It’s the first of two total lunar eclipses visible from the United States this year. The next is slated for the night of Nov. 7, and will favor parts of northwestern North America missing out on Sunday night’s show.
What is a total lunar eclipse?
Eclipses of all forms occur when one object blocks another. In the case of a total lunar eclipse, the Earth intercedes between the sun and the moon. You might expect that to prevent sunlight from reaching the moon, making it disappear, but that doesn’t happen. Instead, some sunlight skims around the periphery of Earth through our atmosphere and is scattered toward the moon.
For this to happen, the sun, Earth and moon all have to be in a line. That only happens during a full moon.
Total solar eclipseson the other hand, take place during new moons, when the moon slips between Earth and the sun. That extinguishes sunlight from reaching a narrow corridor of Earth, transforming day to night. Solar eclipses also allow the emergence of the sun’s milky white corona, or atmosphere, ordinarily outshone by blazing sunlight.
Solar and lunar eclipses come in pairs about two weeks apart; the most recent partial solar eclipse, on April 30, was visible from South America.
The total lunar eclipse will begin as an unremarkable “penumbral” lunar eclipse — a subtle darkening hardly perceptible to the untrained observer. That’s when the broadest, most diffuse part of the Earth’s shadows begins sweeping across the lunar surface from the bottom left to top right.
The partial phase of the eclipse will ensue, when the edge of the umbra, or darkest part of the Earth’s shadow, first makes contact with the moon. You’ll see a veil of darkness traverse the moon, its edge a gentle curve representing the shape of Earth. The shadow’s curve will be more gentle than that of the moon, since the Earth is larger.
Once the shadow fully swallows it, the moon will turn red. That’s because the only light reaching the moon is what streams through Earth’s atmosphere. Shorter wavelengths/higher frequencies of light are scattered away, leaving only the longer wavelengths, colored red, able to penetrate through the length of the atmosphere at a low angle of incidence. It’s the same premise that makes sunrises and sunsets red. Therefore, you’re seeing the light of ever simultaneous sunrise and sunset projected onto the moon.
Maximum eclipse comes when the moon is most firmly burrowed within Earth’s shadow, immersed in nothing but eerie red light. The color of a lunar eclipse actually varies depending on how polluted the atmosphere is; astronomers rate the tonal hues on the Danjon Scalefor which a zero corresponds to a hardly visible eclipse and a four represents a coppery-rust one. Volcanic eruptions and the presence of aerosols have been known to reduce the vibrancy of lunar eclipses.
All times provided are in Eastern time:
Begin penumbral eclipse: 9:32:05 p.m. Eastern time
Begin partial eclipse: 10:27:52 p.m. Eastern time
Begin totality: 11:29:03 p.m. Eastern time
Maximum eclipse: 12:11:28 a.m. Eastern time
End totality: 12:53:55 a.m. Eastern time
End partial eclipse: 1:55:07 a.m. Eastern time
End penumbral eclipse: 2:50:49 a.m. Eastern time
Note: For some on the West Coast, the moon won’t rise until totality is already underway. Moonrise in San Francisco, for example, is slated for 8:06 p.m. Pacific time, just 23 minutes before totality commences.
How special are total lunar eclipses?
Lunar eclipses aren’t nearly as special as total solar eclipses. Lunar eclipses can be visible from the entire night side of Earth, since the moon is visible from anywhere. Most places get one or two total lunar eclipses per year.
Total solar eclipses, on the other hand, are visible from a given location only once every 375 years on average. The path of totality may be a sliver hardly a mile wide, and the experience is surreal. The next that will be seen in the United States will be on Monday, April 8, 2024.
Patches of clouds will be scattered intermittently across the Eastern Seaboard, Intermountain West, Sierra Nevada and Pacific Northwest. The center of the country will see large expanses of clear skies favorable for viewing.
A more refined prediction will be made in the days ahead.