A total eclipse, with a partial failure: Scientific expeditions don't always go as planned

For centuries, astronomers have realized that total solar eclipses offer a valuable scientific opportunity. During what's called totality, the opaque moon completely hides the bright photosphere of the sun—its thin surface layer that emits most of the sun's light. An eclipse allows astronomers to study the sun's colorful outer atmosphere and its delicate extended corona, ordinarily invisible in the dazzling light of the photosphere.