Including phases where the moon is partially masked, the event will last nearly four hours total.
For any stargazers out there feeling eclipse withdrawals, the universe has good news: the longest lunar eclipse of the 21st century will occur in just a few weeks, on the evening of July 27. The bad news? If you’re reading this within U.S. borders, you won’t be able to watch from home.
This eclipse will be completely visible in Eastern Africa and Central Asia from 3:30 p.m. to 5:13 p.m. EDT, while viewers in Western Africa, Eastern Asia, South America, Europe, and Australia will catch a partial glimpse, according to Temi Adebowale at Popular Mechanics. Including phases where the moon is partially masked, the event will last nearly four hours total.
Unlike solar eclipses like last year’s much-hyped summer spectacular, in which the moon passes between the Earth and the sun, blocking the sun from view, a lunar eclipse occurs when the Earth passes between the moon and the sun, obscuring the moon from the sun’s illumination. So, rather than darkened skies, viewers will be treated to a ruddy red visage that’s often dubbed a “blood moon” (though the most finicky reserve this term for a series of four consecutive lunar eclipses).
Eerie as it may be, the moon’s face appears rouged for the same reason the sky looks blue to our eyes. Though concealed by the sun, the moon is still flecked with a few stray particles of light filtered through Earth’s atmosphere. Air on Earth scatters shorter-wavelength light, including most of the blues and greens (which trickle down to us on the planet’s surface), leaving the longer reds to spotlight the moon.
The reason this lunar eclipse will be a particularly long one is because the moon will be passing almost directly through the central part of Earth’s shadow, while the moon is at a particularly distant point from Earth in its monthly orbit. During the summer months, Earth also swings out to its furthest distance from the sun, allowing it to cast a particularly long shadow.
These three factors are what have lengthened the duration of July’s eclipse to 1 hour and 43 minutes, which NASA estimates will be the longest total lunar eclipse of the 21st century. To put this in perspective, it falls just four minutes shy of the longest lunar eclipse possible for Earth’s most faithful satellite.