Across
- 4. Exist between stars and are made up of hydrogen and helium gases
- 8. The first idea for the model of the solar system
- 9. The fourth planet from the Sun
- 12. The apparent backward movement of a planet
- 14. The first planet to form in the solar system
- 15. Who discovered the idea of a heliocentric solar system model
- 18. Left over particles from the formation of the solar system
Down
- 1. First to use a telescope to observe the sky
- 2. The current idea for the model of the solar system
- 3. Material remaining from the formation of planets
- 5. A hard and rocky planetesimal (found in the asteroid belt)
- 6. What happens to a interstellar cloud when it becomes to dense
- 7. Discovered three laws of planetary motion
- 10. A bright ball of gas
- 11. A cold and icy planetesimal (found in the Oort Cloud)
- 13. The moon that has frozen seafloor volcanoes
- 16. Discovered the law of gravity
- 17. The shape a interstellar cloud takes when it collapses fully
- 19. The measurement of distance that is equal to the distance from the Earth to the Sun
- 20. The largest star in our solar system