104 minutes. That's the length of the longest lunar totality of the 21st century. And it happens Friday, July 27th, when the Moon creeps into Earth's umbra like some thief in the night. If my dad were still alive, he'd probably watch for 10 minutes and be done with it. "Enough's enough," he'd say. But for his son and fellow skywatchers, staring down the length of Earth's shadow is never a waste of time.
A total lunar eclipse occurs during a full Moon when the Sun, Earth, and Moon line up exactly in that order. Light from the Sun passes through the Earth’s atmosphere, which refracts the red and orange colors into the umbra to tint the Moon. The outer part of Earth's shadow, called the penumbra, is only partially dark because it's a mixture of shadow and sunlight. It's visible as a gray smudge on one side of the lunar disk starting about 20 minutes into penumbral eclipse.
Starry Night with additions by the author
2018 began with a total lunar eclipse on January 31st nicely split between Eastern and Western Hemispheres. Friday's eclipse is primarily an Eastern Hemisphere affair, visible from Europe, Africa, Asia, Australia, and parts of South America . Unlike a total solar eclipse, a total lunar is visible across half the planet wherever the Moon is up in the sky. Just wish my half of the planet was included!
The author photographing the total eclipse over the Duluth, Minnesota, skyline at dawn on January 31, 2018. A low Moon makes for scenic sweetness.
Mike Sangster
From far western Europe, the Moon rises in total eclipse around sunset and will be difficult to see at first in a twilight sky. As darkness deepens, contrast will improve, and the Moon will become a stunning sight against the deepening blue. Have your camera ready to capture a scene that includes the local skyline or a special landmark alongside our colorful satellite.
For a complete guide to lunar eclipse photography visit Fred Espenak's site MrEclipse.com. A digital SLR camera is best, but even mobile phones do a surprisingly good job. They work best in early to mid-twilight when moonlight is balanced with skylight in a deep blue sky, and you can still clearly see the landscape.
This map shows where the eclipse will be visible either in full or in part.
Fred Espenak
The further east you go, the more of the eclipse you'll see with the Moon higher up in a darker sky. The entire event — from the first hint of penumbral darkening to the last shadowy stain — will be observable from the eastern half of Africa, Turkey, the seven "Stan" countries, India, and Madagascar.
A unique set of circumstances brands this eclipse with the longest totality of any total lunar eclipse for the rest of the century — 1 hour 44 minutes, or 27 minutes longer than January's eclipse. Though still 2 minutes shy of the July 16, 2000, eclipse, that time will hold until June 9, 2123, when totality clocks in at 1 hour 46 minutes.
The Moon's central passage through the Earth's umbra ensures a longer-than-normal totality Friday. UT times are shown for the various phases of the eclipse. To convert UT to your time zone, use this handy converter.
So what makes Friday's eclipse so long?
First, the Moon crosses centrally through the umbra. The closer to a perfect bull's-eye, the longer the totality. Friday's Moon passes just a fraction north of center. Second, the farther the Moon is from Earth, the slower it moves. And the slower it moves, the more time it takes to cross the umbra. In a fortunate coincidence, lunar apogee (greatest distance from Earth) occurs on the very day of the eclipse. Third, Earth reached its greatest distance from the Sun or aphelion on July 6th. The farther a planet orbits from the Sun, the greater the diameter of its umbral cone and the more time it takes the Moon to ford it.
Mars and the Buck Moon will be in conjunction Friday evening. They'll also both be in "full" phase and at opposition.
Stellarium
Add 'em up and you've got a memorable eclipse. But wait, there's more! The full Moon joins the planet Mars which reaches opposition the very same night, shining a brilliant magnitude –2.8 or better because of the current dust storm.
Now, it's one thing to see a bright Mars and another to see the Moon in totality, but the sight of the two ruddy bodies rising together just ~6° apart should be nothing short of amazing. Will someone fall for the Mars hoax and mistake the Moon for Mars as one reader suggested? I try to imagine what special significance our distant ancestors might have read into this rare pairing of colorful orbs. An omen of war maybe?
This simulation shows how the Earth might look from the mid-northern latitudes of the Moon during Friday's lunar eclipse. The landscape is bathed in sunset colors from sunlight refracted by Earth's atmosphere. Stellarium with additions by the author
There's nothing so dreamy, so 3D as seeing the Moon soaked in blood orange sunlight while surrounded by dozens of stars during totality. Robbed of its radiance, the full Moon stands on par with the stars. And that color! Sunlight seeping around the circumference of the Earth and refracted by the atmosphere sheds all its colors but the warm ones. These beam to the Moon and paint it with the light of countless sunrises and sunsets. If we could stand on the lunar surface during totality we'd look back to see the big, black disk of Earth, its edge vibrant red, slowly cover the Sun in a total solar eclipse.
The stars returned in full force when the Moon (lower left) was totally eclipsed on September 27, 2015.
Bob King
A total lunar eclipse is perfectly safe to look at and offers different viewing experiences depending on your instrument — naked-eye, binoculars, or a telescope. Have all three on hand! I enjoy watching the shadow slowly cover the disk through the scope but also pay attention to the first penumbral darkening and later, the first hint of umbral red, with just my eyeballs. Seeing the stars and Milky Way return as the Moon treads deeper into the umbra borders on the spiritual and remains a favorite aspect of eclipse-watching. That's why I recommend viewing the event from a dark-sky site.
Other observers use total eclipses to watch occultations of fainter stars that would otherwise be impossible to see in the glare of the full Moon. Dozens of stars in Capricornus will be occulted Friday night, with 5.9-magnitude Omicron (ο) Capricorni the brightest. For details, check out this sitecreated by David Dunham and Eberhard Riedel with the International Occultation Timing Association(IOTA).
Eclipse aficionados in the Western Hemisphere and those socked in with clouds in the Eastern can still watch the eclipse via live streaming thanks to the efforts of Italian astrophysicist Gianluca Masi on his Virtual Telescope website and the folks at Bareket Observatory in Israel. Masi goes live starting at 18:30 UT on July 27th from the Roman Forum on Palatine Hill in Rome. Baraket starts at the same time and will stream for 5 hours. A reminder — those times translate to Friday mid-afternoon / early evening for the Americas.
The Danjon Scale is used to estimate the color of the totally-eclipsed Moon. Astronomers and climatologists use that information to determine how clean or “dirty” the stratosphere is.
Alexandre Amorim
Would you like to do some easy science during the eclipse? Using just your eyes, you can estimate the brightness of the fully-eclipsed Moon during totality. Astronomers rate lunar brightness and color using the Danjon Scale, numbered from 0 (a dark, brown-red eclipse) to 4 (a coppery-yellow eclipse).
Danjon Scale
L=0: Very dark eclipse. Moon almost invisible, especially at mid-totality.
L=1: Dark Eclipse, gray or brownish in coloration. Details distinguishable only with difficulty.
L=2: Deep red or rust-colored eclipse. Very dark central shadow, while outer edge of umbra is relatively bright.
L=3: Brick-red eclipse. Umbral shadow usually has a bright or yellow rim.
L=4: Very bright copper-red or orange eclipse. Umbral shadow has a bluish, very bright rim.
Key in the Danjon scale on your cell phone and compare it to the Moon, then share your L-number estimate with me and other readers in the Comments area below. This seemingly simple exercise can reveal much about the state of the atmosphere, including contributions by volcanoes and forest fires to darker eclipses.
The next total lunar eclipse swings back to the western hemisphere on the night of January 20–21 with a brief, 62-minute-long totality. I suspect few will complain about its short duration given the time of year!