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Longest partial lunar eclipse in 1,000 years coming Thursday night

November 17, 2021

By Fred Espenak

A deep partial lunar eclipse will darken the moon for much of the globe overnight on November 18 for North America. Most locations will see up to 97-percent of the moon slip into Earth’s shadow. North America has the best location to see the entirety of the eclipse.

This is an exceptionally deep partial eclipse with an umbral eclipse magnitude of 0.9742. In other words, 97-percent of the moon will be covered by Earth’s dark umbral shadow.

With a just thin sliver of the moon exposed to direct sun at maximum eclipse, the rest of the moon should take on the characteristically ruddy colors of a total lunar eclipse.

This eclipse occurs at the moon’s ascending node in Taurus. The moon will be placed near the famous Pleiades – aka the Seven Sisters – during the eclipse. Great photo opportunity!

The eclipse takes place 1.7 days before the moon reaches apogee at 2:14 a.m. Coordinated Universal Time (UTC) Sunday, November 21, its farthest point from Earth for this month.

For that reason, this is also the longest lunar eclipse in a span of some 1,000 years.

During a lunar eclipse, two shadows are cast. The dark inner part of Earth’s shadow
is called the umbra. The second is the penumbra. Illustration by NASA.
Viewers in North America and the Pacific Ocean, Alaska, eastern Australia, New Zealand and Japan will be able to see the entire partial lunar eclipse.

Observers in western Asia, Australia, and New Zealand miss the early stages of the eclipse because they occur before moonrise. Similarly, South America and Western Europe experience moonset before the eclipse ends. None of the eclipse is visible from Africa, the Middle East or western Asia.

At the instant of greatest eclipse (09:02:56 UTC) the moon lies at the zenith for a point in the Pacific Ocean east of the Hawaiian Islands. The moon’s southern limb lies 0.8 arc-minutes outside the edge of the umbral shadow.

For those in the Pacific time zone, the show will begin at around 10 p.m. Thursday when the penumbra first becomes visible. The eclipse begins at 11:18 p.m. and reaches maximum at 1:03 a.m. Friday.

The partial eclipse ends at 2:47 a.m. and the penumbra will last be visible at 4:06 a.m.

The partial lunar eclipse of November 19, 2021, is followed two weeks later by a total solar eclipse on December 4, sadly not visible in the United States.
A map of visibility for the November 18-19, 2021, partial lunar eclipse. The Americas are favored, but observers in northern Europe, eastern Asia, Australia and the Pacific will see it, too. The star marks the point where the maximally eclipsed moon will appear directly overhead. Image by Fred Espenak.

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