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Across 2. Technique of connecting multiple telescopes to act as a single large telescope. 4. We experience seasons on Earth because Earth's rotational axis is ______ with respect to its orbital axis. 6. The altitude (angle above the horizon) of the north celestial pole equals the observer's ________. 9. It is dangerous to ride in a car without a seatbelt due to Newton's _____ law. 11. According to Kepler's third law, a planet's orbital ______ squared is proportional to the semi-major axis of its orbit cubed. 13. The ________________ divides the sky into northern and southern halves. (2 Words) 14. Earth's atmosphere is completely transparent to visible light and this type of radiation. 18. The phase of the moon after first quarter is ______ gibbous. 19. Ptolemy modified the geocentric model of the universe using epicycles to account for this. (2 Words) 20. The gravitational force between two bodies _________ as the distance between them increases. 21. Stars that are close enough to the celestial poles that they never rise or set. 23. Apparent motion of an object because of the motion of the observer. 24. A permitted orbit of an electron in an atom is also known as a(n) _____________. (2 Words) 26. If x-ray radiation hits a mirror head-on, it will pass right through due to its _____ wavelength. 27. The type of radiation with the highest energy. 28. The __________ of Earth around the sun produces the cycle of the year. 30. During a solar eclipse, the moon is in this phase. 33. The distance between two crests or troughs of a wave. 34. Copernicus devised this model of the universe which places the sun at its center. 37. Apparent path of the sun on the sky. 38. The ________ of Earth on its axis produces the cycle of day and night. 40. Atoms prefer to be in this energy state. 42. According to Kepler's second law, a planet moves ______ when it is closer to the Sun in its orbit. 43. __________ telescopes use a lens. 44. The intersection of the sun's path with the celestial equator. 46. Two or more atoms bound together. 47. A packet of light is called a ______. 48. The tilt of the moon's orbital plane with respect to the ecliptic can result in a(n) _______ solar eclipse.

Down 1. Electronic device that records images. 3. For every action there is a(n) _______________ reaction. (3 Words) 5. An element with a different number of neutrons than protons. 7. The average distance between the sun and Earth. (2 Words) 8. The size of a telescope's main mirror/lens is called its ________. 10. The atmospheric effect that causes stars to twinkle is __________. 12. During a total lunar eclipse, the moon looks ___ because sunlight is refracted through Earth's atmosphere. 15. Astronomers divide the sky into 88 of these. 16. The number of peaks or troughs of a wave that pass per second. 17. If the moon fully enters the _____ of Earth's shadow, the lunar eclipse is total. 22. An atom can become excited through collision with an electron or __________ of a photon. 25. _________ telescopes use a mirror. 29. An atom with a different number of electrons than protons is called a(n) ___. 31. When an electron moves to a higher energy level in an atom, the atom is said to be _______. 32. Aristotle devised this model of the universe which places Earth at its center. 35. Stars south of the celestial equator are up for more than twelve hours for an observer in the ________ hemisphere. 36. An excited atom will go from a higher energy state to a lower energy state and ____ a photon. 37. According to Kepler's first law, planets follow ________ with the sun at one focus. 39. Transparency of the atmosphere to different types of radiation. 41. A solar eclipse occurring when the moon is farthest from Earth is a(n) _______ solar eclipse. 45. The atmosphere is completely opaque to gamma rays and this type of radiation. 46. According to Newton's second law, force is proportional to this times acceleration.