Red Moon Meets Red Planet in Longest Total Lunar Eclipse of the Century

Not only will the Moon will be totally eclipsed this Friday, but Mars will be at opposition and shine in tandem with the red Moon all night! (Scroll down for online watching opportunities!)

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.

Just going through phases

During a lunar eclipse, Earth's shadow envelops the Moon, as shown in this sequence taken through a small telescope on September 27, 2015.
Jamie Cooper

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.

How lunar eclipses happen

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!

Moon meets Duluth

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.

Where to go to see the eclipse

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.

Bulls-eye!

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.

Moon hoax for real?

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?

Astronaut view

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.

Moon and Milky Way

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 site created by David Dunham and Eberhard Riedel with the International Occultation Timing Association (IOTA).

Watch Online!

Gianluca Masi

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.

Other webcasts include those offered by HESS, NamibiaSlooh, and Urania.

Eclipse Citizen Science

Eclipse experiment

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!

 

 

 

 

19 thoughts on “Red Moon Meets Red Planet in Longest Total Lunar Eclipse of the Century

  1. Robert-CaseyRobert-Casey

    I won’t see this one, as I’m the USA, but I do remember a deep lunar eclipse back in 1992 or so. I was working overtime at work that night, and a co-worker and myself went to take a look at the eclipsed Moon. We couldn’t find the moon, as it was all black. In a sense we did witness the eclipse. We “saw” a black Moon against a black light polluted sky (else we might have been able to pick out a Moon sized starless spot in the sky), and at this time, the entire Moon was dark. It would be interesting if someone could take a picture at a dark sky site showing a black Moon (round area without stars) at the height of this upcoming eclipse.

    1. Bob KingBob King Post author

      Hi Robert,
      Those really dark eclipses are unusual. I’ve never seen one but came close (bad weather). There’s always uncertainty about how dark or bright a particular eclipse might be. No telling exactly what this one will reveal, but we’ll know soon enough!

      1. Tom-Reiland

        I remember the one that Robert mentioned. We held a public Star Party at Wagman Observatory for that Eclipse and all of us were amazed at how dark that eclipse was compared to others that we observed. It was almost unobservable during mid-eclipse.
        One question about Mars, since it will be near the moon for a couple of nights. Do you know of any web pages, or is Sky & Telescope going to post something, for observing the Moons of Mars during this approach like they do with Saturn, Uranus and Neptune? I and others in the AAAP want to try to observe them once the Moon has moved away from Mars. I remember being able to see Phobos and Deimos in 2003 through my 16″ Dob and the 11″ Brashear Refractor.

  2. misha17

    The extremely long June 2123 total lunar eclipse belongs to Saros 132, the same series that gave us the lunar eclipse of April 4, 2015, which was either a briefly total eclipse (5-10 minutes of totality) or just a very deep partial eclipse
    (see comments here: https://www.skyandtelescope.com/astronomy-news/observing-news/preview-of-april-4ths-total-lunar-eclipse-033020152/ ).

    Fortunately our descendants won’t have to argue about whether 2123 eclipse is total or not!

      1. Milton LachmanMilton Lachman

        …and so you shouldn’t as the earth’s atmosphere doesn’t refract any light towards the centre of the umbra (as stated in the caption above to Anatomy of a Lunar Eclipse). The mechanism is scattering, which can be compounded when the moon is observed on the horizon – where every lunar eclipse may appear to be a blood moon. So why not use the term “dark moons” for central lunar eclipses, esp. ones where the centrepoint of the umbra gets covered by the moon?

        1. Bob KingBob King Post author

          Milton,

          You’re right, scattering removes the shorter wavelengths of light, allowing only the longer ones to make it to the Moon, but my understanding is that atmospheric refraction is a key factor in directing that reddened sunlight into Earth’s umbra and hence to the moon. “Dark moons” might sound like a good idea for central eclipses, but the term could confuse especially if a particular central eclipse is a relatively bright one. Every total eclipse results in a “blood moon” as it were, so I think “central eclipse” while dull-sounding, is at least accurate. Maybe you could jazz it up by calling it a “bullseye eclipse” 🙂

          1. Milton LachmanMilton Lachman

            If refraction were a key factor, then Snell’s law would allow us to see other colors of the rainbow in pastel hues (when not on the horizon). So conventional usage is wrong here just as it is for radio signals being “reflected” or “refracted” by the ionosphere where neither the law of equal angles nor Snell’s law are applicable (respectively), because (Compton) scattering is the key mechanism. “Bullseye Eclipses” gets my vote, as then one can leave “Dark Moons” for those occuring near perigee.

  3. Fabrice MoratFabrice Morat

    Hello Bob,

    From Canarian islands, it was a spectacle since mid-eclipse only with a low moon in nautical twilight. I’ve chosen an altitude site (La Palma Roque observatory, 2235m) along the road. Tenerife island was just in front of me. In these conditions, i’ve noted this eclipse between 1 and 2 on Danjon’s scale but nearer 2 because there was a left outer edge a little bright. The phenomena was better in 15×50 binoculars and even better in 25×141 Miyauchi. (contrast and copper colour were increased). Strangely, the general aspect was like your Stellarium simulation from Europe ! And it was variable in colour during the totality. At 45x, details in lunar maria were easy. Just before the end of the totality, the night was then deeper and milky way was the new spectacle. (SQMz 21.2). I had forgotten we could practice serious deep sky on this occasion !
    Fabrice M.

    1. Bob KingBob King Post author

      Great report, Fabrice, Thank you. I wondered how dark this eclipse would be. We got a full moon here in Duluth, Minn. and in honor of the Mars opposition we did some sidewalk astronomy. A few people wondered why the Moon wasn’t in eclipse, so I had to explain that sometimes we need to travel.

      1. Bob KingBob King Post author

        Thank you, Michel for your observation. I will send this information (along with Fabrice’s data) to Dr. Richard Keen for analysis.

  4. Joe P.

    Has anyone used Danjon’s scale — or, more ‘fruitfully,’ developed another — to describe the Full Moon’s color (especially rising or setting) throughtout the year?

    In June and (near-Full) in July, I noticed it rising in the twilight bow: pink strawberry & cream (especially last month — the traditional ‘Strawberry Moon’) to slight yellow to yellow-then-orange-peach. (Is the Moon ever pink outside high summer?)

    1. Bob KingBob King Post author

      Hi Joe,

      Thanks for your delicious description — it made me hungry! The Danjon scale is reserved for the eclipsed Moon. There’s no scale like it for a rising or setting Moon, the color of which continually changes in a matter of minutes. Like you, most of try our best to describe its many colors. As for the pink color of the Moon, yes, I can vouch it’s pink outside of summer

      1. Joe P.

        Glad to hear of lunar ice cream out of season.
        Is strawberry & cream served only at twilight risings?
        If so — is the full scoop (pink Full Moon) available only in summer?

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