Gravitation

2. First planet discovered with the use of a telescope.
5. It has no moons or rings.
6. Closest star system and planetary system to Earth's solar system.
8. The time a given astronomical object takes to complete one orbit around another object.
10. Largest planet in our solar system.
12. Shape of Earth's orbit around the sun.
15. Closest planet to the sun.
17. Reddish, terrestrial planet.
19. Object with an orbital period the same as the Earth's rotation period.
20. Speed needed by an object to break free of a planet or moon's gravity well and leave it without further propulsion.

1. Free fall acceleration of an object in a vacuum.
3. Property of the motion of a body traveling a circular path, directed radially toward the centre of the circle.
4. SI unit for distance.
7. Planet named after the Roman god of the sea.
9. A body intentionally placed in orbit around the earth or another planet.
11. SI unit for force.
13. SI unit for time.
14. Speed at which an object orbits a more massive central object.
16. It has more moons than any other planet.
18. First artificial satellite to orbit the Earth.