Halos in the sky

I just got back from this evening’s Cafe Scientifique — where were you guys? — and I got to see lots of pretty pictures of halos and sundogs and light pillars. One of the nice things about living in Morris is that we actually get a lot of that weird atmospheric phenomena here, because we have lots of the raw material for them here: ice crystals. Vast drifting clouds of hexagonal crystals, flat and columnar, of various proportions, floating in the sky at various orientations to both refract and reflect light into our eyes.

I won’t go into all the details, since you weren’t there. And since most of you live in a less blessed place than the cold crisp upper midwest in the wintertime, you won’t get to see them, because your wicked heat melts all those sharp edged crystals into sludgy droopy droplets. Sorry. But I wanted to pass along one tip.

There’s some free software called Halosim that lets you do simulations of ice crystal distributions in the atmosphere. You specify their sizes and proportions and shapes, and then it traces the paths of light rays and produces an idealized image of what you should be able to see.


It’s very cool. You can tinker and see that to make dramatic sundogs, for instance, you need lots of flat hexagonal platelets floating in a mostly horizontal orientation, and presto, you’ll get a pair of virtual suns 22° to either side of the real one.

Well, maybe you can do that. It’s PC only, so I can’t run any of the simulations on my home computers myself. I’ll have to settle for looking at the real thing, darn it.


  1. says

    Weren’t these one suggested cause of the supposed Miracle of the Sun in Fatima?

    Other than the usual misquoted, made up, exaggerated claims a friend of a friend of your great uncle who talked to someone who might have been there but it’s really true, no really, honest cause of course.

  2. StevoR : Free West Papua, free Tibet, let the Chagossians return! says

    NASA has more on that event here :


    NASA’s Solar Dynamics Observatory (SDO), best known for cutting-edge images of the sun, has made a discovery right here on Earth.

    “It’s a new form of ice halo,” says atmospheric optics expert Les Cowley of England. “We saw it for the first time at the launch of SDO–and it is teaching us new things about how shock waves interact with clouds.”

  3. lpetrich says

    You can get VMWare Fusion or Parallels, and they run Windows inside your Mac. Ever heard of the brain-in-a-vat thought experiment? This is the computer version.

    I ran HaloSim just fine using WinXP inside of VMWare. I found the view positioning rather tricky, and the results are dots rather than smooth shapes — I couldn”t figure out how to make the dots weak enough so as to get smoothness when I make a large number of them.

  4. Loud - warm smiles do not make you welcome here says

    @Azuma Hazuki #14

    Who is this OperaArches? I see him spamming that same link all over FtB.

    Worryingly Mabus-esque, isn’t it?

  5. crocodoc says

    In addition to Ipetrich’s suggestion to run Windows in a virtual machine:

    If you don’t have a Windows licence, you can use a free OS and use the API emulation layer WINE to run the program. It works fine for me here (Ubuntu 12.04).

    Someone wrote that WINE is available for OS X, too. That would be even easier but I cannot comment on that, having no experience with any of the world’s most ruthless patent troll’s products.

  6. lpetrich says

    Yes, one can get WINE for OSX. The simplest way to do so is to get Crossover for Mac, some software with WINE built into it.

  7. Scott F says

    It’s PC only, so I can’t run any of the simulations on my home computers myself.

    There are several VM packages that allow you to run “PC” software on your non-Windows computer. My son likes Parallels for the Mac. Most, though, require that you have a licensed Windows OS installed.