16. 6-in Newtonian on a Dobsonian Mount “ 6-in” indicates that the telescope uses a 6-inch diameter mirror as its main light gathering optic This Orion Telescopes XT6 is an excellent scope for beginners and is reasonably priced
17. Compound Scopes: Schmidt-Cassegrain Cutaway view of an SCT Maksutovs are similar yet use a more curved front lens Main mirror Lens Meade Telescopes 8-inch SCT Eyepiece
30. Star Scintillation This montage of photographs shows how a single star’s image is distorted over time by atmospheric seeing or turbulence Ideal star image
31. Why do Star’s Twinkle? Turbulent air causes a star’s image to distort
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33. Effects of LP http://www.spaceweather.com/swpod2003/20aug03/Carlson1.jpg
34. Kitt Peak LP The view from Kitt Peak National Observatory of the Tuscon, Arizona skyline in 1959 The same skyline in 1972
35. US at Night http://archives.cnn.com/2000/US/08/24/dimming.the.lights.ap/large.usa.lights.jpg