How to Watch the Longest Partial Lunar Eclipse in 580 Years

Sky nerds are in for a treat this Thursday night or Friday morning.

The Earth will witness the longest partial lunar eclipse in 580 years, with the event set to last a full 3 hours, 28 minutes and 23 seconds, according to NASA.

“There hasn’t been a longer partial lunar eclipse since February 18, 1440 (3 hours, 28 minutes, 46 seconds) and it will remain the longest partial lunar eclipse for 648 years until February 8, 2669 (3 hours, 30 minutes, and 2 seconds),” NASA wrote.

Movie of the "NEAR TOTAL ECLIPSE." LONGEST PARTIAL LUNAR ECLIPSE in 580 years occurs on morning of November 19th. 1st parts of the eclipse begin at 1:02AM EST. Max eclipse occurs at 4:02 AM when 97% of MOON in darkest part of Earth's shadow. pic.twitter.com/2HwPpqPbbd

— Holcomb Observatory (@holcombobserv) November 13, 2021

A lunar eclipse occurs when the moon, sun and Earth all align so that the moon is covered by Earth’s shadow. In a total lunar eclipse, the moon passes entirely into the darkest part of Earth’s shadow, called the umbra. Tonight and this morning’s event will be an “almost total” lunar eclipse, which means that up to 99.1 percent of the moon’s disk will pass into the umbra.

The eclipse will be so long for two reasons.

1. The moon is currently close to the farthest point from the Earth in its orbit, which means it will be travelling more slowly.
2. The moon will spend more time in Earth’s shadow than it normally would during a partial lunar eclipse because this eclipse is “near total.”

During an eclipse, the moon doesn’t disappear. Instead, Earth’s atmosphere paints it in a reddish tone as it scatters the sun’s light onto the moon, NBC News explained.

This partial eclipse will be visible from North America, South America, Eastern Asia, Australia and the Pacific Ocean, as long as the skies are clear. The eclipse will come in two phases, CNN reported: the penumbral and umbral phases. The penumbral phase occurs when the moon enters the Earth’s outer shadow, or penumbra, and lasts six hours, while the umbral phase occurs when the moon enters the umbra and lasts 3.5 hours.

For North American viewers, the penumbral phase will begin at 1:02 a.m. Friday morning Eastern Time and 10:02 p.m. Pacific Time Thursday night, NASA said. This effect is more subtle, however. The show really begins with the start of the umbral phase at 2:19 a.m. Eastern, and the eclipse will peak at 4:03 a.m. Eastern, which is the best time to see the reddish color.

“The Moon will be in Taurus and pleasingly placed some 6° — approximately the width of three fingers held together at arm’s length — lower left of the pretty Pleiades open star cluster at the time of maximum eclipse,” Sky & Telescope observing editor Diana Hannikainen said. “This should provide great opportunities for some fun photos.”

If you want to know exactly when to watch for the eclipse where you are, you can check timeanddate.com.