Because galaxies are mostly nearly-empty space the stars and planets in the two galaxies don't collide with each other.

Alta predicted that the planets and the moon would collide, with the result that the earth would be pushed out of its orbit and burned by the sun.

The planet ultimately collides with Earth, causing the end of the world at the conclusion of the movie.

In little more than an hour, Picard realized, wormhole and planet would collide.

Everybody knew that in a thousand years the planet, Demeter, would collide with another.

He could cause planets to collide and produce his suns and stars, his heat and light.

How could anyone possibly know that two planets on a collision course would not collide, but merely touch...?

She had no way of knowing that our pasts might always touch, but our planets would never collide.

And then... about 2.1 billion years ago, after avoiding proto-Earth for countless years, these two planets inevitably collided.

Collisions among galaxies are fairly common, but because galaxies are mainly nearly-empty space, the stars and planets in the two galaxies don't collide with each other.