Moon Doggies

By Phil Plait | September 17, 2008 3:00 pm

Reading NoisyAstronomer’s tweets, I saw she linked to a great picture of a halo around the Moon (a small version is on the left, click to enlargenate) taken by Rachael Beaton, a grad student at UVa.

Halos form when ice crystals in the air refract the light from a bright source, bending it back toward you. They’re common around the Sun, and a bit less common around the Moon because the Moon is fainter (though the sky is darker at night, giving you better contrast). But the little rainbow flare you can see off to the side is much rarer in Moon bows. Called parhelia (or sundogs), they have a similar origin as the bow, but are due to flat, hexagonal-shaped ice crystals. I don’t think I’ve ever seen a Moon dog!

And that little blue gizmo off to the side is a new one on me as well! Cool.

Also cool, in that picture, is that you can see the tube of the old 6″ telescope at UVa, built over 100 years ago and still a fine piece of work. Back in 1994 I used that ‘scope to observe the scars left on the top of Jupiter’s atmosphere by the impact of Shoemaker-Levy 9, a comet that broke into pieces and repeatedly slammed Jupiter. I could see them as small but perfectly formed black spots on the planet. It was awe-inspiring, to see impact remnants larger than Earth, knowing that impacts like that on our own planet would have wiped us out as a species.

… hmmm… it’s cool, where your mind wanders, and where a single picture can take you.


Comments (35)

  1. Err. Isn’t the ‘little blue gizmo’ lens flare? Greeny-blue is a common colour because it’s often reflected by multi-coated surfaces inside modern camera lenses.

  2. Click on my name and the link will lead you to a fantastic example of a Moon-dog.

  3. Trebuchet

    But BA, you didn’t mention the chemtrail in the picture! Looks like you’re part of the conspiracy.

    Seriously, why don’t I ever see stuff like that? Guess I need to get out and look up more.

  4. Dan

    The “little blue gizmo” is just a lens flare, isn’t it?

  5. I believe the “blue gizmo” is an internal lens flare. They’re always directly opposite the bright source through the optical center of the lens.

    – Jack

  6. Dang, I see Dan beat me to it…

    – Jack

  7. JSug

    I’ve actually seen this effect quite a lot here in the Seattle area. Chilly autumn nights are a great time to catch it.

    And yeah, the blue spot looks like a lens flare from the reflection on the tube.

  8. TheElkMechanic

    The blue spot is probably a lens flare or internal camera reflection. The Moon Dog is below and to the left and looks like a little rainbow.

    Either that, or the blue spot is a UFO taking pictures of the chemtrail…

  9. Rachael Beaton

    The blue spot is in fact lens flare, which probably is connected to the UV filter I had on my lens at the time.
    I’m glad the terrible observing weather in Charlottesville has *some* advantage :p!

  10. Gary Ansorge

    Back in 1997, I was staying with a friend on top of Grizzly Peak, just above UC Berkely. There was a lot of low hanging moisture/fog that night and I saw a triple moon halo. The moon appeared to be at the bottom of an opalescent tunnel, with the first and brightest nearest the moon, the secondary just outside the primary and appearing closer to me. The third halo was so dim, I could really only see the brightest colors. The darker colors faded to invisibility. It was the coolest thing I’d ever seen around the moon.
    I have yet to see a triple halo around the sun.

    GAry 7

  11. IVAN3MAN, those are some absolutely gorgeous photos! Thank you!

  12. IVAN3MAN, those are some absolutely gorgeous photos! Thank you!

  13. Yay! Glad that we could bring back good memories :-)

  14. Whenever I see a moon halo (three times in my life) I’ve often wondered if I were observing, say, Jupiter at that apparent size – how far away from it would I be?

  15. Leonardo

    Wow…what a coincidence. I saw a moon dog for the first time two nights ago. Wonder if the picture was taken on the same night. (I’m in North Carolina, so not too far away from UVa).

  16. That’s really nice Phil! I remember seeing one once from a plane as we were just taking off. Didn’t have my camera handy…

  17. Rachel’s a great person! She was our speaker at CAS’s August meeting. Her talk topic was “M31 dwarf galaxies: Halo Substructure Research Group” and was absolutely superb!

    (Nicole’s no slouch either! :-) her topic was “Search for the Epoch of Reionization: The Return to Low Frequency Radio Astronomy”)

    Here’s another image of the 6″ Clark (on a Sagemuller hand-wound clock drive mount BTW) for those of you who really dig old scopes.

    The same (but larger) image in a new window.
    Rich in Charlottesville

  18. George E Martin

    Not about moon halos or moon dogs. Just curious if the shed which contains the 6 inch (Alvin Clark and Sons) is still called the doghouse? Also did they ever replace the 8 inch (Tinsley?) reflector which really wasn’t very good?


  19. A while back I was listening to WGBH Boston, to a music critic talking about Schubert’s Winterreise, the song “Nebensonnen”, when he referred to the line, “I saw three suns” as “phantasmagoric”. I wanted to get on the horn and chew the fool out: it’s exactly in late autumn, at least in the North East, when you’re most likely to see sundogs, and if the sun itself is obscured just so by clouds, the it and its dogs can easily look equally bright.

  20. Naomi

    Oooh, I saw one of those rings around the moon on my first night in Flagstaff! (I had been in the US for *counts* six days, and all of those so far had been in LA.) Didn’t show on the photo, unfortunately. This was the 18th of February, around 8 or 9 PM.

  21. kuhnigget

    Token rube story:

    When I was a kid back in Yakima, Washington, where icy cirrostratus clouds are common in winter, I remember one night when the halo around the moon was especially bright, almost as bright as the full moon itself. I don’t recall if there were any moondogs.

    Anyway, the next morning, a local talk radio show we always listened to was inundated with phone calls from people convinced the end was nigh because of the “sign from god” the previous night. Being the snotty kid that I am, er, was, I called up and explained the true nature of the phenomenon. While the host of the show himself was grateful, the rest of the hour was filled with angry callers denouncing the uppity kid who thought he was so smart.

    There was a total eclipse of the sun a few years later…I don’t think I listened to the talk shows then.

  22. @George E Martin:
    Yup, it’s still called the doghouse!
    Rich in Charlottesville

  23. John

    Haha funny story, people can behave so simple at times it’s almost unbelievable.

  24. It was awe-inspiring, to see impact remnants larger than Earth, knowing that impacts like that on our own planet would have wiped us out as a species.

    Hmmm.. somebody should write a book about stuff like that….



  25. Mark

    Nice shot! I’ve seen sun dogs, but never this moon variety.

    “Anyway, the next morning, a local talk radio show we always listened to was inundated with phone calls from people convinced the end was nigh because of the ‚Äúsign from god‚ÄĚ the previous night.”

    Ouch. There goes the neighborhood… It’s a good thing that common sense and education has improved since, and all you sensible folks on the other side of the big pond don’t let those doomsday fans near guns, or, heaven forbid, weapons of the nuclear kind, right?

    Cricket. Cricket.



  26. KC

    Well, I’ll be. So *that’s* what a moon dog/sun dog is. I’ve seen sun dogs before, and figured it was ice crystals in the upper atmosphere forming a nice rainbow effect, but didn’t know what it was called.

  27. Drew
  28. ioresult

    BA said: “where your mind wanders”
    Man, you’re getting old!

  29. Saw a spectacular “moon dog” one time while I was flying over Greenland about a decade ago. For a sec my co-pilot thought he was seeing things, and didn’t say anything about it.

  30. As others have pointed out, the bright blue spot is possibly lens flare, coincidentally on top of the halo. However, below and to the left is a bright rainbow-like spot, and that is the moon dog, I believe.

    IVAN3MAN mentioned “click on [his] name” and see a better moon dog image. For those who didn’t, and/or aren’t familiar with the Atmospheric Optics website, check out all the photos, along with <warning>scientific explanations</warning> of what causes them. (Along with all of the “so that’s what they’re called” information as well. Anyone seen some anti-crepuscular rays lately?)

  31. Surely someone will latch on to that beautiful photo and show that the blue gizmo/lens flare is in actual fact proof positive of an alien spacecraft!

  32. Thanks, Richard. :-)

    George, yup we love calling it the Doghouse. 8-inch Tinsley, is that up at Fan Mountain, now? The Doghouse now houses the 6-inch and a 10-inch Celestron with Autostar. The latter is nice but can be pain to setup, so I still prefer the 6-inch.

  33. Yojimbo

    And, on another tack…. keep an ear open for the Moondoggies :)

  34. Speaking of old scopes, we at CAS (along with a huge load of work by Jim Barr of the Astronomy Department) are slowly working on the Cooke Astrograph up at Fan Mtn. It was a really cutting edge instrument in its day, but it’s seen better days.

    The mount is a big honking equatorial and is getting a new drive motor, but the Cooke’s optics have a great deal of CA (chromatic aberration for you non astronomers out there) which makes imaging tricky. We’re experimenting with notch filters to cut out all the colors but green.

    The only Tinsley I knew of up there was the 30″. I don’t know anything about the 8″ Tinsley, though, Nicole. What’s its f ratio? Maybe Dr. Majewski can use the Tinsley’s optics (if the Cooke doesn’t work out) for the tidal tales work he has in mind… He needs something optically fast, IIRC…

  35. Josh L

    You may be an astronomer but you are not naturally nocturnal. Moonbows-moondogs are not that uncommon but incredibly cool. As others have mentioned There can be double and triple moonbows and they fill up the sky. They are an emotional wondrous night time show.

    Winter is coming and colorado/boulder is a great place to see them. Stay up on those cold long nights winter when the moon is full and you may see one or more. They are incredible things.

    I’n not diurnal so I’ve never seen one around the sun much less a double or triple.


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