoculars.
After that, from where I was looking near the shore of Hood Canal, the moon was covered by clouds.
Above is a picture of last night's super blood wolf moon that a person I know took and sent to an acquaintance, who shared it with me.
About the fancy name of this moon. The term "super" comes from astrology and just means the moon is near perigee, near the part of its elliptical orbit around earth where it comes closest to earth, so it looks a few percent larger than average. There is nothing all that super or unusual about it, except that only a few such full moons happen each year and it looks a little bit bigger than usual, though not so much bigger as to be obviously bigger to most people.
"Blood" is a slang word for the moon in earth's umbra and refers to the color of the moon when it is being totally eclipsed. In other words, “blood moon” derives from the color of the moon when it is completely in the shadow, or umbra, of earth. During total lunar eclipse, there is nowhere on the surface of the moon from which you could see the Sun, because the earth is obscuring the Sun entirely.
The moon takes on a reddish-dark-gray color when it is in total eclipse, and people emphasize the reddish aspect of the eclipsed moon's color by the word blood.
The red color is the color of sunlight that has passed through and back out of earth's atmosphere, around the rim of the earth, and been refracted (bent) into the shadow. He refraction (bending of the light path into the shadow) is due to the slower speed of sunlight as it travels through the air, slower than the speed of light in a vacuum.
Back to explaining the red color. The blue photons, because of their small wavelength relative to the size of typical gas molecules in the atmosphere, have been scattered off to the side a lot more than the red photons as the light passed through the air. That is why the sky is blue when you look up at it during the day (you're looking mostly at photons scattered to the side) and why sunrise, sunset, and the light refracted into earth's shadow, the unscattered sunlight, is red.
During total lunar eclipse, the light in earth's shadow is the light of sunset all around the rim of the earth, as seen from the moon. This reddish light reflects off the gray and white rocky surface of the moon and back to our eyes, giving the moon a "blood" color during total eclipse. More like dried blood.
A folk name for the full moon in January is wolf moon.
None of these are words defined or invented by astronomers, they are words from folklore and media hype, and they have some validity to their meaning.
Below is a sequence of photographs of the moon being eclipsed on Sunday. It was either taken by a friend of a friend of mine in Facebook.
The sequence does a nice job of showing how the moon went through the penumbral stage (partly in earth's shadow), then the umbral stage of the eclipse (the total eclipse state, fully in earth's shadow, when it turned a dark-gray shade of red), then through the penumbral stage again as it came out of total eclipse on the other side of the earth's shadow.
From the curvature of earth's shadow, you can tell the moon did not pass through the very center of earth's umbra, but along a pathway across the top half of earth's shadow.
This diagram below, from Sky & Telescope Magazine, shows what I mean (https://www.skyandtelescope.com/observing/solar-and-lunar-eclipses-in-2019/).
The diagram also shows why the top edge of the eclipsed moon was brighter than the rest of our satellite's orb during the eclipse.
The amount of sunlight that is is refracted by our 's atmosphere into earth's shadow is greater at the outer rim of the shadow, and declines towards the center.
The center of the umbra (center of the circular shadow) is the darkest part, with the lowest amount of sunlight refracted into the center.
At the mid-point of the eclipse sequence on Sunday night, the top of the moon was near the outer rim of the umbra, and so it was more lit up by sunlight refracted into the umbra. This is best shown in the eighth photo out of twelve in the sequence above (middle of the third row of photos).
This is also well displayed in the single, stand-alone photo up above.
At the mid-eclipse point, the bottom edge of the moon (or bottom-right edge, to be more specific), was nearest the center of the umbra. Hence, that edge of the moon was darkest.
This is represented by the point labeled "Mid-eclipse 5:12 UT" in the diagram below. (UT stands for Universal Time.)
Thus, even during a total lunar eclipse, the moon is not equally dusky across its entire face. The edge of the moon nearest the outer edge of earth's shadow is brighter, and the edge nearest the center of earth's shadow is darker.
What about you? Did you see it? Have you seen a lunar eclipse before?
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