Venus, Jupiter Coronae
in Austria captured the conjunction of Venus, Jupiter and Mars on the morning of 24th October '15. A fortuitous wisp of cloud produced coronae around the brighter planets and even dimmer ruddy Mars has a hint of one (see below).
Image ©Franz Kerschbaum, shown with permission
Mars has perhaps a hint of a corona at 6-8 o' clock.
Cloud, mist and fog droplets produce coronae. Their droplets are small enough (5 - 100 micron across) to significantly diffract light.
Their coloured rings are familiar when thin clouds scud over the moon.
They can be seen (care!) around the sun if it is shielded by a building or pole or reflected in water.
But all light sources produce them and long exposures
will show them.