The importance of atmospheric differential refraction in spectrophotometry

Abstract

The effects of atmospheric differential refraction on astronomical measurements are much more important than is generally assumed. In particular, it is shown that relative line and continuum intensities in spectrophotometric work may be erroneous if this phenomenon is neglected. To help observers minimize these errors, the relation between object position and optimal slit or aperture orientation is derived, and practical tables and graphs are presented for use at the telescope.