Houston, TX, Feb. 1979) has analyzed the situation and concludes that each antenna's reflected spot will illuminate any given observer on approximately two successive nights in the spring and two in the summer. The period of illumination can be as long as 2 minutes and, as mentioned above, will be significantly brighter than the full moon. It should be noted that this illumination comes from a much smaller object and corresponds to a much larger surface brightness than that of the moon. The surface brightness is expected to be just the reflectivity of the satellite times the surface brightness of the Sun. High-surface brightnesses are of special concern regarding possible local damage to the photosensitive surface of any imaging optical detector that can resolve or nearly resolve the satellite. As one example, the dark-adapted human eye may be at risk. C. DIFFUSE SKY BRIGHTNESS Increases in diffuse sky brightness are expected from either the diffuse reflection from the solar collector or the specular reflection from the antenna. The effects of these two phenomena are quite different. The diffuse reflection is a persistent effect. The satellites always occupy the same position in the sky, with their apparent brightness varying with time as described in the appendix. The apparent positions of the individual satellites, for a 60-satellite system, as seen from Kitt Peak, Cerro Tololo, and Mauna Kea are shown in Figure 1. The net effect of the diffuse brightness of these satellites can be estimated using Ivan King's study of the profile of stellar images (Publi- cations of the Astronomical Society of the Pacific, Volume 83, p. 199, 1971). 2 He found that well away from a star the sky brightness falls off as r , such that the sky brightness around an object, in magnitudes per square second of arc, is given by where m(obj) is the apparent visual magnitude of a satellite's solar blanket, and r is the angular separation in arc seconds. The total contribution of the Reference System to diffuse sky brightness is, therefore, simply the superposition of the effects of the 60 satellites.
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