|High Sun Halos imaged
by Pennina Neumann
(images) during Israel's spectacular display on
March 7, 2007. ©Pennina Neumann.
The previous "Todays Feature" showed the high sun Parry arc and extreme distance from the sun of the sundog during the 'high sun' halo display over Israel. While searching more of Pennina's images for the Parry arc expected beneath the 22° halo, I noticed a trace of another arc on the image at left. Could it be the fabled Lowitz arc? Enhancement by unsharp masking and embossing revealed that it was likely. The arc was then found on three more images. Finally, the comparison with the HaloSim simulation at right confirmed it.
Interestingly, the sun's elevation was almost the same as that in St Petersburg when professor of chemistry Tobias Lowitz first recorded the controversial arc in June, 1790. He also saw only the lower arc. The high sun renders the corresponding upper arc weaker but its failure to show could also be due to plate crystals having only limited rotation about the Lowitz axis. Variable cloud often makes Lowitz arc identification and characterisation difficult. Ideally, many images should be taken with a fixed camera position over a long period followed by comparison of individual images or stacking. But above all, make time to enjoy halo displays!