Cosmic noise
Radio-frequency radiation from celestial sources beyond Earth's atmosphere.
Cosmic noise—also called galactic radio noise—is radio-frequency electromagnetic radiation that originates beyond Earth’s atmosphere. Its behavior is similar to that of thermal noise. This type of noise becomes detectable at frequencies above roughly 15 MHz when highly directional antennas are aimed at the Sun or at specific parts of the sky, such as the center of the Milky Way. Distant objects like quasars, which are extremely dense, emit radiation across the entire electromagnetic spectrum, including radio waves. The descent of a meteorite can also be picked up by a radio receiver: as the object burns up due to friction with the atmosphere, it ionizes surrounding gases and generates radio waves. Another form of cosmic noise is the cosmic microwave background radiation (CMBR), which is believed to be a leftover from the Big Bang. This radiation fills space almost uniformly across the entire sky, and while its bandwidth is broad, its peak intensity lies in the microwave range.
The first detection of radio waves from the Milky Way was made by American physicist and radio engineer Karl Jansky in August 1931. Working at Bell Telephone Laboratories in 1932, Jansky built an antenna designed to receive radio waves at 20.5 MHz (a wavelength of about 14.6 meters). After recording signals for several months, he sorted them into three categories: nearby thunderstorms, distant thunderstorms, and a faint, steady hiss of unknown origin. The location of the strongest signal rose and fell once a day, leading Jansky to initially think he was detecting radiation from the Sun. However, after several more months, he noticed that the brightest point drifted away from the Sun and that the pattern repeated every 23 hours and 56 minutes. He then concluded that the radiation came from the Milky Way and was strongest toward the galaxy’s center. Jansky’s work helped distinguish between the optical sky (what the human eye sees) and the radio sky, which includes daytime meteors, solar bursts, quasars, and gravitational waves.
Later, in 1963, American physicist and radio astronomer Arno Allan Penzias (born April 26, 1933) discovered the cosmic microwave background radiation. This discovery helped establish the Big Bang theory. Penzias and his colleague Robert Woodrow Wilson had been developing ultra-sensitive cryogenic microwave receivers for radio astronomy. In 1964, after building t
- discovery_of_galactic_radio_waves
- Karl Jansky, August 1931
- discovery_of_CMBR
- Arno Allan Penzias, 1963
- frequency_of_Jansky's_antenna
- 20.5 MHz
- wavelength_of_Jansky's_antenna
- approximately 14.6 meters
- Nobel_Prize
- Penzias and Wilson, 1978
- ARCADE_altitude
- over 35 km (21 miles)
Lore & Background
Karl Jansky, an American physicist and radio engineer, first discovered radio waves from the Milky Way in August 1931. At Bell Telephone Laboratories in 1932, he built an antenna designed to receive radio waves at 20.5 MHz. After months of recording, he categorized signals into nearby thunderstorms, distant thunderstorms, and a faint steady hiss of unknown origin. He initially thought the maximum intensity came from the Sun, but later found the cycle repeated every 23 hours and 56 minutes, concluding the radiation came from the Milky Way and was strongest toward the galaxy's center. Jansky's work helped distinguish between the radio sky and the optical sky.
Later, in 1963, American physicist and radio astronomer Arno Allan Penzias discovered cosmic microwave background radiation. In 1964, Penzias and his partner Robert Woodrow Wilson, using the ultra-sensitive Holmdel Horn Antenna, detected an unexplained radio noise. After contacting Robert Dicke, they identified it as the background radiation predicted by cosmological theories, a radio remnant of the Big Bang. They won the Nobel Prize in Physics in 1978.
NASA's Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE) is a device designed to observe the transition out of the 'cosmic dark ages' as the first stars ignite. It consists of 7 precision radiometers carried by a scientific research balloon to over 35 km altitude, measuring the tiny heating of the early universe by the first generation of stars and galaxies.
Reader's Guide
Cosmic noise is significant as it encompasses the background radio frequency radiation from galactic sources, including the cosmic microwave background radiation that helped establish the Big Bang theory. Karl Jansky's discovery of radio waves from the Milky Way in 1931 marked the birth of radio astronomy, distinguishing the radio sky from the optical sky. The radio sky includes daytime meteors, solar bursts, quasars, and gravitational waves. Penzias and Wilson's detection of CMBR in 1964 provided crucial evidence for the Big Bang, earning them the Nobel Prize. Cosmic noise also includes contributions from solar flares, which cause sudden bursts of absorption in Earth's ionosphere, and solar wind, which can cause sudden bursts of cosmic noise absorption detectable only if geomagnetic perturbations are large enough. NASA's ARCADE project furthers understanding of the early universe by measuring the heating from the first stars. The study of cosmic noise thus spans from the origins of the universe to ongoing solar and galactic phenomena, influencing both cosmology and radio astronomy.
Did You Know?
- Karl Jansky first discovered radio waves from the Milky Way in August 1931.
- Cosmic microwave background radiation is thought to be a relic of the Big Bang.
- Penzias and Wilson won the Nobel Prize in Physics in 1978 for discovering CMBR.
- ARCADE consists of 7 precision radiometers carried to an altitude of over 35 km by a scientific research balloon.
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