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November 3.docx

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Wilfrid Laurier University
Shohini Ghose

November 3, 2011 Telescopes:  A type of light collecting device  Light rays can be reflected (bounced off) or refracted (bent) at an interface between two materials Lens:  A lens has usually two refracting surfaces  If the surfaces are close, we have a thin lens  Refraction can cause parallel light rays to converge to a focus  The focal plane is where light from different directions comes into focus  The image behind a single (convex) lens is actually upside down. Your brain flips the image Basic designs of telescopes:  Refracting telescope: focuses light with lens (Galileo) o Need to be very long, to maximize the distance between the lenses o They have large, heavy lenses for good light collection  Reflecting telescope: focuses light with mirrors (Newton) o Reflecting telescopes can have much greater diameters o Modern telescopes (built after 1900) are reflectors What are the advantages of a reflecting telescope over a refracting telescope?  Only the reflecting surface of mirrors in a reflecting telescope have to be perfectly shaped. In a lens the entire shape of the lends and both surfaces are important  Objective lenses are heavy and difficult to stabilize at the top of the telescope. Heavy mirrors at the bottom of the telescope are less problematic  Small telescopes can use other focal arrangements that would be difficult in larger telescopes  Lenses have chromatic aberrations that must be corrected Two most important important properties of a telescope:  Light collecting area: Telescopes with a larger collecting area can gather a greater amount of light in a shorter time  Angular resolution: Telescopes that are larger are capable of taking images with greater detail Angular Resolution:  The minimum angular separatio
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