Newsgroups: rec.aviation.student
Subject: Re: Rainbow
From: jbolinger@lintek.com (J L Bolinger)
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In article <362dddb9.0@news.map.com>, mregish@map.com says...
>
>All rainbows are complete circles with the center point being on a line from
>the sun through your eyes, ie., the sun has to be directly behind you and
>the water drops forming the rainbow in front of you. The only reason we
>don't see the complete circle from the ground is that the horizon is in the
>way. When you're up in a plane, you can see the full circle. You can make
>your own rainbows using this info by placing the sun at your back and
>spraying a fine mist in front of you with a garden hose. You will see a full
>rainbow. When you see your shadow from the air inside the full circle of the
>rainbow, it is because there are water droplets between you and the ground
>and the sun is behind you. The shadow HAS to be in the center of the rainbow
>to meet the conditions to form the rainbow.
>
>I haven't seen this from the air yet, but I've been looking forward to it.
>If you're flying towards the rainbow, you can expect to eventually fly into
>some rain, depending on how far away it is.
>
>--


I didn't see the original post that started this thread, but here are
my comments anyway.

If you are located between the sun and the rain/mist, the colors of the
rainbow will be 'normal'.  If the rain/mist is located between you and
the sun, the colors will be reversed.  This phenomena, known as a sun dog
usually occurs as a small patch of light exactly 22.5 degrees either side
of and at the same elevation angle as the sun, usually when there is a
thin cloud layer.  This is actually quite common here in central Ohio, but I
probably notice things like this more than most people.  Sometimes the
clouds mix up the colors and it appears as a white patch of light.


By the way, the angular width of a complete rainbow is exactly 45 degrees.
This results from the geometry of the defraction of the light inside a
spherical water droplet.  The sun also has to be at the correct height
above the horizon for both rainbows and sun dogs to be visible.  That is 
why they are seen only in the mid to late afternoon.

Jim

