Across
1
Nerve cell in the brain
4
Measure of matter in an object
5
Second lightest element
6
Mass per unit volume
7
Icy body with a tail near the sun
8
Blocking of light by a celestial body
Down
1
Center of an atom or cell
2
Unit of energy
3
Curved glass that refracts light
9
Gas form of a liquid
10
Magnetic metallic element
11
Unit of heredity
12
Hottest planet in solar system
13
Tissue that contracts for movement