Inner & Outer Pollen Corona, Sweden imaged by Mats Mattsson (Astro & Atm Optics Site) May 31, '09. ©Mats Mattsson, shown with permission.
Like its namesake the solar corona, an atmospheric corona has a tremendous range of brightness. The combined brightness of the rings is only 2% of that of the central aureole and each ring is much fainter than the one inside it.
A single image has difficulties in coping but here Mats' exposure saved as a RAW file does so. Three versions processed with different 'exposures' reveal the features.
All show the characteristic vertically elongated rings of a pollen generated corona. The image at right best shows the ring brightenings resulting from the asymmetric particles whose air sacs give them a preferred aerial orientation.
The second image captures the delicate straw, pink and red hues at aureole's outer rim. The colours result because longer wavelength aureoles are the larger.
The rings show a whole range of complex hues, complex because there is much colour overlapping.
The lower image reveals the outer structure with at least three and possibly four rings. The processing necessarily flattens the relative intensities of the rings.
Pollen coronae have many rings because the particles diffracting the light are monosized.
Some day we might have 128 bit monitor screens to display better these subtleties.
Formation by diffraction