Oddly Shaped Suns at Sunset as Viewed From San Francisco

August 13, 2014

Sunspot mirage 1

Sunspot mirage 2
 
Photographer: Mila Zinkova; Mila's Web site
Summary Author: Mila Zinkova

In San Francisco the setting Sun rarely appears round. Due to the atmospheric refraction, not only does the Sun not look round but it changes its shapes constantly even during the same sunset. This phenomenon is called a sunset mirage. This same phenomenon is responsible for beautiful green flashes. Note the green flash on the bottom image -- upper rim of Sun. The green flash was described by Jules Verne:

"…it will be 'green,' but a most wonderful green, a green which no artist could ever obtain on his palette, a green which neither the varied tints of vegetation nor the shades of the most limpid sea could ever produce the like ! If there be green in Paradise, it cannot but be of this shade, which most surely is the true green of Hope!"

These images also show miraged sunspots. The bottom image was taken less than a second after the top one; yet see how different the sunspots look. They're still miraged, but just like with the Sun, the mirage changed their appearance. These sunset mirages are explained by Dr. Andrew Young of San Diego State University as a type of mock mirage formed by inversions with waves on them. He states "The crest of a wave can act like the convex upper surface of an inversion that's completely horizontal, where the convexity is just due to the curvature of the Earth (and, of course, the inversion follows that curve)." This type of mirage can be best seen with a clear view of the distant horizon, such as when looking at the setting Sun from a seashore.
 
Photo details: Top - Camera Model: Canon PowerShot SX40 HS; Focal Length: 150.5mm; Digital Zoom: 3.125x; Aperture: f/8.0; Exposure Time: 0.0006 s (1/1600); ISO equiv: 100. Bottom - Same.