Venus Corona imaged December 9, '08 by Tamas Ladanyi (TWAN). ©Tamas Ladanyi, shown with permission.
Venus and Jupiter are in conjunction over the moonlit Szarvasko Castle, Hungary. Bright Venus, to the left, is enveloped in a corona.
Coronae form by diffraction from small droplets in fogs, mists and clouds. Those around the Moon are fairly common but ones around a planet are rare because they are usually too faint to perceive.
Here, we can even estimate the sizes of the droplets producing the diffraction. The star RT Capricorni was 0.81° from Venus, setting the angular size of the aureole red edge. Comparison with Mie scattering simulations in IRIS then give the droplet diameter as about 50 micron or 0.05 mm - at the upper end of the 1-100 micron range of cloud droplets.