To Infinity and Beyond

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Across
  1. 2. Large grouping of stars, planets, and dust
  2. 4. Element containing one proton and one electron
  3. 10. Brightness of a star
  4. 14. Primary substance that makes up matter
  5. 15. Explosion of a massive star
  6. 16. A self luminous celestial body consisting of a mass of gas
  7. 17. Point of an orbit where the celestial body is farthest from the sun
Down
  1. 1. Unit of length equal to the distance that light travels
  2. 3. Theory that states the universe began as a small point that expanded
  3. 4. The lightest noble gas
  4. 5. point in the ellipse that help determines the shape
  5. 6. Curved path followed by a satellite as it revolves an object in space
  6. 7. Following the path of an ellipse
  7. 8. Range of light waves emitted by a celestial body
  8. 9. Point closest to the sun in the orbit of a celestial body
  9. 11. All space and the matter space contains
  10. 12. Device that measures different wavelengths of electromagnetic radiation
  11. 13. Distribution of energy in wavelengths in a system