Across
1
Smallest unit of an element
3
Our home planet
4
Blocking of light by a celestial body
8
Center of an atom or cell
9
Nerve cell in the brain
10
Gas form of a liquid
11
Unit of electric potential
12
The Red Planet
Down
2
Ball of burning gas in space
3
Biological catalyst
5
Icy body with a tail near the sun
6
Group of similar cells
7
Element found in all living things