4 Dec 2002 Jarmo Moilanen

Observing halos

Observing Halos

Halo observing is quite trivial. There is no necessery equipment. Dark sunglasses are however a good aid to prevent sun glare. A convex mirror is sometimes usefull. Also notepad with pencil for recording different stages of the display are really good help.

Camera should be used always there are bright or unknown halos in the sky, preferably always. Photographs have scientific value at least if their time and lens focal lenght have been recorded. Only slide film should be used in halo photographing. 100 ASA is usually most reliable. Diminish an exposure or two from camera lightmeter values - s/500 at f22 for solar direction and s/125 at f18 elsewhere give a somewhat good basis for exposure experiments.

Printable FHON observation forms in English

• A-form (a list form) for all displays and common halos*
  • A4-sized (52 kt PDF)
  • letter-sized (51 kt PDF)
• B-form for displays with rare halos
  • A4-sized (10 kt PDF)
  • letter-sized (10 kt PDF)

*) Common halos listed in A-form: 22° halo, sun pillar, (22°) parhelia, 22° tangent arcs, circumzenithal arc, circumhorizontal arc, 46° halo, (46°) supralateral arc, parhelic cirlce and subsun. Althought circumzenithal arc and circumhorizontal arc are same halo, they are listed separately because this way it is easier to separate high sun displays from low sun displays.

These forms need Adobe Acrobat Reader -program, which can open and print these forms. A free copy of Acrobat Reader -program can be download from Adobe homepage:

A brief filling information of forms 

In A-form you should write down details for every display (day, time, place etc) and mark all boxes of common halos you see. If you see a halo in display which is not listed in A-form, mark B-form -circle in the end of common halo form boxes and fill am extra B-form with detailed information of the display and rare halos.

In addition of writing down informations of halos and marking all observed halos in A-form, you should also make drawings of displays. It may help revaluation of some old displays if you have drawings fo them. Those drawings are better to do on plank paper instead of backside of form. In B-form there is already one box for drawings and a circle for all sky drawings.