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Across 3. The apparent change in frequency and wavelength of energy radiated by a source as a result of the motion of the source or the observer D 6. A model of the universe that places the sun at the center of the solar system 9. he name generally applied to the day of the year with the shortest period of sunlight 10. A piece of rock that moves through space 12. A measure of the elongation of an ellipse 14. The theory that the universe formed as a concentration of matter expanded explosively bioclastic sedimentary rocks: Rocks com posed of materials made from or by living organisms 15. The process by which the nuclei of light elements, such as hydrogen, under intense heat and pressure form the nuclei of heavier elements, such as helium 17. An object in space that revolves around another object as a result of gravity 21. an annual astronomical phenomenon that brings the longest day of the year and the first day of summer in the Northern Hemisphere 22. The total energy output of a star; absolute brightness 23. the distance between identical points (adjacent crests) in the adjacent cycles of a waveform signal propagated in space or along a wire. 25. A model of the universe that assumed that Earth is stationary and at the center of the universe 26. move around an object 27. The height at which rising air begins to form clouds 28. The force of attraction between all objects 29. the act of rotating on an axis 30. a displacement in the spectral lines

Down 1. A closed curve formed around two fixed points such that the total distance from any point on the curve to both fixed points is constant 2. a rocky planet whose composition is similar to earths 4. The point in the sky directly over an observer's head 5. A streak of light produced as a meteoroid burns due to friction with Earth's atmosphere 7. a meteoroid that strikes earths surface 8. A planet whose composition is similar to Jupiter's; also know as a gas giant 11. a fixed luminous point in the night sky 13. A short-term darkening of the moon caused by the moon orbiting through Earth's shadow 16. A huge group of stars held together by gravity 18. One of the two days each year on which the sun rises due east and sets due west, on which the length of day and night are equal, on which the sun's vertical rays are at the equator; the first day of spring or fall 19. An object made of ice and rock fragments that revolves around the sun usually in a highly eccentric orbit; it may be visible periodically in the night sky as a small spot of light with a long tail 20. The distance electromagnetic energy can travel in 1 year, approximately 6 trillion mi (10 trillion km) 21. A short-term darkening of the sun caused by the moon passing in its orbit between Earth and the sun 24. An irregularly shaped rocky mass that is smaller than a planet and occupies an orbit around the sun; most are found between the orbits of Mars and Jupiter