The diamond ring effect is a feature of total solar eclipses. Just before the sun disappears or just after it emerges from behind the moon, the rugged lunar limb topography allows beads of sunlight to shine through. This effect is called Baily's beads, in honor of Francis Baily who first noted the phenomenon in 1836.
The smoothness of the lunar topography is interrupted by mountains, craters, valleys, etc, and the lunar limb profile is known accurately from grazing occultations of stars, so it is possible to make fairly good advance determinations of which mountains and valleys will cause the beads to appear. While Baily's beads are seen for a few seconds at the central path of the eclipse, they are visible longer near the margins of the path of totality.
- Report on the Total Solar Eclipse of 1998 February 26.
- What to See During an Eclipse Continued.
- Baily's Beads visible in an eclipse of a light source by the Apple logo.ar:حلقة ماسية