Double_Cluster.jpg

An image of the Double Cluster, which can be viewed with the naked eye, even in moderately dark conditions. Courtesy of Wikipedia

If you stay up late on Nov. 18 you will be treated to an almost total lunar eclipse at about 2 a.m. MT on Nov. 19. Only a thin sliver of the moon will still be exposed to sunlight while the rest of the moon will look dark and can vary in color from almost invisible, gray, brown, red, rust, orange or copper.

Our moon does not generate its own light. The moonlight we see from Earth is actually sunlight reflecting off the moon. If you were out in space and could look down on the moon, Earth and sun you would see that one half of the moon is lit up by the sun at all times. From Earth, the only time we see the half of the Moon that is completely lit up is during a full moon, which occurs every month when the moon is directly opposite the dun as seen from Earth. Usually when we have a full moon, the moon is either above or below the plane of the Earth’s orbit, so no eclipse occurs.

However occasionally the full moon moves directly into our Earth’s plane and will pass through the Earth’s shadow. Again, if you could see this from space, the Earth’s shadow appears as a cone shaped object which blocks most of the sunlight from lighting up the moon and we are treated to a lunar eclipse on Earth. The November 18-19 lunar eclipse is visible to anyone who can see the moon that night and is visible from all of North America. Observing a lunar eclipse requires no optical aids and is completely safe to view directly.

During a total lunar eclipse the moon never completely disappears but always turns some unpredictable shade of reddish copper orange. This happens because the red rays of sunlight are always bent by our Earth’s atmosphere into our Earth’s shadow, filling it with a faint reddish copper orange light. During a total lunar eclipse the reddish orange color you see is actually light from all the sunrises and sunsets around the world being refracted and bent into our Earth’s shadow then reflected onto the moon.

Taking a closer look at the Earth’s shadow cone, there are two distinct parts to it, a pale outer shadow called the penumbra and a smaller dark inner shadow called the umbra. The penumbral phase of the eclipse is never very noticeable but starts in Cheyenne on Thursday evening at 11:02 pm MT and goes until 12:18 a.m. MT Friday morning. The darker umbral eclipse starts at 12:18 a.m. MT when as the minutes go by you can actually see the umbra, our Earth’s curved shadow slowly creep across the moon and gradually darkens it enough to change color. While this won’t be a total lunar eclipse the moon will be almost 97% eclipsed reaching maximum eclipse at 2:02 a.m. MT.

After the eclipse reaches maximum you can watch the whole process slowly reverse itself until the umbral shadow leaves the moon at 3:47 am MT. No one can predict how dark or what color an eclipsed moon will be, but it’s always fun to watch. Clouds, water droplets, dust, smoke and volcanic ash can all determine how dark the eclipsed moon will be and, as mentioned above, what color it will be. Since this isn’t a total eclipse, the darkened moon will still be brighter than Venus but certainly not as bright as a full moon. The eclipsed Moon is in Taurus that evening and will be near Pleiades; a beautiful tiny cluster of stars that resembles a tiny dipper. A full moon can dim the surrounding sky so at the beginning of the eclipse Pleiades won’t be very obvious; as the moon continues to darken during the eclipse the star cluster will be more obvious.

The moon that night will be smaller than average because it is about 2 days away from apogee, which is its farthest point from Earth during its monthly cycle. Being farther from the Earth also means it takes the moon a longer time to pass through the Earth’s shadow; this eclipse will take 6 hours from first penumbral contact until it moves completely out of the Earth’s shadow. The Earth will spend 3.5 hours in the darker umbral shadow.

For precise timing for your location please check https://www.timeanddate.com/eclipse/lunar/2021-november-19.

This is a monthly article provided by the Cheyenne Astronomical Society (CAS). Marcy Curran has been the editor of the Cheyenne Astronomical Society’s newsletter since 1986 and taught astronomy at LCCC from 1992-2013. For further information about the CAS, visit our website at killerrabbit.co.

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