Extragalactic Background Light: Measurements and Applications
  This review covers the measurements related to the extragalactic background
light (EBL) intensity from gamma-rays to radio in the electromagnetic spectrum
over 20 decades in the wavelength. The cosmic microwave background (CMB)
remains the best measured spectrum with an accuracy better than 1%. The
measurements related to the cosmic optical background (COB), centered at 1
microns, are impacted by the large zodiacal light associated with
interplanetary dust in the inner Solar system. The best measurements of COB
come from an indirect technique involving Gamma-ray spectra of bright blazars
with an absorption feature resulting from pair-production off of COB photons.
The cosmic infrared background (CIB) peaking at around 100 microns established
an energetically important background with an intensity comparable to the
optical background. This discovery paved the path for large aperture
far-infrared and sub-millimeter observations resulting in the discovery of
dusty, starbursting galaxies. Their role in galaxy formation and evolution
remains an active area of research in modern-day astrophysics. The extreme UV
background remains mostly unexplored and will be a challenge to measure due to
the high Galactic background and absorption of extragalactic photons by the
intergalactic medium at these EUV/soft X-ray energies. We also summarize our
understanding of the spatial anisotropies and angular power spectra of
intensity fluctuations. We motivate a precise direct measurement of the COB
between 0.1 to 5 microns using a small aperture telescope observing either from
the outer Solar system, at distances of 5 AU or more, or out of the ecliptic
plane. Other future applications include improving our understanding of the
background at TeV energies and spectral distortions of CMB and CIB.
