Circumzenithal Arc Visibility

Many of the ice crystal haloes are sensitive to the altitude of the sun because they depend in some way on the orientation and shape of the crystals. Graphs can be drawn showing the times of day and year when it is possible to see them, provided suitable ice crystals are available of course!

The diagram below shows when a circumzenithal arc may be visible from London. It was created using GraphDark, free software available on another part of this site.

Time of day runs from bottom to top while days of the year run from left to right. The altitude of the sun is colour coded into bands at 5 degree intervals. Light blue indicates the sun is too high while the darker blues are when the sun is below the horizon. Click the summary image to get the full detail.

For London the circumzenithal arc can be seen at any time of day during the winter months. In summer it is only visible in the early morning and late afternoon.

For more details on producing this diagram click here