> The Earth has its own gravity
> and there's a point at which it
> becomes stronger than the Sun's
> or we'd all be falling into the Sun!
Nope, we all ARE FALLING into the sun, we just keep missing it. That's what an orbit is. If we could stop the Earth and hold it still everyone sun side would fly off the Earth into the sun. The Sun's gravity is stronger.
Anyways for nightfall to block out the sun it would have to be too far past the Earth to ever come back.
However you could have two rocks, the first which is spotted and we know will miss but as it gets closer we discover it was blocking our view of a second that will indeed hit the Earth.
The first is the one that blocks out the sunlight and the second the one Superman has to stop.
But hitting it is still a poor idea. We could have him hit it with his ship, flying it up and using it like a wedge.
Or we could have him push it faster so that it misses the Earth arriving to the intersection point of Earth's orbit much earlier than the Earth and thus mssing the Earth.
And that would be easier than smashing it or pushing it off course.
