formed by algae imaged
by Marko Riikonen (site)
on Tvärminne Longskär Island, Finland.
shown with permission.
Coronae, more familiar as coloured rings
around the moon, are made
when light is scattered, diffracted, by small droplets or particles.
The scatterers need not be transparent and airborne pollen makes excellent
Here, algae of the genus Nautococcus on the pond surface are scattering
sunlight. The cell shape protruding from the water is hemispherical
and this produces oval coronae. The apparent brightenings are most
likely parts of bands produced by another interference phenomenon,
More on algal optics by Marko Riikonen