An Oval Circumscribed Halo and 22° Halo was observed from the Hollin Meadows Swim & Tennis Club, Fairfax County, Virginia USA.
The circumscribed halo is typically a brightly coloured oval around the sun. It is tangential to the inner 22° halo directly above and below the sun and is brightest there. Sometimes local brightenings of the 22° halo are the only sign of it. Its shape depends very much on the solar altitude. Source Credit: Atmospheric Optics.
I used a fence post to block the disc of the Sun and shot the photos at -3 exposure value (ev). The camera LCD was so dark it was like looking at the Sun through welder's glass! Photo 2 (of 2) also shows a contrail.
 |
| Photo 1 (of 2). |
 |
| Photo 2 (of 2). |
Halos and other types of atmospheric optical phenomena are caused by high altitude cirroform clouds such as cirrostratus. Cirroform clouds are composed almost entirely of ice crystals. Sometimes the ice crystals are the right shape and in the right orientation to cause optical phenomena such as the halo shown above.
Tech Tips
The preceding photos were taken with my Panasonic DMC-FZ150 superzoom digital camera, using the following settings: ISO 100; focal length 4.5mm (25mm, 35mm camera equivalent); -3 ev; aperture f/8; shutter speed 1/2,000 second.
Related Resources
- Halo Phenomena | International Cloud Atlas - World Meteorological Organization
- What Causes Halos, Sundogs, and Sun Pillars? - National Weather Service [USA]
- Atmospheric Optical Phenomena (except Rainbows and Aurora) - Colorado State University [USA]
- The Formation of Snow Crystzls - American Scientist
- A Guide to Snowflakes - Caltech [USA]
Copyright © 2025 by Walter Sanford. All rights reserved,
No comments:
Post a Comment
Comments are invited and wlecome.