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Across 1. remant stellar cores that have cast off their outer gas layers 5. groups of stars that have a similar characteristic emission lines 6. small, dense, round cloud of dust and gas that absorbs and appear as a black blob 7. formed when a massive star collaspes from its own gravity 10. the brightness of a star as seen from Earth 12. the phase of a star when the fuel begins to exhaust and the star expands its normal size 13. to determine electronis structure and gas 15. colorless, highly flammable gasesous element; the lightest of all gases and the most abundant element in the universe 17. nebula in which star formation is occuring 21. star that never becamse massive enough to start core hydrogen burning 22. having the component parts closely compacted together 23. star that has not yet started core hydrogen burning 24. large cloud of gas and dust in interstellar space; a region in space where stars are born. 25. to throw or give off light or heat

Down 2. brightness that a star would have at a distance of 32.6 light years from Earth 3. used to seperate a star's light into a spectrum 4. process by which multiple atomic particles join together to form a heavier nucleus 8. external force required to make a body followed a curved path 9. star in its final stages after it has used its energy supplies as a white dwarf 11. forace of attraction between objects that is due to their masses 14. graph that shows the relationships between a star's surface temperature and absolute magnitude 16. the total amount of a light that an object radiates lunar eclipse 18. the band of olors produced when white light passes through a prism 19. gigantic explosion in which a massive star collaspes and throw its outer layers into space 20. the act of blinking