Across
1
Substance with pH below 7
3
Our home planet
4
Smallest unit of an element
7
Blocking of light by a celestial body
8
Ball of burning gas in space
11
Fourth state of matter
Down
2
Tissue that contracts for movement
5
Positive particle in nucleus
6
Form of thermal energy
9
Second lightest element
10
Curved glass that refracts light