There is no such thing as an unexpected eclipse - yes, I'm talking to you, Whedon - they can be predicted centuries to thousands of years in advance. The only way to produce one unexpectedly is to move the bloody moon!
You cannot see the moon in the sky next to the sun before an eclipse of the sun starts - the light of the sun drowns out the moonlight completely. You do not see the moon in the sky once the eclipse has started - you just see a circular area missing from one edge of the disk of the sun, which gradually gets bigger.
Eclipses of the sun do not happen suddenly - it takes an hour or more for the moon to cover the sun. For most of that time it will look almost as bright as a normal day, and you will only notice that there is an eclipse if you look at the sun with the appropriate filters etc. There is a window of a few minutes, not several hours, when it actually feels abnormally dark.
Eclipses of the sun are NOT global events - there is a relatively narrow track on which the eclipse occurs, and different places see it at different times as the shadow of the moon moves across the surface of the Earth. Places off the track get a partial eclipse or don't see it at all.
All of this should be obvious to anyone who has ever watched an eclipse. So why the hell do TV, comics, etc. consistently get it wrong?