Actually, if the comet or asteroid was coming from the direction of the sun, we probably wouldn't see it. In order for it have escaped our notice on its approach it would have to be a fast moving extra solar object that swept in from the other side of the sun from us, slipped past the sun on a close fly by, and would be speeding toward us with an extremely high velocity. It wouldn't even have to be that big at those speeds to do a whole lot of damage... Big being a relative word, of course. Except if it was of fair mass, moving at relativistic velocities... It would have a strong gravitational pull... So, we'll probably feel its effects on Earth before it arrives... earthquakes, storms, floods.
Interesting, never thought of it that way before.
Hurricanes????!!!!
lol