is there a way to make the grid longer?
 

I'm trying to do a tutorial about Solar System and it turns out that I need to move planets further to the positive x ax, I've moved five planets so far, but where I need to put the sixth, I can't do that, because there's no grid anymore... can anyone please help me on this? Or should I just move plante s not so far away from each other?

You can change the grid in the display options to whatever you need.

If you mean that you cant see the grig after a cirtian difference then select the perspective camera then upp the far clipping plane.

Or to make it more managable it may be best to not make it to scale, depending on what you need the final images for.

Cheers

Steve