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Across 1. The core of a super massive star that remains after a supernova, leaving a point of zero volume, but infinite density - exerts a tremendous gravitational pull that nothing can escape. (2 Words) 8. The distance that light can travel in one year in through space, which is about 5.8 trillion miles or 9.5 trillion kilometers. 9. The hottest stars, with temperatures up to 50,000 degrees Celsius. (2 Words) 12. Stars that have exhausted their hydrogen fuel and are burning helium and heavier elements. (2 Words) 13. The smallest stars, which are usually about 15–20 km in diameter. (2 Words) 14. The stable “middle age” of a star, when it has sufficient fuel for nuclear fusion of hydrogen to occur. (3 Words) 17. The coolest stars, with an average temperature of 3,000 degrees Celsius. (2 Words) 19. The brilliant explosion of a huge star that has reached the end of its lifetime. 22. All of the planets, stars and celestial bodies that are part of the spiral galaxy to which our solar system belongs. (2 Words) 23. A cloud of gas and dust in space; nebulae are believed to be the origin of stars and our solar system.

Down 1. Two stars that circle around each other. (3 Words) 2. A gaseous substance that is the smallest and lightest of all chemical elements and is the most abundant element in the universe; the primary fuel for most stars, including our sun. 3. The collapse of a medium-size star, like our sun, into a very small, very hot dense body smaller than the Earth; occurs after the red giant phase. (2 Words) 4. The largest stars. They can be 1,000 times larger in diameter than our sun. 5. The third hottest category of stars. (2 Words) 6. The second hottest category of stars. (2 Words) 7. Except for our sun, the closest star to the Earth, located 4.2 light-years away. (2 Words) 10. A chemical reaction in which atomic nuclei combine to form a heavier element, releasing huge amounts of energy during the process. (2 Words) 11. A group of stars that form a recognizable pattern or outline in the sky, which many ancient civilizations associated with myths and legends. 15. Also known as the Dog Star; a binary star system that contains the brightest star we can see from the Earth. 16. A gaseous substance that is the lightest element next to hydrogen and makes up 23 percent of the mass of the universe; produced through nuclear fusion of hydrogen in the core of stars like our sun. 18. A body of glowing gases in space that shines due to the energy produced in its core from nuclear fusion reactions. 20. The temporary, extreme and unexpected brightening of a star, caused by an exploding star 21. A group of hundreds of millions of stars, dust, gas and other objects that is held together in space by gravity.