Space Systems

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