The moon is not a perfect sphere!  It has mountains and valleys.  The Sun peeks through at those points and looks like little beads.  This happens moments before totality 

The last of Bailey's beads appears bright and looks like a diamond ring.  This happens an instant before totality

The Sun's atmosphere is called the Coronasphere.  It can only be viewed during a total eclipse.  If you look closely you may be able to see solar flares.