Across
1
Blocking of light by a celestial body
5
Form of thermal energy
6
Nerve cell in the brain
7
Particle of light
8
Magnetic metallic element
12
Curved glass that refracts light
15
Element found in all living things
Down
2
Mass per unit volume
3
Push or pull on an object
4
Substance with pH below 7
9
Biological catalyst
10
Substance with pH above 7
11
Path of a planet around the sun
13
Unit of energy
14
Positive particle in nucleus