At 10:47 p.m. Sunday, skywatchers will witness a supermoon in total lunar eclipse, a rare event in which the normally bright disc will appear to become a reddish sphere. Weather permitting, of course.

The celestial extravaganza is the result of a supermoon – a term for when the moon, in its elliptical orbit, reaches the point where it’s closest to Earth – at the same time it passes completely through the Earth’s shadow.

Take a good look. That combination has occurred only five times since 1900 and won’t happen again until 2033.

It’s the kind of celestial event that can leave astronomers like Edward Gleason giddy. Gleason, manager of the University of Southern Maine’s Southworth Planetarium and staff astronomer, said the total lunar eclipse is especially cool, both aesthetically and analytically.

Visually, the moon will appear a reddish version of its three-dimensional self. That’s because the light it’s reflecting is not the direct white light of the sun, but red light that has funneled through the Earth’s atmosphere, Gleason said.

Because the moon is in perigee, it will appear 14 percent larger than when it’s at its most distant.

Skywatchers can camp out early if they want to see a partial lunar eclipse, which will begin at 8 p.m. in the United States.

The full eclipse, which will be visible in much of the world, is a huge deal for astronomy clubs.

David Clark of Stockton Springs, a physicist at the University of Maine in Orono and a member of the Penobscot Valley Star Gazers, says it’s a big event.

“We’re having a public star party at the Bangor Municipal Golf Course,” Clark said. “We’re basically going to be putting our telescopes on the moon for when the moon moves into the darkest shadow, the umbral phase.”

Clark said that beyond the sheer coolness of the eclipse, the event provides great viewing of the features on the moon, which are mapped like an atlas.

“It’s always great to see shadows move across the moon. You get to see the depth sometimes, the height of a mountain,” he said.

PREDICTING ECLIPSES WITH CERTAINTY

According to NASA, the event will be visible in North and South America, Europe, Africa, parts of West Asia and the eastern Pacific.

The event also is remarkable because of the precision with which astronomers can predict it.

“This just shows the power of astronomical mathematics,” Gleason said, his voice picking up pace. “We can time it and we know how long it will last. It’s always exciting to see all those elements come together.”

The partial eclipse will begin at 9:07 p.m. EDT. The total eclipse will start at 10:11 p.m. and end at 11:23 p.m. The center of the moon will be at its closest to the center of the Earth’s shadow at 8.8 seconds after 10:47 p.m.

According to Gleason, that certitude comes courtesy of a long line of astronomical geniuses, from Johannes Kepler and his laws of planetary motion to Jean Meeus’ studies in celestial mechanics. NASA’s Fred Espenak, an astrophysicist, developed sophisticated computer programs for predicting eclipses.

“We are the beneficiaries of their labors – significant, tedious, mind-numbing labors,” Gleason said. “Now, we will tell you what’s going to happen centuries in the future, far beyond our lifetimes.”

Sunday’s full moon also is called a harvest moon because it falls closest to the autumnal equinox. It also is considered a blood moon because it is the final total eclipse of the moon in a group of four, called a tetrad.

The next total lunar eclipse, when the moon is not at perigee, will be Jan. 20, 2019.

VISIBILITY FORECAST ‘PRETTY GOOD’

One aspect that all those celestial equations can’t predict, however, is how the moon will look during the total lunar eclipse. That depends on what the red light waves are hitting as they pass through the atmosphere. The moon could appear red, brown or gray.

Another terrestrial uncertainty that will greatly affect the moon’s appearance is good old, tough-to-predict weather.

“We’re thinking Sunday night might be pretty good to see the eclipse, as far as the sky cover goes,” said Michael Cempa at the National Weather Service in Gray. “One thing we’re kind of watching is a little bit of flow turning onshore and getting some lower clouds in at the coast. For now, it looks pretty good.”

David Hench can be contacted at 791-6327 or at:

[email protected]

Twitter: Mainehenchman

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