Reflecting Telescopes Mirrors A flat mirror reflects light

Reflecting Telescopes

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

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

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

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

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

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. declination axis polar axis

Keck Reflector • • One of the largest reflectors is in Hawaii. 400 inch aperture, f/1. 75. Focal length is 57. 4 feet. Telescope height is 81 feet. Keck Observatory