The High-Latitude Sky at IR, Optical, and UV Wavelengths

Abstract

We review the current data on the not-so-dark sky covering infrared, visible and ultraviolet wavelengths. Here, we are mainly concerned with the emission from the interstellar gas and dust above and below the galactic plane. Zodiacal light is not discussed in detail and emission from unresolved stars is briefly mentioned. Recent improvements in these studies have been made with the use of new satellite UV data, the use of high-performance CCD in the visible spectrum and extensive analyses from the Infrared Astronomical Satellite (IRAS). We show that cirrus clouds which subtend a large solid angle at high galactic latitudes are made of neutral gas and dust, are within a few hundred parsecs of the Sun, and are almost optically thin up to UV wavelengths. The brightness of these clouds, expressed as vIν = λIλ, is estimated to be within 10–8 and 10–7 W m–2 sr–1 at almost all wavelengths from λ = 0.1 to 300 μm and peaks at 150 μm, for a typical column density of 3 × 1020 H cm–2. They may yield the fundamental limitation to all extragalactic and halo studies.