Across
1
Reddish electrical conductor
3
Amplified beam of light
7
Smallest unit of an element
8
Path of a planet around the sun
9
Infectious microscopic agent
11
Form of thermal energy
13
Positive particle in nucleus
Down
2
Ball of burning gas in space
4
Unit of force
5
Unit of heredity
6
Blocking of light by a celestial body
10
Unit of energy
12
Mass per unit volume