Across
1
Path of a planet around the sun
4
Center of an atom or cell
5
Nerve cell in the brain
7
Molten rock beneath Earth surface
10
Second lightest element
12
Glass that splits light into spectrum
Down
2
Chemical element in table salt
3
Force that attracts objects together
6
Compound containing oxygen
8
Blocking of light by a celestial body
9
Gas essential for breathing
11
Biological catalyst