Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2012 June 23
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Northern Green Flash
Image Credit & Copyright: Göran Strand

Explanation: As seen from Frösön island in northern Sweden the Sun did set a day after the summer solstice. From that location below the arctic circle it settled slowly behind the northern horizon. During the sunset's final minute, this remarkable sequence of 7 images follows the distorted edge of the solar disk as it just disappears against a distant tree line, capturing both a green and blue flash. Not a myth even in a land of runes, the colorful but elusive glints are caused by atmospheric refraction enhanced by long, low, sight lines and strong atmospheric temperature gradients.

Tomorrow's picture: moon stop

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