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Across 3. First photographic discovery of a minor planet 5. First astronomer to discover galaxies 6. Along with Penzies, discovered Cosmic Background Radiation 11. Discoverer of "Galilean" satellites of Jupiter 12. British astronomer, first to calculate a comet's orbit 13. Discovered Uranus in 1871 17. Discovered Pluto's moon Charon in 1978 18. Discovered the asteroid Juno in 1904 19. Formed the "Celestial Police" in 1800 21. Danish astronomer, helped make H-R diagram 22. Noted low sunspot activity from 1646 - 1718 23. First to identify the Doppler effect in astronomy

Down 1. Helped formulate the "Steady-State" theory in 1948 2. First observed Neptune in 1846 4. Discovered the dwarf planet Pluto 5. British Mathematician who discovered the sextant 7. Proved light does not travel through "ether" with Michelson 8. Predicted the existence of a planet beyond Neptune 9. Formulated Huygens Principle 10. French comet hunter best known for his 110 object list 14. Observed "canali" on Mars 15. Black astronomer, predicted eclipse in 1789 16. First discover Bode's Law in 1766 17. Formulated the heliocentric model of the solar system 20. Wrote "A brief History of Time"