AKP: ASTRONOMY DAY - Keep looking up!

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Across
  1. 3. an eye in the sky
  2. 4. when only one star is seen
  3. 5. created at the end of a massive star
  4. 10. comets’ home
  5. 11. distance between two crests or troughs
  6. 12. planet where only robots roam
  7. 14. goes around what goes around
  8. 18. the densest planet
  9. 20. tool for two eyes
  10. 23. a mechanical model of a solar system
  11. 24. fireworks at the end of star life
  12. 26. a star astronomer
  13. 27. it contains big spoon
  14. 28. planet without any moons
  15. 29. path of a planet
  16. 31. a natural alchemy
  17. 35. related to moon
  18. 36. those 12 signs
  19. 37. star nursery or a graveyard
  20. 41. the beginning
  21. 43. Sun rises in the west here
  22. 44. wanderer of the sky
  23. 45. planet that goes sideways
  24. 46. the hunter
  25. 47. Rontgen ray
  26. 49. a ball of hydrogen and helium
  27. 50. it does not contain any matter
  28. 53. everything ever
  29. 54. a colorful display in sky
Down
  1. 1. a cold ice giant
  2. 2. milky way
  3. 5. a star astronomer
  4. 6. 3/21 or 9/21 would be equally good clues
  5. 7. a star astronomer
  6. 8. brings the sky down to earth
  7. 9. an infrared space observatory
  8. 13. a star astronomer
  9. 15. our sun is one (think Snow White)
  10. 16. a small rock in space
  11. 17. Galilean moons orbit this planet
  12. 19. connecting the starry dots
  13. 21. a big rock in space
  14. 22. this is where Cassini explored and took its final plunge
  15. 24. longest day or night
  16. 25. a spherical cloud outside solar system
  17. 30. an icy thing that moves in a long ellipse
  18. 32. star gazer
  19. 33. one lap of the planet
  20. 34. space between stars
  21. 38. an active galaxy near the supermassive blackhole
  22. 39. between half and full
  23. 40. astronomer’s tool
  24. 42. a star cluster
  25. 48. a cosmic hide and seek
  26. 51. original Planet 9
  27. 52. how many in a second?