A tetrad of Lunar eclipses

For people today in the United States, an extraordinary series of lunar eclipses is about to commence. The action begins on April 15th when the complete Moon passes via the amber shadow of Earth, producing a midnight eclipse visible across North America....

A tetrad of Lunar eclipses

For people today in the United States, an extraordinary series of lunar eclipses is about to commence.

The action begins on April 15th when the complete Moon passes via the amber shadow of Earth, producing a midnight eclipse visible across North America. So starts a lunar eclipse tetrad—a series of 4 consecutive total eclipses occurring at approximately six month intervals. The total eclipse of April 15, 2014, will be followed by one more on Oct. eight, 2014, and a further on April 4, 2015, and yet another on Sept. 28 2015.

"The most exceptional issue about the 2014-2015 tetrad is that all of them are visible for all or parts of the USA," says longtime NASA eclipse professional Fred Espenak.

On typical, lunar eclipses occur about twice a year, but not all of them are total. There are 3 kinds:

A penumbral eclipse is when the Moon passes by way of the pale outskirts of Earth's shadow. It really is so subtle, sky watchers often never notice an eclipse is underway.

A partial eclipse is far more dramatic. The Moon dips into the core of Earth's shadow, but not all the way, so only a fraction of Moon is darkened.

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A total eclipse, when the whole Moon is shadowed, is finest of all. The face of the Moon turns sunset-red for up to an hour or more as the eclipse gradually unfolds.

Generally, lunar eclipses come in no particular order. A partial can be followed by a total, followed by a penumbral, and so on. Something goes. Sometimes, though, the sequence is extra orderly. When 4 consecutive lunar eclipses are all total, the series is named a tetrad.

"During the 21st century, there are 9 sets of tetrads, so I would describe tetrads as a frequent occurrence in the present pattern of lunar eclipses," says Espenak. "But this has not generally been the case. During the three hundred year interval from 1600 to 1900, for instance, there have been no tetrads at all."

The April 15th eclipse begins at two AM Eastern time when the edge of the Moon initially enters the amber core of Earth's shadow. Totality occurs through a 78 minute interval beginning about 3 o'clock in the morning on the east coast, midnight on the west coast. Climate permitting, the red Moon will be effortless to see across the entirety of North America.

Why red?

A rapid trip to the Moon provides the answer: Consider yourself standing on a dusty lunar plain seeking up at the sky. Overhead hangs Earth, nightside down, totally hiding the sun behind it. The eclipse is underway.

You could possibly count on Earth observed in this way to be utterly dark, but it is not. The rim of the planet is on fire! As you scan your eye about Earth's circumference, you're seeing just about every sunrise and just about every sunset in the globe, all of them, all at as soon as. This remarkable light beams into the heart of Earth's shadow, filling it with a coppery glow and transforming the Moon into a excellent red orb.

Mark your calendar for April 15th and let the tetrad start.

Read More: Phys

28 March 2014 Friday 10:31
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