1.
A game or problem that requires thought to solve.
2.
A tool used for navigation and orientation.
3.
Very old or from a long time ago.
4.
The line where the earth and sky appear to meet.
5.
A mathematical statement showing equality.
6.
All of space and everything in it.
7.
The force that pulls objects toward Earth.
8.
When one celestial body blocks another from view.
9.
An explanation of something based on evidence.
10.
A new idea, device, or method.
