Friday, 14 May 2010

Odd radius column arcs from Joensuu

Summer's first hot weather spell started on 12 May in Finland, and along came solitary 23° plate arc. Yesterday it got warmer (+24°C) and also the halos got warmer. Odd radius column arcs! In addition to 9° and 24 column arcs (the latter of which always shows as a circular halo) I recognized the 18° column arc in the field, which gave me some satisfaction. 35° halo was visible only through mirror. The 24° column arc was clearly separated visually, but fisheye compresses it close to 22° halo. Should photograph these with normal lens. Click on the above image to see 18° and 20 column arcs marked. There are other images also available; those where sun is behind the lamp are max two minutes stacks, and the sun is not tracked ( 1 ).

There is also, before the odd radius started, photo of parhelia with sun elevation of 33 degrees ( 2 ). Do you think there is something strange? To me they seemed not be on a same level. Although in the photo it may look like the right one is abnormallly high, it was actually the left one that was abnormally low. Or at least that's how it looked. I knew this is hard to photograph because of the lens distortion. Maybe it was illusion. I have seen these things also before, at least in 30.9.1987 display. Also that time it got me rushing to photograph it. But that photo is not conclusive either.

Marko Riikonen


  1. nicolas lefaudeux14 May 2010 at 20:19

    nice! about the parhelia height, you could try to use some software to change the projection of the image to a cylindrical projection and use the streetlight in the bottom right corner as a reference for vertical axis. this way you could check if there is a true altitude difference between the parhelia.

  2. Nice 9d column arcs Marko. Nothing here in USA yet. Early in the year I got weak 9d halo and another day I got high-sun parry and faint wegener arc