Across
1
Curved glass that refracts light
4
Path of a planet around the sun
5
Unit of energy
6
Infectious microscopic agent
8
Disturbance that transfers energy
9
Measure of matter in an object
12
Second lightest element
Down
2
Chemical element in table salt
3
Center of an atom or cell
7
Unit of force
10
Blocking of light by a celestial body
11
Substance with pH below 7