Characterizing the Temporal and Spatial Stability of Atmospheric Transmission from 400 to 1050 nm.

The transmission function of the atmosphere is formally a function of wavelength, time, and line-of-sight. Making simplifying assumptions, such as linearity with airmass and temporal stability, enables the coarse removal of atmospheric extinction from ground-based observations of astronomical sources. However, these assumptions have not been rigorously justified to percent level precision, and small scale temporal or spatial variations could introduce non-negligible systematic errors. Systematic errors due to the atmosphere stand to inhibit the high precision measurements which are the focus of next-generation astronomical studies. We present a method of characterizing temporal and spatial variation in atmospheric transmission via spectrographic measurements of at least two standard stars simultaneously. These observations can be made on small-aperture telescopes with a simple spectrograph and can be coupled to large-aperture astronomical telescopes in order to provide real-time atmospheric diagnostics. We also present a spectrograph designed to yield efficient observations on the broad wavelength range of 400-1050 nm and our first results from this instrument.