Some Natural Spectroscopy!
Posted: Mon Jan 15, 2018 8:08 pm
The weather here has been quite frigid lately with high temperatures near -20C. Low temperatures and low Sun definitely curtail imaging and observing but, on the plus side, we are occasionally treated to beautiful displays of atmospheric phenomena involving atmospheric ice crystals. Today, we could witness a day-long spectacle of complex arcs associated with refraction (and consequent dispersion) through these ice crystals. Here are two photos of the beauty on display.
It's actually quite hard to appreciate the extent over the sky of the various arcs and halos from photographs alone. The inner circular halo has an angular radius of 22 degrees while the outer "halo" (actually a big arc - the supralateral arc) has a 46 degree radius. That's a lot of sky coverage and is very impressive to witness by eye! I was limited to a 24mmf camera lens for these pics and the cold killed my battery before I could start setting up a panorama.
Here are the names of some of the observed features:
There is a reasonably good description of these at http://www.atoptics.co.uk/ under the topic "Ice Halos".
All of the observed features can be explained by the phenomenon of "minimum deviation" of a light ray propagating through a prism (hexagonal prism in the case of these ice crystals). Arranging the minimum deviation condition can be a useful technique in prism spectroscopy.
Cheers.
Peter.
- IMG_2685_proc.png (672.7 KiB) Viewed 4762 times
- IMG_2687_proc.png (594.67 KiB) Viewed 4762 times
It's actually quite hard to appreciate the extent over the sky of the various arcs and halos from photographs alone. The inner circular halo has an angular radius of 22 degrees while the outer "halo" (actually a big arc - the supralateral arc) has a 46 degree radius. That's a lot of sky coverage and is very impressive to witness by eye! I was limited to a 24mmf camera lens for these pics and the cold killed my battery before I could start setting up a panorama.
Here are the names of some of the observed features:
- IMG_2687_proc_lbls.png (185.57 KiB) Viewed 4763 times
All of the observed features can be explained by the phenomenon of "minimum deviation" of a light ray propagating through a prism (hexagonal prism in the case of these ice crystals). Arranging the minimum deviation condition can be a useful technique in prism spectroscopy.
Cheers.
Peter.
3 dog sun