Annu. Rev. Astron. Astrophys. 1991. 29: 89-127 Copyright © 1991 by Annual Reviews. All rights reserved

2.7 Cosmic Ultraviolet Background Radiation

In what follows we begin examining the available data, but before doing so consider again Figure 4, for comments on the true signal, rather than for the various sources of noise.

True diffuse ultraviolet background radiation is clearly present in the original of Figure 4, showing as broad, faint vertical bands in the wavelength range 2500 to 3200 Å, in the rightmost part of the figure. This is zodiacal light, and its brightness is of order 1500 units. At wavelengths shorter than 2500 Å, no signal is apparent. From this we can conclude that the true cosmic background is well below 1000 units shortward of 2500 Å. Analysis (81, 82) indicates that the average background on this target is 520 ± 200 units (1650-3100 Å Johns Hopkins UVX spectrometer) and 100 ± 200 units (1200-1700 Å spectrometer). Potential origins for this radiation are discussed below.