Across
1
Ball of burning gas in space
2
Center of an atom or cell
3
Group of similar cells
4
Nerve cell in the brain
9
Molten rock beneath Earth surface
10
Icy body with a tail near the sun
11
Compound containing oxygen
Down
2
Unit of force
5
Curved glass that refracts light
6
Unit of electric potential
7
Blocking of light by a celestial body
8
Force that attracts objects together
9
The Red Planet