if it is possible to make a marked reduction in their apparent luminosity, then the parallactic effect between the northern and southern hemisphere observatories would allow astronomical observations to be planned in a fashion that would minimize but not remove the effect of the SPS on observing programs. An object in LEO is not geostationary, and as it travels in its orbit around the Earth, the object will appear to move across the sky. Therefore, if the LEO structures are large and reflective, they would appear as bright planet-like objects moving relatively rapidly across the sky. Members of the working group pointed out that observations made with the 48-in. Schmidt telescope located on Mt. Palomar are routinely affected by existing satellites. The photographs made with this telescope cover a relatively large area of the sky, about the size of the bowl of the Big Dipper, and are usually made with exposure times of about one hour. Since there are a large number of objects now in orbit around the Earth, it is not unusual for a picture taken with this telescope to show the trails of satellites. Because current satellites are small, they are not very bright and the trails are primarily a nuisance. As LEO satellites get larger and brighter, it will be necessary to schedule observations to avoid them. IMPACT THRESHOLDS OF THE SPS ON OPTICAL ASTRONOMY Selecting the Thresholds for Adverse Effects Because there are natural sources of diffuse sky brightness (sunlight reflected by dust in the solar system and auroral and airglow in the Earth’s upper atmosphere), any effect of the SPS should be compared to those sources of radiation. Equation (1) provides the comparison through the parameter p, which is the factor by which the flux of radiation from the night sky is increased over its natural value. In general, the working group felt uncomfortable associating particular values of p with specific effects on optical astronomy. However, in the following paragraphs we suggest that p>l.1 results in a noticeable effect, that 1.3<p<2.0 creates a serious hindrance to optical astronomy, and that regions of the sky with p>2 are contaminated zones within which faint object astronomy is no longer a reasonable endeavor.
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