Bishop's Ring and Aerosol Scattering

November 30, 2012

Trzicky_Bishop-ring (2)

Photographer: Tomas Trzicky; Tomas' Web site  
Summary Author: Tomas Trzicky

The two photos above, taken from Prague in the Czech Republic, show different appearances of the sky near the solar disk caused by the scattering of light from different types of aerosols. The photo on the left was snapped on April 10, 2011, when a fine Saharan dust layer resided over central Europe. The diffraction of sunlight by small dust particles in the upper atmosphere produced a Bishop's Ring -- a large and slightly colored aureole around the Sun with a bluish inner and brownish outer rim. Note that the sky had a rather whitish tint due to scattering of sunlight by these dust particles.

On the second photo, captured six days later on April 16, 2011, molecular (Rayleigh) scattering prevails. This is what gives the blue hue to the clear sky. Only a faint aureole around the Sun is visible. Both images were taken with the same camera settings and at the same time of the day.

Photo details: Canon PowerShot A630 camera; f/8 aperture; 1/2500 sec. exposure time; ISO equivalent 80; metering mode; white balance matrix; daylight; color space sRGB.