Across
1
Unit of energy
4
Mass per unit volume
5
Ball of burning gas in space
6
Glass that splits light into spectrum
7
Center of an atom or cell
9
Natural satellite of Earth
11
Icy body with a tail near the sun
Down
2
Gas essential for breathing
3
Naturally occurring inorganic solid
8
Amplified beam of light
10
Element found in all living things