Ring around the Moon

By Phil Plait | November 7, 2011 7:00 am

Last night, my in-laws came over for dinner. As I was helping them take leftovers out to their car around 9:00, I do what I always do when I walk outside at night: I looked up.

And man oh man, am I glad I did. Because this is what I saw:

Wow! [Click to refractenate.]

As soon as I saw this, I ran back inside, grabbed my camera, and took this shot. The bright blob in the middle is the Moon — it was just past half full. The "star" to the left is Jupiter, now shining brightly in the east shortly after sunset (the blue and green patches are reflections of the bright Moon inside the camera). You can also see a couple of stars in the constellation Aries just above Jupiter. But dominating the sky was the bright ring around the Moon, called the 22° halo.

Halos like this are caused by ice crystals suspended in the air. The crystals are hexagonal, and light entering one face of the hexagon gets slightly bent, and then bent again as it comes out. The total angle of bending is (at least) 22°, and this is what forms the ring 22° in radius.

Different colors are bent by different amounts; red is bent slightly less than blue, so the inner edge of the halo is red (look at the picture carefully and you’ll see that’s true). The inside of the halo is slightly darker than the sky around it, because no light is bent less than 22°. Light coming to you from the Moon inside that 22° limit gets bent away from you, so you don’t see it. Light outside that limit gets bent toward you, making the bright ring. The halo is actually pretty broad, but fades rapidly outside 23 or so degrees from the Moon, so it looks like a halo. In reality it’s more like a disk with a hole in it.

I love how Jupiter is sitting just outside the ring; in a couple of days the Moon will swing past the giant planet in our sky, missing it by just about 4° (roughly 8 times the size of the Moon’s disk itself). That’ll be a lovely sight.

The picture above was a ten second exposure at f/2.8 and an ISO of 400. Those are standard settings, so it can be pretty easy to take dramatic pictures of the night sky… when the subject is this beautiful.

I’ve seen halos many, many times — though this one was really spectacular. Still, the reason I’ve seen so many is quite simple: I look up. Seriously, that’s all it takes. What glories of nature are you missing by not looking around you?

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Polarized rainbow, what does this mean???

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: halo, Jupiter, Moon

Comments (50)

Links to this Post

  1. Moon Rings | Travel America | January 9, 2012
  2. Barefoot and Naked | Tidbits of My Mind | January 21, 2012
  1. Chris

    For an added treat Phil has been featured in today’s Saturday Morning Breakfast Cereal.

  2. Daniel J. Andrews

    till, the reason I’ve seen so many is quite simple: I look up. Seriously, that’s all it takes. What glories of nature are you missing by not looking around you?

    A friend, who lives in the city, had gone to a family camp in northern Ontario where there were few lights. He later told me that he had been there for three days before he remembered that I had told him he should always look up at the sky whenever he’s outside as even in the city there are things he can see. Once he remembered and looked up, he was entranced…he says the stars were so beautiful and bright. He went on about how he could see little fuzzy spots (nebulas and clusters), satellites, the occasional meteor, etc. He was slightly embarrassed that it had taken him three days to remember to look up at the sky at night, but was quite excited about what he was seeing.

  3. Just last night I got a chance to look up and see Jupiter for myself. This after looking up sometime after noon and seeing a beautifully lit moon in the day time sky. I’m sad I missed this halo, but I definitely love seeing them.

  4. Stephen Crowley

    Sorry to be pedantic but the pixels that just popped up on my monitor is a representation of what you saw, not what you saw. :) Beautiful, though.

  5. Ohio Mike

    Cool! When I see the ‘ring around the moon’ I always close one eye and obscure the moon with my thumb…the colors really come out then!

  6. Trebuchet

    Beautiful. However, Phil, we’re big boys and girls here. You don’t have to say “just past half full”. “Waxing Gibbous” probably works for most of us and sounds cool to boot.

    And putting weapons on telescopes? Only if they’re pointed a killer asteroids!

  7. JS

    Thank you so much for writing about this –I saw this last night too! I was entranced and thought it was my aging eyes playing tricks on me. Thank you for explaining this. I am a proud space geek who always takes a minute to look up at he sky for inspiration. I wish the policy makers in Washington DC would do the same—then they would not have any hesitation funding NASA space programs the way they should be.

  8. Don K

    Hey Phil,

    I live about 14 miles West of Boulder, and I only saw the bottom of the halo, as the high cirrus didn’t reach far enough. However, my photo was not nearly as good as yours!

  9. Phil, this is 2 days in a row that I can post a like to a picture that is similar to one in your posts: http://bit.ly/sfhalo is a picture I took in May 1995 when I visited San Francisco for the first time in my life. There, with the sun high in the sky, I watched up primarily to see the upper parts of the impressive buildings. I stumbled upon the 22 degree ring around the sun. Deeply impressive indeed. I spent quite some time watching the sky (and getting weird looks from innocent bystanders) instead of enjoying the beauty of the city itself!

  10. Robin Byron

    “…(the blue and green patches are reflections of the bright Moon inside the camera).”

    But wouldn’t it be cool of they were Moon moons or nearby planets?
    Even better would be to see Andromeda near enough to cover, say, three quarters of the night/day sky. Hmm, I can easily imagine that but have any artists depicted that image?
    The astounding grandeur our cosmos and we have so little time here to appreciate it. I want more time, dammit.
    Guess I’ve had enough coffee for today.

  11. DrBB

    Been watching the ultra-slow motion Jupiter-Moon dance these last couple of weeks with delight. It’s been great to have an astronomical ballet I can make out in the light polluted skies of Somerville MA. Nice to know what’s coming up. I’ll be keeping an eye out for that near-conjunction.

  12. Dedalus

    I know what you’re saying about “not looking up.” This year, I played a “teacher of SCIENCE!” at Netherworld Haunted House in Atlanta, and one of my bits was to point out stuff in the sky (so my scarier friends could sneak up). I was appalled at how many people flatly rejected my identification of Jupiter, and, even worse, I was appalled that MOST people identified the moon as “Last Quarter” even though it was shortly after sunset. On the other hand, I tried to be excited about the sky, and even got some folks to Google “Hanny’s Voorwerp.” There is hope!

  13. jason

    If I remember reading correctly won’t the moon pass in front of Jupiter in Dec?

  14. Jason Pomerantz

    Thanks for explaining this!

    I remember wondering about this in high school and asking my physics teacher what it was. He had no clue!

    I’ve noticed the halo around the moon many times since then, but this is the first time I’ve ever started to understand what I was seeing.

  15. Jon Shurtlee

    I’m a big boy and I would not had known what waxing gibbous meant.

  16. W Sanders

    When the moon isn’t around and it’s really dark, and similar ice crystals are in the air, you can see a ring around Jupiter. Jupiter-dogs!

  17. That_Guy

    “…(the blue and green patches are reflections of the bright Moon inside the camera).”

    So you claim. “They” got to you, didn’t they? You can’t hide the truth! We KNOW those were the advance scout ships for the asteroid!

  18. Joseph G

    @#1 Chris:For an added treat Phil has been featured in today’s Saturday Morning Breakfast Cereal.
    [URL baleeted, see original post]

    I think SMBC just built the successor to the JWST. All we need is a truly massive multi-mirror telescope, and for Phil to hint to the budget subcommittee that maybe, just maybe, if the need arose, the wizards at NASA could reprogram it to reflect a solar death ray onto a planetside target.
    It doesn’t need to be true, it just needs to sound nice. That’s typically enough for our Congress.

  19. Infinite123Lifer

    Cool. I saw the same thing last night in Washington. I watched the moon most of the night as it cruised over our house and with the slight cloud cover there were some pretty outstanding halo’s! I saw this huge bright star? right outside the halo as well. I thought it might be Vega but it didn’t seem quite right. I checked my Google Star Maps and surenuff! it was Jupiter.

    I should of known. I have been watching Jupiter cruise the skies behind the Moon for the past couple months or so. During this time I think it has been significantly brighter than even Vega. It is quite dominant in the sky.

    It is so cool to know that even though everybody is so far apart, we can still experience the dynamic of what is Life on Earth with similar sights. Even better when everyone agrees on what we are seeing :)

  20. Meskine

    When I was growing up, one nugget of sage country wisdom imparted by the tribal elders was that when you saw a halo around the Moon, precipitation was imminent. Whenever I see a halo, I ooh and aah for a few minutes and think to myslef, “Rain’s a-comin.” But in all those many years, I have never written myself a note to pay attention to whether it rained within the next day or two. You saw the halo last night and I see where NOAA is predicting 70% chance of snow for Boulder tonight, so I guess those old poops knew what they were talking about.

  21. Mike Sperry

    When I was a teenager, I was out late one night taking a walk. This was in a suburb of Los Angeles (a little town called El Segundo) so there was a LOT of light pollution. There was a bright moon, about the same phase as this one, with a ring around it.
    At one point, I looked up and a shooting star zipped right through the ring! Given the amount of light pollution in that area (not to mention the Moon washing out the darkness), I figure it had to be a bolide based on how bright it was.
    It was a one-in-a-billion chance that I glanced up at the exact right moment to see that.
    I was stunned by the beauty of the moment.

  22. Wzrd1

    I must be getting too old. I viewed the photo after reading the first paragraph and thought, “So, what’? It’s ice creating a halo illusion. Seen it thousands of times, a few times even more pronounced, with less clouds.”
    Then, I read the article.
    I considered the source.
    Then, began to sadly consider myself ancient and jaded, though I DO look up incessantly.

    But then, many, many, many others don’t understand the phenomena and can’t comprehend what Phil so easily explained.
    I see it and consider the refraction errors that those crystals will induce in any decent telescope image, from my bygone days of gazing through a telescope. My eyes aren’t that good any longer and I can’t afford a good imager for quite a while yet. :/
    First, the usual bills, taxes, get three years of overseas income taxes done, THEN hearing aids ($4000 right there), THEN one posterior lens capsule lasered through, THEN the other cataract removed.
    THEN, I might be able to see an image through a telescope a bit again. Just not as well as when I was younger, as I also have lattice degeneration. :/

  23. Infinite123Lifer

    Hang in there Wzrd1. You seem to be an expert at it! 😉

    I hope to have the privilege to grow so old.

    “None are so old as those who have outlived enthusiasm.” ~Henry David Thoreau

    I hope you can get that good imager! :)

  24. Infinite123Lifer


    I hope to have the opportunity to LIVE so long!

  25. Joe

    A weeks ago Phil had me running to a dictionary to look up the word “Embiggen” which he used beneath a photo in a caption: Click here to Embiggen. It is not a real word and is sometimes mistakenly used for “enlarge.” Well, he’s at it again. Below his above photo he says to “Click to refractenate.” I googled this one. It doesn’t exist anywhere, in any form, for any purpose. Damn, he’s good. The Professor Irwin Corey of astronomy.

  26. pavium

    What you say about looking up is true.

    I worked with a person a few years back who had reached middle age without realising that the Moon is sometimes up during the day.

    It all comes from not looking up…

  27. Wzrd1

    Joe, you’re obviously new here.
    Phil invents these words to keep interest and generate a chuckle. Just as I, the house dictionary and encyclopedia, in a house with 6 dictionaries and 3 encyclopedias, started using words like “gooder” when our eldest child started college.
    It got her attention. 😉
    Honestly, I’d rather he invent a word here and there than invent facts, like certain political candidates do on a regular basis!

    @Infinite123Lifer #23, yes, I’m quite proficient at surviving. The only annoying thing is, I just turned 50 last Saturday. There ARE two things I’ve learned in life:
    1: Interesting lives are typically marked by their brevity.
    2: I’ve managed to survive an interesting life, a bit worse for wear.
    It’s just extremely annoying, can’t see in the dark worth a dime any longer, can’t hear and enjoy my music any longer (hearing loss and tinnitus) and some joker keeps extending the distance I have to stretch to reach between up and down. 😉
    I also do an excellent impersonation of rice crispies in the morning, snap, crackle and pop. :/

  28. Kay

    I love this site and check it almost daily. Although I’m fascinated with the science Phill talks about, I’m not smart enough (or disciplined enough) to nail down all the specifics of the science, which is why I enjoy reading Bad Astronomy. Phill spoon feeds me what I need to know to appreciate how fascinating the universe truly is.

    But I couldn’t help but chuckle at the statement…”the bright blob in the middle is the Moon…” Come on..even I knew the bright blob was called the Moon! :)

  29. Jim

    Robin @10: Better than Andromeda, we have the Milky Way up close and personal and it’s really not that bright. Spectacular from a dark location, but I find it somehow disappointing when I think about how many stars there are in the Milky Way and how faint they appear to the naked eye.

  30. Meskine

    @Wzrd1: I feel your pain my brother. I’m 54, and rather than treat my body as a temple, I treated it more like an amuement park ride. When I roll out of bed in the morning, it takes a few minutes to get fully erect. Unfortunately, there are some parts that no longer seem to get fully erect. (I’m talking arthritc fingers here, you filthy minded perverts.)

  31. Wzrd1

    @Meskine, that’ll come soon enough for me. I already have Raynaud’s, which is quite firmly linked to rheumatoid arthritis, so, it’ll come. :/
    A for treating my body as a temple, never had the time to worship, I was on duty in unpleasant places. :)
    So, it’s a necessary and accepted sacrifice for surviving an exciting and eventful life that I cannot relate. But, there were many fine moments.
    I figured it was time to retire and try civilian life after I had lost as many men and buddies in total over my career as I had years of service (over 27), figured 28 might be me. Besides, old torn rotator cuffs made putting body armor on like the labors of Heracles.

  32. Goodest

    I’ve seen moon halos all the time. But I’ve only seen an asphault halo once.

  33. Musical Lottie

    Wow. I was lamenting to my mother last night that I hadn’t seen the stars for at least a week (but quite possibly longer) – it’s been 100% cloud cover, and the past few days we’ve had nothing but mist all day and all night. So while this photo makes me long even more to see beyond the clouds again, it’s also a lovely way to sort of see past the clouds by proxy :)

    And I’ve never heard of or [knowingly] seen a 22° halo; even if it’s the only thing I shall have learned today I shall be very happy indeed!

  34. jordan

    its cuz of chemtrails at night man

  35. steven tan

    last month 9/10/11 night in Malaysia I took 2 photo ring around the moon but it came out very strange there was a huge spaceship (one part of it) and a lots (maybe thousand) transparent aliens on board that spaceship (mother spaceship)not a small flying saucer NO JOKING go to my face book Steven Tan meng hui please Zoom the photo and analyse the moon and the spaceship or E-mail smhtan@hotmail.com I will sent some parts photo have been Zoom

  36. .

    hey! here’s another picture of the same thing in Israel at 10/11/11:

  37. that happens ever five years and i dont know how long they last for and what month it starts
    but my guess is that it will be in 5 years on october idk what day bc 5 years ago i think i saw it in december but im not sure its just a guess so it could be nov since this month i just seen it again 11th idk and it looks amazing but it hits that 22 angle ever 5 years idk know the months

  38. MaureenM

    I live in LA, and the night that the moon and Jupiter were closest I was out walking my dog and (of course) looked up at the moon. I gasped as I saw a gorgeous halo around the moon and Jupiter, and just as I gasped, a meteor shot through one side of the halo. It was so completely awesome. I sent a big thank you up to the skies that night, and yes, I am very glad I looked up!

  39. steven tan

    Go to search transparent UFO aliens on board huge space ship that photo I took on the night ring around the moon in Malaysia.

  40. Rawinia

    I saw a ring around the moon tonight. in past occasions when ive seen a ring around the moon it was raining the next morning without a doubt.ive seen about 4 or 5 in my lifetime and not one of them failed me…by the time i wake up…raining…i feel really guttered because i love looking at the night sky but i dont see much these days coz i live in the city compared to when i was little i always lived away from the city and i used to see everything in the night sky. i miss that

  41. Are there halos of different diameters? I’m pretty sure I’ve seen one about 10 degrees in radius, because I realized that would be the size of Jupiter if it took the Moon’s place. It’s fun to imagine Jupiter (or whatever is size-appropriate for the halo) actually being there.

  42. Kelly

    Saw this a couple nights here in good ol’ colorado…pretty beautiful.

  43. netty

    I lived in bush alaska for years before seeing the Northern lights and was teased mercilessly for ‘kicking rocks’. “looking up”–its good advice, whether to see stars or if one is in an action movie

  44. claire

    I live in south Florida and the moon has a halo “ring” around it toni9ht 8:50pm…..wow what a sight! In my 65 years of life I have never seen a halo around the moon. I tried to take a photo but it did not come out.

  45. Becky

    I’m 48 years old and I live in Kentucky. I have never seen the halo around the mo0n until 02-03-2012. It was right after my Sister passed away @ 7:30pm est. Some say it means 3 days of rain or snow. yes we had rain the next day. But call me crazy but me and all my family that was there when my sister passed away we think it was my sister letting us know she was in Heaven rejoicing with all of our family member that have done gone to meet our Lord and Savior. A lot of family,friends and our church Family saw this. But some friends that lives in the same town didn’t see this. it only lasted for a couple hours then it was gone.

  46. Jeffrey

    Man, I’ve should have done the same, I think last week or 2 weeks ago, I saw the same thing but it was on Venus, not the moon, all I had was my iPhone and the photo wasn’t great.

  47. Lori

    I live in northern IL and I saw part of a moon ring last night while looking at the blue moon this month. The moon was covered by a thin layer of clouds and the partial ring (semi circle) appeared on the lower half of the moon. On the night of 6/19/12, exactly a week after my father passed away, I was looking up at the evening sky and I asked my father if he could send me a sign, a shooting star (meteor) and seconds later I saw a HUGE shooting star/meteor. It flashed from left to right and it was so huge and bright, like a firecracker. It happened so fast before it disappeared behind the tall trees in my backyard. Truly amazing.

  48. Bruce Terris

    I been seeing this ring around the moon for the last two nights, and to night it was very clearto see.
    so of corse I had never seen this before and had to find out what this ring was all about. Thanks for sharing this so that poeple like me that have never seen this before know now what this great thing is all about. It is truely amazing.


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