Weak band emissions from minor atmospheric components would find obvious competition from scattering. The numerical estimates of limits cannot well be reckoned because of the variable stringencies of different experimental tasks, the ranges of thin haze cover, and the various contributions from aerosol and Rayleigh scattering. Effects would translate into reduced hours and poor intensity discrimination. Actual examples are probably the best evidence. Moonlight now limits the validity of ground-based spectrophotometric measurements. Typically, a quarter moon sets the limit on photometry anywhere in the clear sky, and for many studies the moon cannot be present in any phase of its brightness. The emission by incident hydrogen, regardless of its Doppler profile, is an important observational link in magnetospheric interaction studies; the blue H-beta line is the best to use, and narrow interference filters are variously employed for it. The villainy of scattered moonlight is heightened by the structure of Fraunhofer absorption lines in the solar spectrum near H$; spurious results can come from scanning the filter pass band because of the contaminating scattered light from the sky. The moon must be gone. The moon would never be gone, at any hour or any day, if the satellites contributed the equivalent of a 1/8 crescent. The background solar spectrum scattered in the dark hours would effectively end many desired aeronomic studies based on faint airglow and aurora. REFERENCES Perkins, F. W. and R. G. Robie, Journal of Geophysical Research. 83(A4): 1611-1624, 1978. Holway, L. H., Jr. and G. Meltz, Journal of Geophysical Research. 78(A34): 8402-8408, 1973.
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