How to shadow the lunar eclipse of Tuesday, April 15

 

 

An illustration of the phases of the upcoming eclipse. Courtesy Starry Night Software. Click illustration to enlarge.

An illustration of the phases of the upcoming eclipse. Courtesy Starry Night Software. Click illustration to enlarge.

By Claudio Veliz

From anywhere in the United States with clear skies, including Vermont, you will be able to enjoy a total lunar eclipse in the pre-dawn night of Tuesday, April 15, when the sun, Earth and moon align and Earth’s shadow fully covers the moon.

Eclipses come in two basic forms. Lunar eclipses, as will occur on the April 15, and solar eclipses, when the moon moves between the sun and Earth, casting its shadow on Earth’s surface.

Lunar eclipses are described by what part of Earth’s shadow the moon moves through in its orbit during the eclipse. The shadow has two parts: the umbra, which is the inner and much darker portion of the shadow, and the penumbra, or partial shadow, which is around the perimeter of the umbra, like a two-part bull’s eye.

The outer shadow, or penumbral passage, is a bit of a yawner. It’s like the quiet prelude to a symphony, and is barely visible unless you’re used to seeing these events.

The visual drama starts getting serious when the limb of the moon — the¬†edge of the moon’s visible surface — enters the umbra. First, it starts looking oddly gray-ish on the limb. Then it becomes distinctly darker and the climax arrives when the moon is fully enveloped in the umbra.

At this point the moon may become completely invisible. Or if the refracted light from all the Earth’s sunrises and sunsets converge on the moon just so, the moon’s disc will turn a bloody, coppery red. The actual appearance is unpredictable each time.

It lingers in this beautiful state for about an hour and a quarter before reversing the sequence and emerging back to being a brilliant, full moon.

So, when to look? This will be a very middle of the night affair, so you may want to go to bed early and set your alarms.

The moon enters the penumbral shadow shortly before 1 a.m. If you want to linger in bed a bit longer and just get up during the juicer bits, then the moon enters the umbral portion of the shadow about an hour later.

The disc of the moon will be in full umbral shadow at 3:06 a.m. and start to emerge from the umbra at 4:24 a.m. It finally leaves the umbra at 5:30 a.m. and the penumbra at 6:37 a.m.

If you rise and look for it in the early stages of the event, you’ll have no problem finding the moon about half way up in the southern sky. The latter stages of the eclipse will be seen as the moon sets in the west.

What if it’s cloudy, or your alarm fails you? Good news: this year and next there will be three more of these lunar eclipses, and so three more chances for the skies to be cloudy.

To learn more:

Claudio Veliz is an architect and astronomer based in Chester, Vt. He is also a member of the Southern Vermont Astronomy Group.

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