As anyone who has experienced totality knows, the difference between a total eclipse and the deepest partial eclipse is not just a quantitative change.<p>At the deepest partial phase, you see Baily's Beads and the Diamond Ring. This is still the sun's photosphere peeking through the moon's valleys, bright enough that it washes out the corona, and bright enough that you had better use eye protection. Only when the moon completely blocks the photosphere do you see the solar corona.<p>This is totality. This is where you no longer need (and can't use) the protective glasses or filters or pinhole projectors. During totality, you can view the corona with your own eyes, with no protection, and even with binoculars.<p>The difference between a 99.9% partial eclipse and a 100% total eclipse is not 0.1%. It is infinity.