The members of the working group were: B. Balick P. Boyce K. Clark J. Gallagher E. Groth D. Harper G. Stokes, Chairman THE NATURE OF ASTRONOMICAL OBSERVATIONS Counting Photons The actual method of conducting astronomical research is the root of any effect of the proposed SPS on astronomy, and on optical astronomy in particular. Astronomy is an observational rather than an experimental science. Although laboratory measurements of the properties of matter are extremely important to astronomy, the success of astronomical research is measured largely by its ability to explain objects and phenomena over which we have no control. Astronomy is the extreme case of remote sensing. The information we have about astronomical objects comes almost entirely from our ability to detect the electromagnetic radiation emitted, reflected or affected by the astronomical objects. As noted in the introduction to these proceedings, astronomy is sometimes divided according to the portion of the electromagnetic spectrum under study. An important characteristic of optical astronomy is its preoccupation with the detection of photons. A photon can be thought of as a packet of light. A photon of visible -12 ---- light represents about 4 x 10 ergs of energy, which means that if a 100-watt on light bulb emitted 100 watts of visible photons, it would emit 10 of them every second. Detectors used in optical astronomy are sensitive enough to detect single photons. In many cases, astronomical detectors are merely photon counters.
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