Why You Can't See The Moon During A Total Solar Eclipse
“There are some astronomical observations, even with a powerful telescope, that can only be made with the help of photography. To gather enough light to stand out against the brightness of other objects is something that goes beyond what human eyes can deliver. Thankfully, that technology is widespread today, and enables us to enjoy a whole slew of sights our eyes cannot deliver. It may be dark during the eclipse, but darkness, as we perceive it, is relative. Our Sun's corona, during totality, will become the brightest thing in the sky, and is the reason the Moon, to human eyes, will be completely invisible.”
During those moments of totality, the Sun is eclipsed by a new Moon, with the latter’s shadow falling onto Earth. From within that shadow, the Sun’s disk is blocked entirely, revealing a slew of fainter objects: stars, planets, and the Sun’s corona, all of which cannot normally be seen during the day. Yet one object even brighter than all the stars -- the new Moon -- will remain invisible throughout the eclipse. Despite the Moon acting as the ultimate coronagraph, blocking out 100% of the Sun’s light, and despite the full Earth reflecting its light back onto the Moon, you won’t be able to see the lunar surface at all. Why is that? It’s the relative brightness of something very close by: the solar corona. Even though the Sun’s corona is some 400,000 times less bright than the Sun, it’s still ~10,000 times brighter than the new Moon, enough to render it totally invisible to human eyes. It’s like trying to see a firefly an inch away from a shining light bulb, when you’re standing 20 feet away.
In short: the corona is too close and too bright, and that’s why the Moon is only visible in photographs.
