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Across 3. two asteroids that revolve around each other and are held together by the gravity between them. Also called a binary asteroid. 6. the time of the year when the Sun appears furthest north or south of the celestial equator. 8. a large grouping of stars, from a few dozen to a hundred thousand, that are bound together by their mutual gravitational attraction. 9. an exploding meteorite. 11. any of the four outer, gaseous planets: Jupiter, Saturn, Uranus, and Neptune. 13. a system of two stars that revolve around a common center of gravity. 15. a star that flares up to several times its original brightness for some time before returning to its original state. 17. one thousand electron volts 18. a temporary disturbed area in the solar photosphere that few appears dark because it is cooler than the surrounding areas. 19. the total or partial blocking of one celestial body by another. 20. the two points at which the Sun crosses the celestial equator in its yearly path in the sky.

Down 1. angle in degrees above the horizon. 2. are hot, blue giants. They are extremely turbulent light and have a temperature of 50,000 °K and higher. 4. a phenomenon that occurs when the Earth passes into the shadow of the Moon. 5. a term used to describe matter in the universe that cannot be seen, but can be detected by its gravitational effects on other bodies. 7. the death explosion of a massive star, resulting in a sharpincrease in brightness followed by a gradual fading. 10. an extremely bright meteor. Also known as bolides, fireballs can be several times brighter than the full Moon. Some can even be accompanied by a sonic boom. 12. the highest energy (shortest wavelength) photons in the electromagnetic spectrum. Gamma rays areoften defined to begin at 10 keV, although radiation from around 10 keV to several hundred keV is also referred to as hard x-rays. 14. an instrument used to collect large amounts of from far away objects and increase their visibility to the naked eye. 16. a small particle of rock or dust that burns away in the Earth's atmosphere.