Across
1
Amplified beam of light
4
Gas essential for breathing
7
Second lightest element
9
Naturally occurring inorganic solid
12
Natural satellite of Earth
Down
2
Unit of electric potential
3
Force that attracts objects together
5
Basic unit of life
6
Positive particle in nucleus
8
Blocking of light by a celestial body
10
The Red Planet
11
Disturbance that transfers energy