Not all lunar eclipses are created equal, and this Wednesday, Oct. 8, you’ll get the chance to see one of the rarest types, called a selenelion or horizontal eclipse. But you have to be quick, because you’ll only have between two and nine minutes to catch this crazy light trick.
Most of the time, a lunar eclipse will occur well before sunrise, but that won’t be the case on Wednesday morning. The Earth will pass between the sun and moon, eclipsing the moon in the process, which will begin at 6:25 a.m. EST and last through sunrise, but only on the east coast.
That means during a brief window, in this case between two and nine minutes, people on the east coast of the country will be able to see the sun rise and moon set at the exact same time. This rare event is referred to as a selenelion or horizontal eclipse.
There are plenty of times when both the sun and moon are visible during the day at other times of the year. But during a lunar eclipse the chance to see both the sun and moon simultaneously is extremely rare. This is because, geometrically speaking, this kind of phenomenon should not be possible.
During a lunar eclipse is one of the only times that the moon and sun are exactly 180 degrees apart on Earth’s sky, which means that right after the moon sets, the sun should rise, making it technically impossible to see both at once.
But a simple trick of the light changes everything and as a result crafty observers can see this wild, and otherwise impossible, event.
Observers in Australia, western Asia, islands in the Pacific Ocean, and much of North America will get the chance to observe this unusual eclipse.
Because Earth’s atmosphere refracts, or bends, light at a certain angle near the horizon, it creates an optical illusion that both the sun and moon appear slightly higher in the sky and therefore less than 180 degrees apart. As a result, we get a tiny window where we can see both celestial orbs simultaneously.
Unless you’re or atop a mountain or sailing in the middle of the ocean, however, you might be hard pressed to catch this trick of the light. You need to be in a spot where you can clearly see both the east and west horizons. But if you are in such a spot, you’ll catch an especially rare sight of a setting eclipsed moon with a rising sun.
Furthermore, we are in a rare series of lunar eclipses. This lunar eclipse is the second of a series of four consecutive total lunar eclipses. The first total lunar eclipse was April 15, 2014, and the next two will be on April 4 and September 28 of next year. This series of total lunar eclipses is rare and the next series of four consecutive total lunar eclipses will not occur until the year 2032.
Sky watchers in the USA will see the Moon turn a beautiful shade of celestial red and maybe turquoise, too, according to this video from Science@NASA. Watch to find out more about the eclipse:
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