Telescopes
• Many different telescopes for different applications
– Wavelength specific
– Detail specific
• Common telescopes are designed for visual light
• Eye glasses for far­sighted people developed in 13th century, a couple centuries later the telescope was developed from this technology
• Galileo was the first to use a telescope for astronomy
Telescopes
• Galileo used a refracting telescope (~1608)
• The telescope consisted of glass lens
• A plano­convex lens focuses the light onto a focal point
• An eyepiece (plano­concave) is then used to magnify and view the object
• Improved the refracting telescope using his knowledge of mathematics
Telescopes
• Refracting telescopes not perfect
– Distortion on the edges
– Magnification is inversely proportional to field of view
– Chromatic aberration
• Solutions
– Use convex lens instead of concave (Kepler ­­ using mathematics)
– Use mirror instead of lens
Telescopes
• Newton invented the reflecting telescope
• Initially very hard to make appropriate mirrors, hence this did not become popular until the 1800s
Telescopes
• Reflectors had problems as well
– Different aberrations
• Coma
• Spherical aberrations for non­
parabolic mirrors
– Central obstruction
– Refractors have slightly brighter objects given the aperture size
– Sensitive to collimation
• Today reflector telescopes are considerably cheaper than refractor telescopes
Telescopes
• There are a number of different types of reflecting telescopes, each resolving one or two issues however leaving other issues unresolved
• Application determines which to use (or not to use)
Reflecting telescopes
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Newtonian
Cassegrain
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Ritchey­Chrétien
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Hubble –
Specialized Cassegrain
Schmidt­Cassegrain
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Very short, compact, and cheap
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Favorite of amateurs (Celestron)
Maksutov­Cassegrain
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Concave Mirror
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Earth observing
Dall­Kirkham
Herschelian
Off­axis telescope (therefore no central obstruction)
Schiefspiegler
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Better resolution than schmidt­cassegrain, however heavier
Nasmyth
Gregorian
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Compact
Off­axis telescope (Cassegrain variant)
Yolo –
Off­axis telescope
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Toroidal reflectors
Reflecting Telescopes
• Liquid!
• Mercury!
• Rotating to form a perfect paraboloid
• Issac Newton’s idea
– Ahead of his time
• http://www.astro.ubc.ca/LMT
• Other liquids might be useful on the moon to make HUGE telescopes!