20 May 2019

Circumhorizontal arc


The Astronomy Picture of the Day:
Sometimes known as a fire rainbow for its flame-like appearance, a circumhorizon arc lies parallel to the horizon. For a circumhorizontal arc to be visible, the Sun must be at least 58 degrees high in a sky where cirrus clouds are present. Furthermore, the numerous, flat, hexagonal ice-crystals that compose the cirrus cloud must be aligned horizontally to properly refract sunlight in a collectively similar manner. Therefore, circumhorizontal arcs are quite unusual to see.

4 comments:

  1. I saw one of these recently when I was in Huron, Ohio, on Lake Erie. An interesting thing is it appeared much larger and more colorful through my polarizing sunglasses.
    When I pointed it out to people not wearing sunglasses they were, understandably, underwhelmed. I didn't realize that until I removed them to take a picture.

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    Replies
    1. The APOD link says "This circumhorizon display was photographed through a polarized lens above Dublin, Ohio in 2009"

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  2. I am not if this is the same, but it was real surprise to see this:

    https://skeetmotis.blogspot.com/2016/06/fire-rainbow.html Fire rainbow

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    Replies
    1. Yup! Same phenomenon. For more information, Atmospheric Optics is the place to go.

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