Earliest known use (by me, but certainly may
be predated), soon after the 1976 total solar eclipse. Also see:
http://nicmosis.as.arizon a.edu:8000/UMBRAPHILLIA.h tml
Not only solar eclipses but occultations in general!
When the moon or an asteroid passes in front of a distant star, the moon or asteroid casts a shadow into space and if the earth intercepts the shadow an umbra is created upon the ground. As the shadow sweeps by the observer the star briefly disappears. A Solar Eclipse is realy a Lunar Occultation, it’s just that the star is up close and personal!