Thursday, 9 July 2009

119 pages of streetlight halos

The days are shortening and winter is coming soon. What a better way to get pumped for the upcoming diamond dust season than reading Walt Tape's 119 page treatment on spatial halos. New effects like superparhelic circle await for their discoverers. About half of the contents is the old stuff that you may have read already, but Walt has made some changes, so it is not bad idea to go through those parts as well.

Click on the image to go Walt's page to download it.


  1. Walt's latest contribution to halo science is nothing short of fantastic! These insights indeed have a profound effect in the way we understand "classical halos" as well.

    The sensation of standing in the beam, observing the billions of crystals sparkling in the light, has now got a worthy theoretical companion.

    I hope to see this stuff in book form soon. Seminal work.

  2. marko riikonen9 July 2009 at 14:21

    And we can give our little contribution by trying to take good photos of these effects.

    Hmh, "billions of crystals" made me think of how much actually there are crystals in an average snow gun diamond dust per, say, cubic meter?

  3. Hardback edition please :)

    For me the streetlight halos are the whole new world what I personally haven't dealt with jet. Respect towards people who observe, research and explain this phenomena.

  4. Quite a few I would think. See video (1)

    Perhaps in the order of thousands. If we think about a fifteen minute observation with a bright, high street lamp that illuminates a large area the numbers will add up.

    Sometimes the number is probably in the order of tens of thousands when the swarm is extremely thick. See video (2).

  5. jukka ruoskanen9 July 2009 at 18:27

    Walt has a solid comprehension for complex 3D geometries in space. This pdf-file is a serious package which takes a while to sink in. Halo geometries are truly pretty. This work contains novel viewpoints, and it presents an exciting challenge to understand fully what is going on - to be able to imagine these geometrical mechanisms in one's head. Moreover, this work makes me anxiously wait for the winter.

    Some papers that I've read suggest that the ice crystal number densities up in Cirrus clouds can reach values up to 50 million per cubic meter. The variations are large, of course, and the minimum values have been in the order of a few hundred thousand. Maybe Jari's estimation is quite close for typical snow gun displays, but I'd imagine the most severe crystal swarms must reach millions.

  6. Thanks for the info Jukka. I tried to err to cautious side.

  7. Thanks for sharing this incredible work with us, Walt! I'm really looking forward to reading the whole. You are creating an entirely new perspective in halo science.

  8. Thanks, Marko, for the advertisement. As for the superparhelic circle, yeah, it should be out there, ripe for plucking by the prepared and persistent observer. But let's remember that it was Lars Gislen's simulations where it first showed up.

  9. Thank you very much for this valuable work! It's a very good job!

  10. I can't wait for the cold weather myself being I have the paint gun. I not onlyy have my spotlight but for a divergent light source I got a powerful floodlight.