Monday, 1 June 2020

Odd radius display at low sun in Berkshire, UK

11-frame stack at sun elevation 2°: unsharp mask and colour enhancement (top), and background subtraction + blue-minus-red colour subtraction (bottom; the latter by Nicolas Lefaudeux).

In the evening of 24th May 2020, a notable display of odd-radius halos and their associated plate arcs occurred in Berkshire, UK. I first noticed faint traces of circular halos - 20° and 23° as I could later confirm from photos - at around 19:20 BST, when the sun was at 13° elevation. Less than 30 minutes later the sun had come down to 9° and first signs of the upper 20° plate arc appeared, making obvious the need to find a view down to the horizon. The display got weaker after some time but regained some intensity less than 30 minutes before the sunset. Unfortunately there were some lower-level cloud interfering with my view for most of the observing time.

Stacked and further processed images from the first stages of the display (below) reveal 18°, 20°, 23°, and 35° circular halos in addition to the aforementioned 20° plate arc. At the end of the display (above), the circular halos are less clear, but plate arcs at 20° and 35° show up better. Most interestingly, perhaps, there are suggestions of 28° circular halo and the associated plate arc at the upper left-hand side at solar elevations 7° and 2°. Previously 28° arcs have been reported in the Lascar display of 1997 and in a few more recent occasions in China, but possibly never before in Europe.

50-frame stacks at sun elevation 9° (top) and 7° (bottom): Background subtraction (left) and background subtraction + blue-minus-red colour subtraction (right).


  1. I can see a 28d halo very clearly in the stacks. I hope to get one some day where its naked eye visible along with its arcs

  2. Congratulations Reima! Finally the same 28d stuff are spotted in Europe!It seems there's a good chance that they lurk in weak, low-sun plate displays like this one.

    Too bad there're still no associated exotic arcs observed. It's getting kind of weird that all these recents cases essentially look the same. Hope we'll get a more intense and long-lasting display in the coming months.

  3. interestingly also, with the halocamera, that had been running for years 2014-2018 in Paris, i captured a handful of OR displays where there seemed to be traces a 28° halo. none were clear enough to call it a catch, yet, all of them where at low sun.
    together with the chinese cases and Eresmaa case, i am now starting to think it might be worth unearthing those possible cases.