[Allan Scahill]

Allan Scahill  asked the Naked Scientists:
   
Hello Naked Scientists:

I have just finished listening to a podcast from August of 2009.

Dr. Dave Ansell responded to a listener who had a question about rainbows. Dr. Ansell mentioned that rainbows can be seen at an angle of 42 degrees from the sun and when you are at altitude and that rainbows can't be seen as a circle.

I'm not sure if these fall into the category of rainbows, but here in north America we get a phenomenon called "sun dogs". I don't know what the scientific term is.

You can see these circular "rainbows" on either side of the sun and it usually happens in the winter or if the air far above is cold. The "rainbow" is a ring around the sun and more clear on either side of the sun. I don't know if the "sun dogs" constitute a rainbow, but they do form a circle.

A regular listener of both your podcasts
Regards

Allan Scahill
Medicine Hat, Alberta, Canada

What do you think?

[Spannerman]

Sun Dogs form due to ice crystals, these ice crystals reflect the light of the sun making bright spots of light.

I don't think these can be classified as a rainbow as rainbows show/separate all the various visible colours of light whereas the sun dogs only reflect the light.

- Spannerman

[stereologist]

A circumzenith arc separates the light rays, but does not form a circle. It is seen as a brilliant rainbow directly overhead.

[frethack]

On a related note, the Solar Dynamic Observatory (SDO) was launched recently, and the rocket flew straight through a sundog.  Is this irony or what?

Heres the video...its beautiful.
http://science.nasa.gov/headlines/y2010/18feb_coolmovie.htm