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Homework Help: Telescope Optics

  1. May 1, 2010 #1
    1. The problem statement, all variables and given/known data
    This is a question on my final review.

    Imagine you are given the task of designing the telescope in a spy satellite that is
    going to be launched into an orbit 500 km above the surface of the Earth. The agency you
    are working for wants to be able to clearly see objects as small as 1 inch = 2.5 cm (for
    example the headlines on a newspaper).

    a.) Calculate the angular resolution needed to achieve this.

    b.) Given that diffraction is the ultimate limitation of your telescope, how big will the
    primary mirror need to be? Use 500 nm for the wavelength of the light.

    c) In one or two sentences, comment on the feasibility of your design. Hint: for
    comparison the largest Earth based telescope has a 10 meter diameter mirror, the Hubble
    space telescope has a 2.4 meter diameter mirror.


    I am really lost.. My knowledge is very poor for this chapter, I read the chapter earlier and still don't know.

    Much help from your bright minds would be appreciated!!

    2. Relevant equations

    Not sure
    3. The attempt at a solution
    a. )
    Theta = Object height / Object Distance
    In that case it is 5.0x10^-8 degrees
    b.) How big will the mirror have to be..
    I used rayleigh's criterion.
    Theta(min) = 1.22(wavelength) / D
    Solved for D, giving 12.2m
    c.) No idea
  2. jcsd
  3. May 2, 2010 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    (a) Okay, but that should be in radians.
    (b) Looks good.
    (c) Mainly a common-sense question. How feasible is it to launch a telescope 5x larger (and 25x times the area) of Hubble? Or to not only build something larger than any telescope that has ever been built, ever, but launch it into orbit as well?
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