The Sun and the Solar System

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Across
  1. 2. a dark region on the sun's surface
  2. 5. fourth state of matter consisting of charged particles
  3. 9. model of the universe where Earth stood still in the middle
  4. 11. proposed the heliocentric model of the universe
  5. 12. a force of attraction between two objects with mass
  6. 14. eighteenth century nobleman and astronomer
  7. 15. center of the sun
  8. 17. the sun's thin outer atmosphere
  9. 18. polar displays of colour and light
Down
  1. 1. combining nuclei of lighter elements to form heavier elements
  2. 2. constant stream of electrically charged particles given off by the corona
  3. 3. invented calculus
  4. 4. sun centered model of the solar system
  5. 6. largest planet in the solar system
  6. 7. discovered that planet orbits were elliptical
  7. 8. closest planet to the sun
  8. 10. negatively charged particle found in an atom
  9. 13. apparent backward motion
  10. 16. positively charged particle located in the nucleus