1. Reflecting Telescopes

2. Mirrors A flat mirror reflects light in straight lines. A curved mirror can focus light to a point. A perfect parabolic mirror has a focal length like a lens. –All frequencies focused to the same point focal length focal point

3. Newtonian Reflector A primary mirror and eyepiece are combined. The telescope is cheaper, because a mirror is easier to make than a lens. primary mirror secondary diagonal mirror eyepiece

4. Schmidt-Cassegrain Reflector Cassegrain focus makes the tube up to three times longer. The extra mirror can distort the image. Schmidt corrector lens corrects for this distortion, called spherical aberration. eyepiece Schmidt corrector lens

5. Telescope Advantages REFRACTOR Superb resolution Good for detail Rugged alignment Transports well REFLECTOR Inexpensive optics Large aperture Good for dim objects Uniform treatment of colors SCHMIDT-CASSEGRAIN Portable size Combines best optical qualities Good for photography

6. Altazimuth Mount Telescope mounts should permit two directions of motion. Altazimuth mounts directly control altitude and azimuth. azimuth control altitude control

7. Equatorial Mount Altazimuth mounts do not track with the star’s movement. Equatorial mounts are oriented to the pole. Allows control of declination and right ascension. polar axis declination axis

8. Keck Reflector World’s largest reflector is in Hawaii. 400 inch aperture, f/1.75. Focal length is 57.4 feet. Telescope height is 81 feet. Keck Observatory