Mystery White Spot - Atoptics Highlights OPOD

Seen by John Flude on December 28 over Eastbourne, England. Clues: Near noon, sun far to the left, same altitude as the sun, cirrus cloud.

Image ©John Flude, shown with permission

Hexagonal plate aspect ice crystals in the cirrus cloud made it. The complex ray path is best achieved when the crystals are thick or have alternate sides long and short. We see perfectly regular crystals in diagrams but they are rarely so in nature.

120° parhelia are white and often hard to see. This one was unusually bright. Another unusual feature was the lack of a parhelic circle passing through it.

When you see something unusual note your position, date and time - plus time zone and whether daylight saving time. Keep the camera clock accurate to a known time zone.

Note the position relative to the sun.

If possible take several hand held camera images. This helps eliminate misidentification of lens reflections.

Video is not much use for getting directions and still shots are better. Zooming video in and out and waving the camera about is even worse!

Isolated bright spots far from the sun can be hard to identify. The cirrus patch and altitude the same as the sun were important clues.

Using the photograph and the camera position John Flude carefully measured its spot's position. A magnetic compass near metal and the window was unreliable so this was supplemented by an Ordnance Survey map and Google Earth. The spot's azimuth was 295-300° (roughly WNW)

The image was taken at 11:56 UTC (always have an accurate camera clock for sky phenomena!) giving a sun azimuth of 178.9° (almost due south).

Combining these gives the spot's azimuth from the sun of 116-121°.

Mystery solved - An ice halo. An exceptionally bright 120° parhelion.