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T. A. Livengood, K. E. Fast (U. of MD, C.P. \& NASA/GSFC), Th. Kostiuk, F. Espenak, D. Buhl (NASA/GSFC), J. J. Goldstein, T. Hewagama, K. H. Ro (Challenger Ctr.)
Many infrared observations in solar system science require high spatial resolution and accurate registration of measurements at multiple wavelengths. Astronomical instruments operating at mid-infrared wavelengths (~5 - 20~\mum), which are very significant for solar system temperatures and molecular composition, generally are guided with a visible-light imaging system. Refraction in the earth's atmosphere may displace the visible and infrared images by up to several arcseconds depending on the zenith angle of the observation. In order to point accurately at the desired location on the source -- {\it e.g.}, the limb of Titan, a given hemisphere of Neptune, auroral regions on Jupiter - and register accurately multi-wavelength phenomena, it is necessary to account for the different atmospheric refraction between the guiding wavelength and the wavelength(s) of interest. This is particularly true for single-element detection systems.
We have measured the differential refraction between visible wavelengths and 12~\mum on four occasions and have found the refraction to differ significantly from the accepted dispersion used in astronomical calculations. The generally accepted formulation is based on data covering only the visible range and thus there is little reference for atmospheric refraction at infrared wavelengths. We will report on astronomical measurements of the differential refraction between the visible and 12~\mum regions and illustrate the application of refraction calculations to specific observations.
The author(s) of this abstract have provided an email address for comments about the abstract: timothy.a.livengood@gsfc.nasa.gov