Question

why we should not look to the sky, directly at the time of solar eclipse? exact reason

Answer 1

A solar eclipse is awe-inspiring, and the temptation to look at the source of the spectacle can be overwhelming. Solar astronomers and ophthalmologists warn that that's a mistake that can render you permanently blind. It's a warning to take seriously, but there is one time when it doesn't apply. You probably won't hurt your eyes if you peek at the precise moment of totality and look away as soon as the sun reappears.