Algal Glories

Marko has made an intensive study** of optical effects from pond algae. Here he pictures two glories produced by Chromophyton algae floating on pond surfaces.

His camera shadow marks the antisolar point and the glory centres. The glories blaze with the same shimmering rings and colours as their cloud and fog droplet counterparts.

Unlike coronae, glories need at least partially transparent globules and roughly spherical shapes for they are formed by wave paths that travel and reflect inside the scatterer. Chromophyton oblige with some transparency and their globular portions are conveniently raised on stalks free of the water surface. Marko�s microscope image taken in a sideways direction shows the stalks holding up the globes.

A glory's angular size is almost independent of the scatterer's refractive index. The Chromophyton glories indicate (using a homogeneous internal structure assumption) a cell diameter of 5-6 micron consistent with microscopy.

Not shown here but visible on other images, brightenings sometimes occur on the second ring. Marko attributes these to the effects of the distribution of chloroplasts (the green light collectors) within the cell. Interestingly, these change their distribution with light intensity and sun position and cause the cell to deviate in behaviour from that of the homogeneous spheres of fog and cloud.

**Marko Riikonen, 'Optical phenomena from algal films on the water surface', M.Sc., University of Helsinki, 2008.