Watch the lunar eclipse Saturday

By Phil Plait | December 9, 2011 10:00 am

Tomorrow (Saturday December 10) the Moon will pass into the Earth’s shadow, causing it to plunge into ruddy darkness, an event called a total lunar eclipse. These happen roughly twice a year somewhere on Earth, but this is the last one visible in North America for more than two years, so even though it’s in the morning it might be worth a look for you.

You can get all the info you need on watching the eclipse from my pal Alan Boyle over at the Cosmic Log, including timing, locations, and where to watch live online, too. NASA has a page with more detailed information as well. This one favors US folks farther west; the Moon will have set when the eclipse really starts for East Coast folks.

But the fun begins when the Moon starts to enter the deepest part of the Earth’s shadow at 12:45 UT (04:45 Pacific US time), and the last bit passes into shadow at 14:06 UT (06:06 Pacific). Deepest eclipse is about 25 minutes after that. Interestingly, for people in the western US, that’s around the same time as sunrise. For me, the Sun rises at 07:12 (Mountain time) Saturday, and the Moon sets at 07:14 — when it’s still partially eclipsed! Unfortunately, the mountains to the west will block my view of the setting Moon.

But for those of you with a clear horizon to the east and west, you may get an extraordinary opportunity to very briefly see the Sun and eclipsed Moon at the same time! Normally this isn’t possible; by definition the Moon and Sun have to be directly opposite each in the sky to get an eclipse at all.

But due to a quirk of geometry and atmospheric physics, it is possible. The Earth’s air acts like a lens, bending the light from objects near the horizon. Because of this effect — I give a full explanation here — you can actually see the Moon for a minute or two after it has physically set; its light is bent "around the corner", so to speak, so both it and the Sun will be over the horizon for a short amount of time. You can face west to see the setting eclipsed Moon, then turn around and see the rising Sun in the East!

Pretty cool. To see if you get a chance to experience this, check the time the Moon sets for you, the time the Sun rises, and compare them with the eclipse times from the NASA site (don’t forget to correct for time zone differences; Pacific time is UT – 8 hours).

NASA put up a nice video on YouTube describing all this. However, they make one mistake in it near and dear to me. Can you guess what it is?

Yup. They talk about the Moon Illusion — the Moon looking bigger on the horizon than overhead, saying,

Not only will the Moon be beautifully red, it will also be inflated by the Moon Illusion. For reasons not fully understood by astronomers or psychologists, low-hanging Moons look unnaturally large when they beam through trees, buildings, and other foreground objects. In fact, a low Moon is no wider than any other Moon — cameras prove it — but the human brain insists otherwise. To observers in the western United States the eclipse will appear super-sized.

ARRRGGG! That’s not correct. First, we do have a pretty good understanding of it! I have a detailed explanation of what causes the Moon Illusion, and it’s a combination of two well-known illusions: one of which is how we perceive the size of an object depending on its distance, and the other which makes us think the Moon is farther away on the horizon than when it’s overhead. Second, while the foreground object explanation is a very common one, at best it’s incomplete, and I think it’s not really relevant — the illusion still occurs when you have a flat horizon with no foreground objects (I’ve seen it in Kansas and Oklahoma while standing on farmland with nothing between me and the Moon but our own thin skin of air).

If you prefer explanations in cartoon form, then try this one at Sci-ence. I promise not to pop out of the bushes at you.

Anyway, when you put all this together, due to an atmospheric trick you have a chance to see the Sun and eclipsed Moon at the same time, and due to a brain trick they may both look huge as they squat on the horizon. If you’re in one of the locations where this is possible, go take a look! And if you get good pictures, link to them in the comments below, send a link to me via email (no attachments, please), and/or send them to Universe Today, which is always looking for good astrophotos.

Image credit: Anthony Ayiomamitis, who has a fantastic collection of eclipse pictures he’s taken over the years.

Related posts:

Why does the Moon look so huge on the horizon?
Didja see the eclipse?
My new favorite lunar eclipse image
In the shadow of the Earth
Incredible lunar eclipse floats near the Lagoon
Time lapsed: the Moon plunges into shadow
STUNNING lunar eclipse photo

CATEGORIZED UNDER: Astronomy, Cool stuff, NASA

Comments (49)

Links to this Post

  1. Friday Links | December 9, 2011
  2. Lunar Eclipse of the Day - TDW Geeks | December 9, 2011
  3. Lunar Eclipse and Sunrise (With Photos) | K-Squared Ramblings | December 10, 2011
  4. Saturday’s Lunar Eclipse « lequi100 | December 12, 2011
  1. Cathy W

    In my location, moonset is at 7:52 AM and sunrise is at 7:53 AM, and if I’m doing the calculations right the partial phase of the eclipse will have just started at 7:45 ET. I might actually get to see it (and maybe even the simultaneous sun-and-moon thing Phil was talking about…)

    …except that I checked the other relevant website: NOAA’s hourly weather forecast. They’re predicting 70% sky cover at around that time. My own forecast: even though I tend to be up at that time, even on a Saturday, I’m not seeing diddly squat.

  2. Grizzly

    Sunrise at 8:27, moonset 10 minutes later! Woohoo.

  3. JMW

    It would be cool if someone got a shot using a fish-eye lens of both the rising sun and setting, eclipsed moon…

  4. I loved the QI bit on the sunsets. I knew the effect was there, but I didn’t realize how much it was. Will have to tell folks about this.

  5. flip

    How annoying. I am perfectly situated to watch it, and yet, it’s cloudy now and the forecast throughout the day/night is also cloudy with possible rain.

    Darn it! I’ve never seen any kind of eclipse, and I was kind of hoping this would be my first….

  6. Kudos to Phil for battling mis-conceptions behind the “Moon illusion” once again… been waging a similar one surrounding the cause of a “selenelion” on our site: …refraction isn’t the sole cause of this unique eclipse phenomenon!

  7. Infinite123Lifer

    Nearby mountaintop




    Warning to the little rascals to be up 2 hours early


    Clear skies in WA

    DOH! Fingers crossed

  8. EricJuve

    I am lucky for once, If the weather holds. When I was on my way to work this morning the view of the moon was striking. About 10 degrees above the ocean as I crossed the Yaquina Bay Bridge at 6:30am in Newport, Oregon.

  9. I think we still might miss the possibility that objects that are bright (like the moon in the sky) impact our pupils making the object seem smaller while on the horizon the moon is much darker and it’s easier to look at stereoscopically. I’m not sure if that’s figured into our thinking about the Moon Illusion at all.

  10. Trebuchet

    I’m in Western Washington. What is this “sun” of which you speak?

    To be serious, it’s actually been clear all day. Maybe it’ll manage another 14 hours. We’re where we have a great view to the west, and normally get up at 6:30 anyhow. Sounds great!

  11. Talos42

    Is this article about an eclipse visible in Japan also correct? These kind of events can be global. Don’t forget about us expats just because you live in the states!

  12. VinceRN

    I’ll be at work and therefore likely awake, so I just have to hope for clear skies. Of course this is Seattle, so even with an unobstructed view to the west my odds are about the same as Phil’s.

  13. Infinite123Lifer

    Last night was just like tonight for all instinctual purposes, sky wise, maybe a bit less chilly. It always seems like an especially special and rather odd time to be alive when I have the chance to witness such wonders. Looking forward to a short hike & a cup of coco & hoping to catch the “double feature” of sunrise/Earth shadow.

    About the paragraph Phil mentioned, maybe I shouldn’t mention it but it is kind of. . . weird. For starters I think that’s the first time I have saw or heard the words astronomers and psychologists in the same sentence, nor the same paragraph, let alone seperated by an or! My psychologist will get a kick out of that & I feel as if there is a joke on the horizon! Aha

    Secondly, if the Moon does not change in size because “cameras prove it” when it crosses the sky how can this be? I would think at most points the Moon is either closer or farther away than it was the day before or even the second before, to assume otherwise would mean that the Moons orbit is basically circular rather than an ecclipse.

  14. Infinite123Lifer

    Which I think it basically is more circular than elliptical, but the “cameras prove it” line led me to think that the Moon never changed its distance from Earth I guess. If it moved only a fraction I guess that would not show up visually but how close to a “perfect circular orbit” does the Moon hav?

  15. Beer Case

    Here in Europe (Norway) we do not need to get up early. We’re going to see this in the afternoon! :) (The eclipse begins at around 3:30PM, CET)

    The weatherforecast is not good, though.

  16. @9. Infinite123Lifer :

    Clear skies in WA

    Er, you mean Western Australia? I thought you were American? ūüėČ

    Clear skies to all and to all a good lunar eclipse! :-)

    (Hoping to see this lunar eclipse myself, been very overcast here in Adelaide, South Australia, alas. Might have a break in the clouds perhaps – will certainly be out there checking for it around midnight here.)

  17. Naomi

    Well, the time isn’t too bad – around 1:30 AM for the greatest totality here in Sydney. Now, let’s hope the clouds play nice…

  18. Infinite123Lifer

    Maybe I was being a bit subjective but I always did like a play on words and sure why not MTU! Clear skies in Washington State and Western Australia mate!

    Happy natural wonder hunting. May the clouds resist their duty just long enough.


  19. flip

    Well, I was right… 9.30pm local time and it’s raining. Boo on the weather! :(

  20. Talos42

    Don’t feel bad flip. It’s also raining here in Japan. :(

    Think I’ll do now what I planned to do after the eclipse… get a drink at one of the local bars.

  21. Chris

    Hey Phil. You appear in the latest SMBC yet again. Apparently you are the reason we get eaten!

  22. flip

    #22 Talos42

    Unfortunately, I’m impatient and don’t want to wait til the next one ūüėČ

    Fortunately, I’m currently watching via SLOOH. Not quite the same, but it comes with commentary at least, and two of the telescope feeds are from my own country too.

  23. flip

    Spoke too soon. Now my internet connection is cutting in and out…

  24. Grizzly

    Clear skies despite some haze and Chinooky clouds earlier in the evening. It looks gorgeous! I’m out with my camera…

  25. Wow. Perfect, clear skies here north of Seattle. I got to watch the whole thing from the first nibble until totality, rare occurrence here. The sky gods smiled on us here for once. Not even fog.

    Beautiful, well worth freezing my @## off.

  26. Beer Case

    95% cloudcover in southwestern Norway. :(

  27. Trebuchet

    @me, #12, and VinceRN, #27: No clear skies here, northwest of Seattle. Bummer.

    As #23 notes, Phil makes yet another appearance in SMBC today. Be sure to hover over the votey button. Or maybe not, I’m going to have a hard time erasing the image from my mind!

  28. josie

    bleh. The Moon disappeared before it got to the horizon here in San Diego. Stupid hazy marine layer.

  29. Grand Lunar

    Saw the beginning of it this morning here in Phoenix (probably when 1/4 of the moon was in shadow) about quarter after 6am.

    My aunt and uncle joined me later when 2/3 was covered. Then my uncle and I watched the last sliver of it as the moon set. It was still above a tree when totality occurred.

    This was the first lunar eclipse I recall seeing at sunrise.

    Still haven’t seen a solar eclipse…..

  30. Ross Cunniff

    Saw the beginning as well. In Fort Collins we could not see totality because the Moon went behind the mountains well before moonset. My best photo is blogged here:

  31. Raymond Lang

    When I was living in Fairbanks, Alaska, we had a full moon that occurred around the Winter Solstice. Because of how high up Fairbanks is (in a latitude sense), we had a most unusual situation, where the moon rose at 11:20am on the 20th… and did not set until 1:31pm on the 24th of December in 1988. So we were able to see both the sun and the moon doing a celestial dance across the skies… the moon going high up while the sun stayed close to the horizon.

    [If you want to see the information, here’s the link: ]

  32. Clear skies here in Tucson. Lost the view in the brightening twilight right when totality set in. Blog and pics at

  33. Time-Lapse from Phil’s hometown in the Republic of Boulder –

  34. alek (37): Very nice! And I know just where you shot that; I bike there all the time. :)

  35. D’oh! I slept through it :(

  36. I stayed awake for it for the first time in my life and even have proof!
    Unfortunately my battery died like 1 minute later so I didn’t capture totality.

  37. David

    I have a question about the speed of light. Is this the right forum? 186000 miles per second, right? what if the miles are moving?

    Earth-surface miles are not static relative to other celestial objects. The implication is that the known physical laws may be relative to earth gravity but not other graveties. Is this a correct assumption?

  38. @ 41. David:

    The speed of light is the same for all observers. This implies that time runs at different rates for different people, length can shorten, and mass can increase. Space, time, length, and mass are not constants, but the speed of light is a constant.

  39. @21. Infinite123Lifer : December 10th, 2011 at 2:12 am

    Maybe I was being a bit subjective but I always did like a play on words and sure why not MTU! Clear skies in Washington State and Western Australia mate! Happy natural wonder hunting. May the clouds resist their duty just long enough.

    Cheers! :-)

    Don’t know how the skies were over Westralia. Alas, I needed the skies to be clear over the Adelaide hills – & they weren’t. :-(

    I got the odd glimpse of the eclipse of this lunar eclipse but only the odd glimpse for a few seconds through slight holes in the fast-moving clouds. Sigh.

    @41. David : December 10th, 2011 at 5:43 pm

    I have a question about the speed of light. Is this the right forum?

    Well, it is slightly off topic for this particular thread but that’s okay, I don’t mind & doubt anyone else would. I’d would also recommend asking that question on the BAUT (Bad Astronomy Universe Today) forum as an alternative forum for that as that’s pretty good for such questions but I’ll see what I can do for ya here as well.

    186000 miles per second, right? what if the miles are moving?

    Well, a mile is an unit of distance that should remain constant I’d say -can’t why it would chaneg unless you switch from miles to nautical miles or suchlike as your arbitrary measuring unit – although as an Aussie I’m, more used to the metric kilometres instead! ūüėČ

    Wikipedia, that usual & only slightly unreliable fount of all wisdom, has this linked to my name here :

    The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time.[1] In imperial units this speed is approximately 186,282 miles per second.

    I’ll stress the “in a vacuum” bit there as light will travel at different speeds through other mediums, eg. solid matter, liquid and plasmas – it apparently may take millions of years for a photon (particle – ray) of light to escape the solar core!

    Hope that helps.

  40. Infinite123Lifer

    Humble sigh.

    Spent all morning seeing shapes in horrendously dark and light grey enveloping tall walllike clouds both to the west and to the east. Not a natures hint was allowed save 5 fleeting minutes of glimpses at the very start after which the coming of the seemingly invisible wall of cloud shaped like a donut over our valley took its confining form. Quite perfectly concealing. ūüėČ

    Can’t win em all

  41. Hi Bad Astronomy fans, I’m working on a timelapse of the eclipse as seen from Maple Ridge BC, Canada. I’ve got about 1100 shots taken at 5 second intervals from just before first contact of the Umbra until I lost the moon in clouds and behind my neighbour’s roof 15 minutes into totality.

    It’s not ready yet, but in the mean time, the first 4 images in this Flickr set show the eclipse close-up, and my setup:

  42. Unfortunately, I was unable to see the lunar eclipse in Orange, CA, not because it did not occur, but because I was asleep. :( This is quite upsetting because I am sure it was a sight to see. Not being an astronomer and not fully understanding the laws of astrophysics would have probably made the experience all the more bewildering and amazing.

    After reading the explanation of the illusion of a bigger moon on the horizon than that higher in the sky, I was a little confused. So, being the visual learner I am, I took a look at the comic illustrating the illusion; it now makes much more sense. It is quite amazing how perspective can cause such a great difference in the way we visually and cognitively interpret something, even though we KNOW the illusion to be false. In order to get an even better understanding of the Ponzo Illusion, I plan to also read “Why does the Moon look so huge on the horizon?”.

  43. nancyem

    It was very cool! I’m in north San Diego county, clearer skies here. Drove up the coast from Oceanside (too many lights at the beach) to Ave de las Pulgas (off I-5 in Camp Pendleton). Perfect darkness, good spot to watch! Right after totality the sun started to rise, and the moon was lost in the growing light.

  44. Hedgie

    I thought I’d share a few shots I took. All of these were taken freehand (my sister-in-law has my tripod) as I crouched and leant against my letterbox to stop myself falling over.


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