Make sure you are building in a new Object Mode.
Venus is 10.8 BUs away from the sun.
Count 10.8 BUs away from the sun and click.
Zoom in so you can count the tenths place.

Venus is .12 BUs.
Click <Add <Mesh <UVsphere
Change the radius to .06. Click Ok.
I added the red lines so that you could see it covers .12 BUs.

