Astronomical Photometry with CCDs:  
Turning a Small Telescope into a Large Telescope and the Large Telescopes do the Previously Impossible. 
A. G. Davis Phillip 
Union College.
Harlow Shapley Visiting Lecturer 
of the American Astronomical Society

      A little over a decade ago a new instrument arrived which has
revolutionized observational astronomy - the Charge-Coupled-Device.
A small chip of silicon acts as thousands of individual photometers
to take highly detailed pictures of areas on the celestial sphere.
Unlike the photographic plate, which has a distinctly non-linear response
to incoming photons, the CCD has a linear response over a range of
many magnitudes. In my work I have been able to do photometry on globular
clusters with a 1-meter telescope that would have taken a 4-meter
telescope previous to the CCD. Large telescopes are now able to construct
cluster color-magnitude diagrams of clusters and stars in external
galaxies. The Hubble Space Telescopes is taking pictures of galaxies
that formed soon after the Big Bang. In the talk I will start by describing
how a CCD works and then give examples of applications of the device to
astronomical projects.

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