Answer:
I'm a god. I'm a planet. I measure heat.
I'm white, I'm round, but not always around. Sometimes you see me, sometimes you don't.
With sharp edged wit and pointed poise. It can settle disputes without making a noise.
I am free for the taking. Through all of your life, though given but once at birth. I am less than nothing in weight, but will fell the strongest of you if held.
When you stop and look, you can always see me. If you try to touch, you cannot feel me. I cannot move, but as you near me, I will move away from you.
When is it bad luck to see a black cat?