Across
1
Positive particle in nucleus
3
The Red Planet
4
Second lightest element
8
Nerve cell in the brain
10
Form of thermal energy
13
Gas form of a liquid
Down
2
Blocking of light by a celestial body
5
Substance with pH above 7
6
Force that attracts objects together
7
Precious yellow metallic element
9
Path of a planet around the sun
11
Natural satellite of Earth
12
Biological catalyst