Across
1
Second lightest element
4
Particle of light
6
Center of an atom or cell
7
Nerve cell in the brain
10
Icy body with a tail near the sun
11
Disturbance that transfers energy
12
Tissue that contracts for movement
Down
2
Push or pull on an object
3
Preserved remains of ancient life
5
Naturally occurring inorganic solid
8
Substance with pH above 7
9
Blocking of light by a celestial body
13
Ball of burning gas in space
14
Gas essential for breathing