A blood moon lunar eclipse brings a rare ‘selenelion’ on November 8th
Observers across the central and eastern United States and Canada should pay particular attention to the environment full moon On the morning of November 8, for that morning lunar eclipse it will still be ongoing.
An interesting observation to try that morning would be to watch the eclipsed moon set and the sun rise simultaneously. A little-used name for this effect is “selenelion,” a phenomenon that celestial geometry says cannot happen.
And indeed, during a lunar eclipse, the sun and the moon are exactly 180 degrees apart in the sky; so that in a perfect alignment such as this (called “syzygy”) such an observation would seem impossible. But remember that thanks to our atmosphere, the images of both the Sun and the Moon are apparently “raised” above the horizon by atmospheric refraction. This allows us to see the sun a few extra minutes before it actually rises and month a few extra minutes after it actually sets.
Joe Rao is a veteran meteorologist and eclipse chaser who also serves as an instructor and visiting lecturer at New York’s Hayden Planetarium.
As a result of this atmospheric trick, for many localities east of the Mississippi, there will be an opportunity to observe this unusual sight firsthand with the November shadow event; a brief window of approximately 4 to 9 minutes (depending on your location) in which it will be possible to simultaneously see the sun rising in the east while the eclipsed full Moon sets in the west.
Regions of visibility
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From Newfoundland, the onset of partial phases begins about 80 minutes before moonset; a growing cap of darkness will appear in the upper left of the moon as the dawn sky clears, and the moon slips into total eclipse less than a quarter of an hour before it sets. Similarly, further west and south over Nova Scotia and along the immediate Atlantic coast, the Moon will set fully immersed in Earth‘s shadow. See the table (below) for specific details for twenty selected locations in the US and Canada.
|Location||Time zone||Sunrise||Moonset||Moonset Mag*|
|St. John’s, NF||NST||6:55 am||6:59 am||In total|
|Halifax, NS||AST||7:02||7:06||In total|
|Boston, MA||IS||6:26||6:32||In total|
|New York, NY||IS||6:35||6:41||In total|
|Miami, FL||IS||6:34||6:38||In total|
|New Orleans, LA||CST||6:20||6:26||0.34|
|St. Louis, MO||CST||6:35||6:44||0.07|
*Moonset Mag: The fraction of the Moon’s diameter within the Earth’s umbral shadow at Moonset rounded to the nearest percent.
Now you see it. . . Not now?
Then again, spotting selenelli can be a troublesome feat. Thirty-three years ago, in the August 1989 issue of Sky & Telescope magazine, Bradley Schaefer, an astronomer who has extensively studied the visibility of the moon when it is low in the sky, noted that the full moon only becomes visible when it is about 2- degrees higher and the sun is about 2 degrees below the horizon.
So, depending on the clarity of your sky, you may have about 10 to 15 minutes before sunrise for the sky to still be dark enough and the moon to be high enough above any horizon haze to be seen clearly. And note that this only applies to the non-eclipse part of the month. However, you may be able to mitigate the effects of brighter skies somewhat with binoculars or a telescope.
If the moon is completely eclipsed before sunrise, you’ll probably need to scan the western horizon with binoculars as dusk brightens to still detect some semblance of the moon, somewhat like a very dim and eerily lit colorful softball.
An unusual moonset
For those parts of the United States and Canada several hundred miles inland from the East Coast, a slightly later Moonrise from the umbra should be well seen. A low, partially eclipsed Moon in deep blue twilight should offer a wide variety of interesting scenic opportunities for artists and astrophotographers alike. From Buffalo and Pittsburgh and pointing south through the eastern Ohio Valley and into the Piedmont to the Florida Panhandle, an unusual-looking waxing crescent moon looks set to appear with its tips pointing down beyond the western horizon.
Farther west, across the central Great Lakes, down the deep south to the Gulf of Mexico, the moon will appear to have a shadow carved into its lower right side.
Going even further west, the Moon will set “full” but diligent observers from much of Wisconsin, Iowa, western Missouri, eastern Oklahoma, and central Texas may still be able to detect a faint spot in the penumbra at the lower right of the moon if the west horizon without fog.
Joe Rao serves as an instructor and visiting lecturer in New York Hayden Planetarium (opens in new tab). He writes about astronomy for Natural history magazine (opens in new tab)the Agricultural Almanac (opens in new tab) and other publications. Follow us on Twitter @Spacedotcom (opens in new tab) and further Facebook (opens in new tab).
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