Subject

Astronomy & Cosmology

The universe at large scale — stars, galaxies, the cosmic microwave background and the expansion and origin of the cosmos.

2 papers in this field

AstronomyThe Astrophysical Journal · Jul 1965 Open access

A Measurement of Excess Antenna Temperature at 4080 Mc/s

A. A. Penzias and R. W. Wilson

Penzias and Wilson reported that the 20-foot horn-reflector antenna at Bell Telephone Laboratories in Holmdel, New Jersey, measured an excess zenith antenna temperature of about 3.5 K at 4080 Mc/s (4.08 GHz) that could not be attributed to known sources of noise. They found this excess radiation to be isotropic, unpolarized, and free of seasonal variation within their measurement limits. In a companion paper, Dicke and colleagues interpreted this signal as relic radiation from a hot early universe, and it is now recognized as the discovery of the cosmic microwave background, providing key observational support for the Big Bang model.

cosmic microwave background big bang radio astronomy blackbody radiation

AstronomyProceedings of the National Academy of Sciences · Mar 1929 Open access

A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae

Edwin Hubble

Hubble combined distances to roughly two dozen extra-galactic nebulae (galaxies), estimated largely from Cepheid variables and other stellar indicators, with their measured radial velocities to test for a systematic relationship. He found an approximately linear correlation in which the radial velocity of a nebula increases with its distance, with a proportionality constant of about 500 km/s per megaparsec. This velocity–distance relation, now known as Hubble's law, provided the first observational evidence that the universe is expanding and became a cornerstone of modern cosmology.

hubble's law expanding universe redshift extragalactic nebulae