Blue spot gets more colours

 

Blue spot is the colour feature of the parhelic circle occurring at the anthelic region of the sky. In addition to the blue, the theory predicts also green, but no red. Yet in several observations also red colour has been reported. However, because the red has never reproduced in photos, the observations have been doubted.

The image here shows two versions of a simulation of plate crystal parhelic circle in the anthelic region of the sky. The upper one has not been processed, the lower one has an overall levels adjustment to enhance colours. It looks like there is red present in addition to blue and green.

So it may be that observations of red may have not been wrong after all and that the theory (and naming) of the blue spot needs to be reconsidered. Lacking of the red in photos may be explained by film and sensor sensitivity issues. Even though the colors are seen with naked eye, they are still weak and some wavelenghts may be more prone than others to be not captured by the photographing equipment.

The simulation was made with a software developed by Jukka Ruoskanen. Sun elevation for the simulation is 25°, the plates have aspect ratio of 0.9 and tilt 3°.

 

by Marko Riikonen

 

Original post in Halo reports

The Beginning of Halo Season in Hungary

The halo-season in Hungary has began in a very promising way. There were two particularly noteworthy displays this week. 

The first one was observed by László Henez "Felhőcske" on 16th September near Eger, Hungary. As a born halo-observer, even though he was quite unaware of what he was seeing, he took a picture of not only the sunward halos, but the anthelic side, as well, where about a quarter of the bright white parhelic circle was visible together with a Wegener arc curving downwards towards the anthelic point. The 22° halo and the upper tangent arc were seen in the sky covered with uniform Ci for about half an hour after 8:25 UTC, while the anthelic arcs for only a few minutes. László did not see any 120° parhelia or anthelion. More of László’s photos can be seen here.

In the afternoon of 18th September, an odd radius display appeared with pyramidal 18° and 9° halos besides the 22° one. The photo was taken by "Controll" in Jobbágyi, northern Hungary, but the 18° halo was seen in Budapest by Alex Farkas, too. The display started with a 22° halo and lasted for roughly 40 minutes, until 14:15 UTC. "Controll" reported that she had seen a possible 46° halo as well, but it was at the edge of visiblity. It’s worth having a look at the faint pyramidal crystal parhelia in the picture provided. The full-size photo is also available, together with a panorama image of the display.

By Ágnes Kiricsi