Across
- 3. A pure substance consisting of only one type of atom
- 5. The total energy a star emits per unit of time
- 6. A neutral particle in the nucleus of an atom
- 8. A luminous ball of gas undergoing nuclear fusion
- 15. An object, natural or artificial, that orbits another body in space
- 17. A scientist known for his laws of planetary motion
- 20. A positively charged particle found in the nucleus of an atom
- 21. The process where atomic nuclei combine, releasing energy
- 22. The scientific explanation for the origin of the universe
- 23. The smallest unit of an element that retains its properties
Down
- 1. The most abundant element in the universe, symbolized as H
- 2. A late stage in the evolution of a star when it expands and cools
- 4. The totality of all space, time, matter, and energy
- 7. The emission of energy as electromagnetic waves or particles
- 9. A star and all the objects bound to it by gravity, including planets
- 10. A natural event or fact that is observed to occur
- 11. A natural satellite orbiting a planet
- 12. The measure of the amount of matter in an object
- 13. A powerful explosion of a star, releasing tremendous energy
- 14. The branch of astronomy dealing with the physical properties of celestial bodies
- 16. A vast system of stars, gas, and dust held together by gravity
- 18. The curved path of a celestial object around a star or planet
- 19. A celestial body orbiting a star, massive enough to be rounded by its gravity