Aureole around Venus

Venus Aureole/Corona

Venus near the Pleiades is covered by a fortuitous cloud wisp that generates a red rimmed aureole/corona. At far left is Orion the Hunter. At his feet Rigel also shows an aureole.

An image from the Tihany Peninsula, Hungary by Tamas Ladanyi (astrophoto.hu). A single image with no colour processing.

The wooden pole structure is a shadoof for raising well water.

©Tamas Ladanyi, shown with permission

Scattering by a spherical particle

Light is mostly scattered from the periphery although some internal scattering occurs for transparent media. For simplicity and clarity the diagram has light scattered from just two points. The outgoing spherical waves overlap and interfere to produce in the far field a corona.

Aureoles & Coronae

Both are diffraction effects. Light scatters, diffracts, from small atmospheric particles - dust, cloud water droplets, pollen grains. When the scatterers are of the same size we see a multi-ringed corona. A wide size range gives an aureole. Somewhere betwixt the two extremes the aureole develops a red edge as here.

The scatterers here - cloud water droplets or ice crystals - are relatively large because the aureole is small. Smaller particles would be needed to make a noticeable aureole/corona around the moon or sun. Conversely, the large coronae seen around the moon would be exceeding rare around Venus because they would be too faint and diffuse.

From almost point sources like Venus or Jupiter we sometimes see oval aureoles. The scattering particles making those have some alignment in the clouds and present a non circular cross section to the incoming light waves.