Message text written by INTERNET:[EMAIL PROTECTED] RE Circumzenithal Arc
>This sounds interesting... the sun is in that range here as we speak. Could you fill me in on what I'm looking for, and the conditions (time of day, weather, etc) necessary? < I've attached a JPG that pretty well shows the sky conditions. It is only of a partial arc, but it gets the idea across. The time of day? Well, when the sun has an altitude of between 18-26 degrees above the horizon. The time depends on the time of sunrise and sunset. I start looking from 3 hours after untll 4 hrs and 20 minutes after sunrise. I look again from 4:20 before sunset until 3 Hrs before sunset. (I think my math is correct, but...) I use : Solar Hour Angle = 18 degrees /sin(23.5) (45.14 degrees HA - 3 hours) and : Solar Hour Angle = 26 degrees /sin(23.5) (65.2 degrees HA - 4:20 ) I'm including lines on my sundial to show when the sun is between these altitudes. Please forgive me for attaching the JPG, but I didn't think it was too big. I got it from "The Audubon Society Field Guide to North American Weather". They have a good amount of info on solar refraction/reflection phenomenon. It's a great book if you have any interest in the weather and clouds. The pictures are fantastic! Chuck. Attachment converted: MAC Hard Disk:zenarc.jpg (JPEG/JVWR) (0000F820)
