​Lunar Eclipse: Blood Moon Begins Tetrad

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Aug, 10, 2014 | 2:07 PM

A total lunar eclipse is coming, marking four during the next 18 months, beginning with one called a “blood moon” on April 15. The Tax Day eclipse has skywatchers in the United States talking.

The moon is about to shine red during the event, which will occur for about 78 minutes around 3 a.m. EDT (0600 GMT).

Lunar Tetrad

The total lunar eclipse “tetrad” will then continue with eclipses of the moon on Oct. 8, 2014, April 4, 2021 and Sept. 28, 2015.

“The most unique thing about the 2014-2015 tetrad is that all of them are visible for all or parts of the USA,” Fred Espenak, a NASA astrophysicist and eclipse specialist, said in a statement.

Tuesday’s total lunar eclipse, for example, will be visible from most of North America, as well as parts of South America and Alaska, weather permitting.

Last week, rumors swirled online suggesting a link between the total lunar eclipse tetrad and biblical prophesies of the apocalypse because it would bring about “four blood moons.” The theory was published in a book entitled “Four Blood Moons” by John Hagee in 2013.

Eclipse Patterns

Tetrads of moon eclipses are not super-rare, and do show a pattern.

“During the 21st century, there are nine sets of tetrads, so I would describe tetrads as a frequent occurrence in the current pattern of lunar eclipses,” Espenak said. “But this has not always been the case. During the 300-year interval from 1600 to 1900, for instance, there were no tetrads at all.”

As for the why the moon turns red during the eclipse, this is because it reflects sunsets and sunrises happening all around the world as the sun shines through the Earth’s atmosphere. This can turn the moon a dusky red color, sometimes even resembling the color of blood.

Lunar eclipses occur during full moons, when the moon passes behind the Earth, with respect to the sun. The alignment can either completely obscure the moon with Earth’s shadow (a total lunar eclipse), or partly covers the moon (a partial eclipse).

Because the moon’s orbit is tilted, it does not align perfectly every month, lunar eclipses typically occur about twice a year, but they usually come in different flavors. For example, a total eclipse could be followed by a partial eclipse, and then followed by a penumbral eclipse — an event in which the moon just skirts through the outer edge of Earth’s shadow.

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