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Young's Photo Gallery

James W. Young, Professional Photographer

Image of the Week Archives

  April 26, 2015
  I have decided to be different this week!  What is this, you ask?  This is a very
 out-of-focus image of the star Vega taken with the 24-inch telescope at JPL's
 Table Mountain Observatory on October 31, 2007.  This particular image was
  used to confirm the final mirror alignment of the telescope after the primary
  mirror was removed for cleaning and re-coating of aluminum, then re-installed.
  The dark circle in the center is the obscuration of the secondary (smaller) mirror
    that reflects the starlight down to the camera at the base of the telescope tube. 
    Carefully note the small faint dot of light in the very center of the dark circle. 
   If the alignment of the optical mirrors was not perfct, this dot would not appear
  in the center.

  The four symetrically placed dark lines from the center circle to the outside larger
 circle edge, are the refraction patterns of the four thin metal 'vanes' that hold
 the secondary mirror and housing.  The one at the bottom is darker (and wider)
 because it has an additional thin wire cable to supply the necessary voltage to
 control the motion of the mirror (in and out of focus).

Any question?  Write to me here:  astroyoung@verizon.net

 The alignment of a telescope's optical system is one of the most critical factors
in making accurate astronomical observations.

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e-mail astroyoung@verizon.net

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