Virginia Trimble1,2
Abstract. The significance of the cosmic
microwave background or CMB (3K, ther-
mal, relict, black body, isotropic, etc) radiation in confirming a hot
big bang model
of the early Universe and in setting precise values of many of the
parameters of that
model is widely known and has recently been enhanced by the results of
three years of
operation of the Wilkinson Microwave Anisotropy Probe (WMAP). There are,
however, also backgrounds of astrophysical and cosmological significance
consisting of
photons of other wavelengths, other forms of radiation, particles, and
fields. Several
predate the discovery of the CMB, while others are relatively recent
discoveries. This
article explores the history of their predictions and discoveries and
their cosmological
and astrophysical implications as currently understood.
Keywords: cosmic rays magnetic
fields - gravitational waves - neutrinos - gamma-
rays: observations -X-rays: diffuse background - ultraviolet: general -
infrared: general - radio continuum: general
1Department of Physics and
Astronomy,University of California, Irvine CA 92697-4575, USA
2Las Cumbres Observatory, Goleta,
California