Solve these clues to fill the grid.
- A collection of star systems
- 5 Across
- How much matter something contains
- 6 Across
- The tendency of a body to maintain its state of rest or uniform motion unless acted upon by
- 9 Across
- Distance travelled per unit time
- 10 Across
- Any collection of particles or gases that is visible (plural)
- 11 Across
- Everything that exists anywhere
- 12 Across
- How hot or cold something is
- 13 Across
- How tightly packed the matter in something is
- 14 Across
- How loud something is, or how much space it fills
- 15 Across
- Force that pulls objects toward the Earth
- 1 Down
- Any celestial body orbiting around a planet or star
- 2 Down
- The path described by one celestial body in its revolution about another
- 3 Down
- The length of a line segment between the center and circumference of a circle or sphere
- 4 Down
- The property of relative size or extent
- 7 Down
- Natural satellite that orbits the Earth
- 8 Down