Saturday, December 10, 2011, will bring a spectacular and unusually rare, total lunar eclipse (start to finish photo gallery here) that will be visible in the United States, skies permitting. So, with this being such a rare and spectacular event, this one has an especially unique dimension to it: it shouldn’t even be able to happen at all.
While lunar eclipses, though rare, are nothing unusual in of themselves, this one that is to occur on Saturday is especially unusual in that this one will take the form of what is called a ‘selenehelion,’ or, in layman’s terms, an event where both the Sun and eclipsed Moon can be seen in the sky at the same exact time. Now, according to celestial geometry, this should be impossible as, at Full Moon, the Moon and Sun are exactly 180 degrees apart in the sky, meaning that, as the Moon sets, the Sun should rise. However, come Saturday morning, this apparent law of celestial mechanics is about to get broken, or is it?
First off, the Sun and Full Moon can be seen in the same sky at the same time. Why, you ask? It’s all about a trick of light.
When light reflected off of a celestial body comes to our eyes through the atmosphere, it refracts, or bends. The result: thanks to the refraction of light, we actually can see the Sun/Moon before it truly rises and, at the other end of the spectrum, we can see it for a few minutes after it has already set. Now, taking this knowledge, namely that we can see the Sun and Moon before they rise over/drop below the horizon, it all makes perfect sense in that, when the Sun is coming up and the Moon is full, exactly 180 degrees opposite the Sun, they will appear in the sky at the same time thanks to the refraction of light. This time, though, this unusual and obscure phenomenon will be showcased by a rusty red, eclipsed Moon.
Want to see a selenehelion for yourself? Well, at least in the Cleveland area (and the rest of the Eastern United States), you’re out of luck as no one in these time zones will get to see totality at all. However, should you live in the Great Plains of the Rocky Mountain states, you will see an eclipsed Moon setting just as the Sun rises, thus the rare, seemingly impossible selenehelion.
Want to see the eclipse? As always, be sure to check your local weather forecast or, even better, a nearby Clear Sky Clockas it will give hourly cloud forecasts. As for the Cleveland forecast, we won’t be able to see the totalitybut, things are looking pretty iffyfor anyone looking to see the dawn beginnings of the event, so cross your fingers for a few breaks in the clouds. For an even more up-to date, hour-by-hour weather forecast, check out the Cleveland Clear Sky Clock to see what the night will bring as the big event draws closer.
For more eclipse news:
Photograph it through a telescope
Photograph it with a dSLR
Photograph it with a cheap pocket cam
For more info:
Eclipse coming, get psyched!
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National Space News Examiner
Cleveland Photography Examiner
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