Across
1
Blocking of light by a celestial body
5
Smallest unit of an element
6
Mass per unit volume
7
Chemical element in table salt
8
Biological catalyst
Down
2
Gas essential for breathing
3
Second lightest element
4
Absolute temperature scale unit
9
Compound containing oxygen
10
Icy body with a tail near the sun
11
Center of an atom or cell
12
Ball of burning gas in space