Meaning of diamond ring effect

dia'mond ring' effect"

Pronunciation: [key]
— Astron. Astron.
  1. a phenomenon, sometimes observed immediately before and after a total eclipse of the sun, in which one of Baily's beads is much brighter than the others, resembling a diamond ring around the moon.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.