A Sky-High Lunar Eclipse

UPDATE: Cloudy? Watch a webcast here, here, or here.


It's been almost three years since those of us in North America saw a total lunar eclipse.

Visibility of December's lunar eclipse
North and Central America see the entire eclipse from start to finish. Europe, Australia, and East Asia can only observe some of it due to the Moon setting or rising. Click on the image for a larger view.
Sky & Telescope illustration
Now the whole continent is in for another on Monday night and Tuesday morning, December 20-21. Earth's shadow will totally engulf the Moon from 2:41 to 3:53 a.m. Eastern Standard Time, or 11:41 p.m. to 12:53 a.m. Pacific Standard Time, as shown in the timetable below. The partial phases of the eclipse will last for a little more than an hour beforehand and afterward.

Unlike a solar eclipse, each stage of a lunar eclipse is visible to everyone on the Moon-facing side of Earth. Observers in Europe, West Africa, and South America will see part of the eclipse before it's interrupted by moonset and sunrise on the morning of the 21st. In East Asia, Australia, and New Zealand, the eclipse is already in progress at sunset and moonrise on 21st local date.

The Moon will be at the northernmost part of the ecliptic, north of Orion between the feet of Gemini and the horns of Taurus. An eclipsed Moon is always full, so if the eclipse happens in the middle of the night for your location the eclipsed Moon will be about as close as it can ever be to straight overhead.

Total Eclipse of the Moon, December 20–21, 2010
Eclipse eventESTCSTMSTPST
Penumbra first seen?12:55 am11:55 pm10:55 pm9:55 pm
Partial eclipse begins1:33 am12:33 am11:33 pm10:33 pm
Total eclipse begins2:41 am1:41 am12:41 am11:41 pm
Mid-eclipse3:17 am2:17 am1:17 am12:17 am
Total eclipse ends3:53 am2:53 am1:53 am12:53 am
Partial eclipse ends5:01 am4:01 am3:01 am2:01 am
Penumbra last seen?5:35 am4:35 am3:35 am2:35 am

A total lunar eclipse has five distinct stages. It begins when the Moon first enters the penumbra, or pale outer fringe, of Earth's shadow. But this event is unobservable; the shading in the outer part of the penumbra is extremely slight. Not until the Moon's leading edge is about halfway across the penumbra does the first slight dimming become detectable to the eye.

Times for December's lunar eclipse
Key events and times for December's total lunar eclipse. You should be able to detect penumbral shading on the lunar disk about a half hour before the partial eclipse begins and again for a half hour after the partial eclipse ends.
Sky & Telescope illustration
The second stage, partial eclipse, starts when the Moon's edge reaches the umbra, or Earth's inner shadow. Few sights in astronomy are more eerie and impressive than watching this black-red shadow creeping, minute by minute, across the bright lunar landscape. You'll soon notice that Earth's shadow has a curved edge — visible proof that the world we live on is round.

As more of the Moon slides into the umbra, look around the sky. You'll notice that a second, deeper night is falling around you — night within night. In fact, if you're far from city lights, hundreds of additional stars start appearing in what earlier was a bright, moonlight-washed sky. An hour or so into partial eclipse, only a final bright sliver of Moon remains outside the umbra — and the rest of it shows an eerie reddish glow.

The third stage, totality, begins when the last bit of Moon slips into the umbra. For this eclipse, totality lasts a generous 72 minutes.

Then, as the Moon continues moving eastward along its orbit, events unwind in reverse order. Totality ends when the Moon's leading edge reemerges into sunlight, returning once again to a partial eclipse (stage four). Then, after all of the Moon escapes the umbra, the dusky penumbral shading (stage five) gradually fades away, leaving the full Moon shining as brightly as if nothing had happened.

The start of totality
"This matches the view in my 15 × 50 Canon IS binoculars very nicely," writes Rick Fienberg. He shot this picture during the February 2008 lunar eclipse just as totality was beginning, using a Tele-Vue 85-mm refractor as the lens on a Canon 20Da camera; 1-second exposure at ISO 400.
S&T: Richard T. Fienberg
Red in the Darkness

The umbra is the part of Earth's shadow where the Sun is blocked from the Moon completely. So why does the Moon here glow deep orange or red, rather than being completely blacked out?

That red light you see on the Moon during a lunar eclipse comes from all the sunrises and sunsets that ring the Earth at the time. Our atmosphere scatters and refracts (bends) the sunlight that grazes the rim of our globe, sending it into Earth's shadow. If you were an astronaut on the Moon, the situation would be obvious. You would see the Sun covered up by a dark Earth that was ringed all around with a thin, brilliant band of sunset- and sunrise-colored light.

On rare occasions the eclipsed Moon does go black. Other times it appears as bright and coppery orange as a fresh penny. And sometimes it turns brown like chocolate, or as dark red as dried blood. Two factors affect an eclipse's color and brightness. The first is simply how deeply the Moon goes into the umbra. The center of the umbra is much darker than its edges. This time the Moon will pass fairly deep through the umbra, and at mid-eclipse the Moon's southern limb almost reaches the umbra's center. The other factor is the state of Earth's atmosphere along the sunrise-sunset line. If the air is very clear, the eclipse is bright. But if a major volcanic eruption has polluted the stratosphere with thin haze, the eclipse will be dark red, ashen gray, or blood-black.

In addition, blue light refracted by Earth's clear, ozone-rich upper atmosphere can also add to the scene, especially near the umbra's edge, creating a subtle mix of changing colors. Such variable shading can give the eclipsed Moon a very three-dimensional appearance.

The next eclipse of the Moon is a deep total one on June 15, 2011, but North America misses out completely. Skywatchers on the West Coast can catch part of the following one, on the morning of December 10, 2011, until it's interrupted by moonset and sunrise. The next total lunar eclipse for the whole continent doesn't come until April 14-15, 2014 — an unusually long wait. So hope for good weather this time.

Extra-credit projects

  • In a telescope, can you spot any faint stars close to the Moon during totality? Any star just to the Moon's east will soon be occulted (covered). Normally the full Moon is so bright that even in a telescope you can see only the brightest stars as they approach its edge. But during totality, even the smallest telescope may reveal faint stars coming right up to the colorful lunar disk and suddenly winking out as it covers them up.
  • Roger Sinnott continues to collect amateurs' telescopic timings of when the edge of the umbra crosses lunar craters, as part of a decades-long project tracking slight unpredictability in the umbra's diameter. For crater maps, instructions, and where to report your timings, click here.
  • John Westfall continues to collect timings of the four contacts, when the partial phase begins and ends before and after totality, made with the unaided eye. This information will help calibrate the historical timings made by mariners and others when this was one of the few ways to determine longitude at sea. For more information, click here.

20 thoughts on “A Sky-High Lunar Eclipse

  1. Marvin

    How often does a full moon occur on Winter Solstice?

    How often does a Lunar Eclipse occur on Winter Solstice?

    I would think that this is quite unique.

  2. Sam Beam

    @Marvin, good question. The moon is always full during an eclipse, right? According to NASA’s LE catalog, the last Total Eclipse on Dec 21 was in 93 AD – I wonder if Caesar saw it.

  3. David Fried

    This reminded me of the lunar eclipse of December 30, 1963, which was dark as any I have seen. I find that on December 30 the Sun is only 14 minutes, or half a lunar diameter, north of its declination at the Solstice, and daylight at the latitude of Boston (if that’s what you call it) is only 3 minutes longer.

    Obviously what’s cool about a winter eclipse is the moon riding high in the heavens. The diameter of the Earth’s shadow at the distance of the Moon is about 8800km. The diameter of the Moon is 3500 km. This makes the shadow about 75 min. of arc in breadth. So the declination of the Moon at a solstitial eclipse can vary a lot more than 14 minutes.

    My conclusion? The eclipse on December 30, 1963 was, considered as a solstitial eclipse, good enough for government work. So if the weather is bad on Monday, or if it’s just too cold to go out (and the combined odds exceed 100 percent), I’ve already seen my solstice eclipse, not to mention my Red Sox eclipse. . . thank you for listening. I feel better already.

  4. atook

    Sam!
    Domitian was Emperor in 93 AD.
    Not being a dick. I had to look it up!
    Wishing you clear skys!
    XOXOXOXO
    Atook

  5. Michael J. Hutchinson

    I remembered that I watched the total lunar eclipse of December 30, 1982, using my old 6-inch Newtonian telescope, and noticed the umbra was totally invisible, during partial phases, that surprised. It was ashes over the skies. It was very cold–just 4 degrees. I saw total lunar eclipse on the night of November 28-29, 1993, it was mostly cloudy, but it allowed me to see total lunar eclipse. Will it be repeat of 1993 eclipse? Well, I will find out, if it will be too cloudy, go to http://www.ccssc.org/webcast.html!

  6. Michael J. Hutchinson

    I remembered that I watched the total lunar eclipse of December 30, 1982, using my old 6-inch Newtonian telescope, and noticed the umbra was totally invisible, during partial phases, that surprised. It was ashes over the skies. It was very cold–just 4 degrees. I saw total lunar eclipse on the night of November 28-29, 1993, it was mostly cloudy, but it allowed me to see total lunar eclipse. Will it be repeat of 1993 eclipse? Well, I will find out, if it will be too cloudy, go to http://www.ccssc.org/webcast.html!

  7. Mike Coren

    David, Michael, thanks for sharing your stories. Lunar eclipses are infrequent enough that they become sort of an amateur astronomer’s version of the “I remember where I was when I heard Kennedy was assassinated.” This one coming up on December 21 is the Saros equivalent of the one in December, 1992. I remember that one vividly. I was living in Edinburgh, Scotland, at the time. I gathered with the Edinburgh Astronomical Society to watch it from the historic City Observatory on Calton Hill. I remember it being a very dark eclipse.

  8. Maui Star Gazer

    A passing cold front is threatening to eclipse Hawaii’s view of the eclipse! Maui Astronmy Club and Haleakala Amateur Astronomers are both planning to view from the summit of Haleakala, a 10,000 foot volcano. A view of this link http://www.prh.noaa.gov/hnl/satellite/Hawaii_IR_loop.gif will show that the back side of the cold front may pass by in time to open a window into the eclipse event. We’re all waiting for the cloud abatement miracle. Personally, I am hoping too that Santa delivered my new REI snow pants cuz even though it’s Hawaii, the temperature will likely drop into the 20s. What we call freaking cold in these parts!
    First lunar eclipse on the winter solstice in over 600 years…gotta have hope!

  9. David Fried

    Well, it’s 10:30 pm EST in Boston, and we’re snowed out by the first storm of the season. I am a prophet, if a prophet is ever needed to predict bad weather here. It’s particularly too bad, because I actually have to catch a plane at 5:00 am, so would have to be up anyway.

    Mike Hutchinson’s eclipse of 12/30/82 is, I assume, the saros equivalent of the one I saw on 12/30/1963, exactly 19 years before.

  10. A. Grant

    They say that there are billions of people going to witness the lunar eclipse tonight, but I have discovered that this is a farce on most of the east coast due to a long band of snow clouds. I have stood outside and watched these clouds move up down and from side to side, which is really annoying to say the least. What should become a clearing in the clouds moves to cover the moon! Is this happening anywhere else or is it that nobody in my neck of the woods was meant to see the eclipse. This day in age there are several government experiments going on; could this be one of them? I find this to be very disappointing as I will probably not get witness another in quite a long time! Especially like this one!!! Also the moon seems to have this fake luminecant color to it, is this normal? It looks fake!?! Any opinions would be appreciated! Thanks

  11. Ree

    No snow, but bands of slight clouds – enough that you can’t see anything. Nothing like being outside at 18°and not being able to see anything !!!!

  12. Bronx amateur

    spectacular color changes to totality “orangey” with some wispy cloud cover for awhile with wind gusts then clearing while bright sliver across top became a “headband” of brightness.

  13. David Gan

    I have seen a number of total lunar eclipses, but this one is different and I wonder if someone else has seen what I have seen. During the last phase, as the Earth’s shadow was leaving the moon, I noticed a bright spot in the shadow, star like in appearance. It was about 0100 hours PST, then as the shadow left this area, it revealed a larger white round spot with a ray pointing to the right. My guess is that the star light spot was the reflection from the top of a peak? Ic tould be a very bright crater with a ray. I like to hear is someone else noticed this sighting.

  14. Bronx amateur

    After totality, across shadow edge, observed deepened dark contrasts of lunar surface “map”. Brigthening moonlight as our disk of shadow slips down and clouds created ring-around-the-moon, a glowing frame for this winter-night eclipse. Patience, small binoculars, and the moon.
    Eastchester Bay, Bronx, NYC

  15. Jean LoupdonYan

    There is a mistake with dates of last Solstice Eclipse: iu was on the 21rt of December, 1638. (NASA data, US Naval Observatory data)

    That year, Galileo publoshed “Discourses and Mathematical Demonstrations Relating to Two New Sciences (1638; in Italian: Discorsi e Dimostrazioni Matematiche, intorno a due nuove scienze)”

    Merry Christnas, FELiZ NAViDAD from México! (the dlearest skyes during all the Eclipse, here North of Cuernavaca)

  16. David C. Gan

    I have seen a snumber of total lunar eclipses, but this one is different. It was during the last phase when the shadow was starting to leave, I saw s star-like bright spot near the edge of the shadow. Hey, somebody left the lights on on the Moon. Then the shadosw left exposing a very white and bright crater with a short ray pointing to the right. So what I might have seen was a peak in the crater ot the crater itself was somehow reflecting light. Has anyone seen this event? It was about 0100 hours PST Berkeley California when the clouds cleared temporarily. I saw it on my 6 inch Newtonian telescope 60X.

  17. Bronx amateur

    Sequence inspires search for more info and grateful to photographers’ time lapse and sequence photos posted on skypub. Thank you so I can share what I viewed first-hand.

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