Across
1
Particle of light
4
Smallest unit of an element
7
Reddish electrical conductor
9
Measure of matter in an object
10
Icy body with a tail near the sun
11
Blocking of light by a celestial body
Down
2
Force that attracts objects together
3
Our home planet
5
Second lightest element
6
Biological catalyst
8
Path of a planet around the sun
12
The Red Planet