Karl Guthe Jansky
Encyclopedia
Karl Guthe Jansky was an American
physicist
and radio
engineer
who in August 1931 first discovered radio wave
s emanating from the Milky Way
. He is considered one of the founding figures of radio astronomy
.
. Dean Jansky, born in Wisconsin of Czech immigrants, had started teaching at the age of sixteen. He was a teacher throughout his active life, retiring as Professor of Electrical Engineering at the University of Wisconsin. He was an engineer with a strong interest in physics, a trait passed on to his sons. Karl Jansky was named after Dr. Karl Guthe, who had been an important mentor to Cyril M. Jansky.
Karl Jansky's mother, née Nellie Moreau, was of French and English descent. Karl's brother Cyril Jansky Jr., who was ten years older, helped build some of the earliest radio transmitters in the country, including 9XM in Wisconsin
(now WHA
of Wisconsin Public Radio
) and 9XI in Minnesota
(now KUOM
).
Karl Jansky attended college at the University of Wisconsin–Madison
where he received his BS
in physics
in 1927. In 1928 he joined the Bell Telephone Laboratories
site in Holmdel, New Jersey. Bell Labs wanted to investigate atmospheric
and ionospheric
properties using "short waves" (wavelength
s of about 10-20 meters) for use in transatlantic radio telephone service. As a radio engineer, Jansky was assigned the job of investigating sources of static that might interfere with radio voice transmissions.
of 20.5 MHz (wavelength about 14.6 meters). (Location: 40°21′54"N 74°9′48"W) It was mounted on a turntable that allowed it to be rotated in any direction, earning it the name "Jansky's merry-go-round". It had a diameter of approximately 100 ft. and stood 20 ft. tall. By rotating the antenna on a set of four Ford Model-T tires, the direction of a received signal could be pinpointed. A small shed to the side of the antenna housed an analog
pen-and-paper recording system.
After recording signals from all directions for several months, Jansky eventually categorized them into three types of static: nearby thunderstorms, distant thunderstorms, and a faint steady hiss of unknown origin. He spent over a year investigating the source of the third type of static. The location of maximum intensity rose and fell once a day, leading Jansky to initially surmise that he was detecting radiation from the Sun.
After a few months of following the signal, however, the brightest point moved away from the position of the Sun. Jansky also determined that the signal repeated on a cycle of 23 hours and 56 minutes, the period of the Earth's rotation relative to the cosmos
(sidereal day), instead of the 24-hour solar day. By comparing his observations with optical astronomical maps, Jansky concluded that the radiation was coming from the Milky Way
and was strongest in the direction of the center the galaxy, in the constellation
of Sagittarius
.
His discovery was widely publicized, appearing in the New York Times of May 5, 1933. He published his classic paper "Electrical disturbances apparently of extraterrestrial origin" in Proc. IRE in 1933. This paper was re-printed in Proc. IEEE in 1984 (for their centennial issue, where they note the research most likely would have won a Nobel prize, had not the author died young) and again in 1998, for the first centennial of radio. Jansky wanted to follow up on this discovery and investigate the radio waves from the Milky Way in further detail. He submitted a proposal to Bell Labs to build a 30 meter diameter dish antenna with greater sensitivity that would allow more careful measurements of the structure and strength of the radio emission. Bell Labs, however, rejected his request for funding on the grounds that the detected emission would not significantly affect their planned transatlantic communications system. Jansky was re-assigned to another project and did no further work in the field of astronomy.
, and observatories were wary of taking on any new and potentially risky projects.
Two men who learned of Jansky's 1933 discovery were of great influence on the later development of the new study of radio astronomy: one was Grote Reber
, a radio engineer who singlehandedly built a radio telescope
in his Illinois
back yard in 1937 and did the first systematic survey of astronomical radio waves. The second was Prof. John D. Kraus
, who, after World War II
, started a radio observatory at Ohio State University
and wrote a textbook on radio astronomy, long considered a standard by radio astronomers.
) of radio sources is the jansky
(1 Jy = 10−26 W m−2 Hz−1). The crater Jansky
on the Moon
is also named after him. The NRAO
postdoctoral fellowship program is named after Karl Jansky. Additionally, NRAO awards the Jansky Prize annually in Jansky's honor.
A full-scale replica of Jansky's original rotating telescope is located on the grounds of the NRAO
site in Green Bank, West Virginia
, near a reconstructed version of Grote Reber's 9m dish.
The original site of Jansky's antenna (40.365175 deg. N, 74.163705 deg. W) was determined by Lucent Technologies
(the successor of Bell Telephone Laboratories) in the 1990s, and a plaque was placed there honoring the achievement. The original site is located at 101 Crawfords Corner Road, Holmdel, New Jersey.
Jansky noise is named after Jansky, and refers to high frequency
static disturbances
of cosmic
origin.
Jansky was a resident of Little Silver, New Jersey
, and died at age 44 in a Red Bank, New Jersey
hospital due to a heart condition.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
physicist
Physicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...
and radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
engineer
Engineer
An engineer is a professional practitioner of engineering, concerned with applying scientific knowledge, mathematics and ingenuity to develop solutions for technical problems. Engineers design materials, structures, machines and systems while considering the limitations imposed by practicality,...
who in August 1931 first discovered radio wave
Radio Wave
Radio Wave may refer to:*Radio frequency*Radio Wave 96.5, a radio station in Blackpool, UK...
s emanating from the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
. He is considered one of the founding figures of radio astronomy
Radio astronomy
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...
.
Early life
Karl Guthe Jansky was born in what was then the Territory of Oklahoma where his father, Cyril M. Jansky, was Dean of the College of Engineering at the University of Oklahoma at NormanUniversity of Oklahoma
The University of Oklahoma is a coeducational public research university located in Norman, Oklahoma. Founded in 1890, it existed in Oklahoma Territory near Indian Territory for 17 years before the two became the state of Oklahoma. the university had 29,931 students enrolled, most located at its...
. Dean Jansky, born in Wisconsin of Czech immigrants, had started teaching at the age of sixteen. He was a teacher throughout his active life, retiring as Professor of Electrical Engineering at the University of Wisconsin. He was an engineer with a strong interest in physics, a trait passed on to his sons. Karl Jansky was named after Dr. Karl Guthe, who had been an important mentor to Cyril M. Jansky.
Karl Jansky's mother, née Nellie Moreau, was of French and English descent. Karl's brother Cyril Jansky Jr., who was ten years older, helped build some of the earliest radio transmitters in the country, including 9XM in Wisconsin
Wisconsin
Wisconsin is a U.S. state located in the north-central United States and is part of the Midwest. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michigan to the northeast, and Lake Superior to the north. Wisconsin's capital is...
(now WHA
WHA (AM)
-External links:*Jeff Miller . *Randall Davidson. PortalWisconsin.org...
of Wisconsin Public Radio
Wisconsin Public Radio
Wisconsin Public Radio is a network of 32 radio stations in the state of Wisconsin. WPR's network is divided into two distinct analog services, the Ideas Network and the NPR News and Classical Network, as well as the "HD2 Classical Service," a digital-only, full-time classical music service.-Ideas...
) and 9XI in Minnesota
Minnesota
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...
(now KUOM
KUOM
KUOM, known as "770 Radio K", "Real College Radio" is a college radio station operated by the University of Minnesota Twin Cities. Likely the oldest station in the state, Radio K broadcasts an eclectic mix of music from its transmitters—a variety that has been praised by radio critics...
).
Karl Jansky attended college at the University of Wisconsin–Madison
University of Wisconsin–Madison
The University of Wisconsin–Madison is a public research university located in Madison, Wisconsin, United States. Founded in 1848, UW–Madison is the flagship campus of the University of Wisconsin System. It became a land-grant institution in 1866...
where he received his BS
Bachelor of Science
A Bachelor of Science is an undergraduate academic degree awarded for completed courses that generally last three to five years .-Australia:In Australia, the BSc is a 3 year degree, offered from 1st year on...
in physics
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
in 1927. In 1928 he joined the Bell Telephone Laboratories
Bell Labs
Bell Laboratories is the research and development subsidiary of the French-owned Alcatel-Lucent and previously of the American Telephone & Telegraph Company , half-owned through its Western Electric manufacturing subsidiary.Bell Laboratories operates its...
site in Holmdel, New Jersey. Bell Labs wanted to investigate atmospheric
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
and ionospheric
Ionosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
properties using "short waves" (wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
s of about 10-20 meters) for use in transatlantic radio telephone service. As a radio engineer, Jansky was assigned the job of investigating sources of static that might interfere with radio voice transmissions.
Radio astronomy
At Bell Telephone Laboratories Jansky built an antenna designed to receive radio waves at a frequencyFrequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
of 20.5 MHz (wavelength about 14.6 meters). (Location: 40°21′54"N 74°9′48"W) It was mounted on a turntable that allowed it to be rotated in any direction, earning it the name "Jansky's merry-go-round". It had a diameter of approximately 100 ft. and stood 20 ft. tall. By rotating the antenna on a set of four Ford Model-T tires, the direction of a received signal could be pinpointed. A small shed to the side of the antenna housed an analog
Analog signal
An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
pen-and-paper recording system.
After a few months of following the signal, however, the brightest point moved away from the position of the Sun. Jansky also determined that the signal repeated on a cycle of 23 hours and 56 minutes, the period of the Earth's rotation relative to the cosmos
Cosmos
In the general sense, a cosmos is an orderly or harmonious system. It originates from the Greek term κόσμος , meaning "order" or "ornament" and is antithetical to the concept of chaos. Today, the word is generally used as a synonym of the word Universe . The word cosmos originates from the same root...
(sidereal day), instead of the 24-hour solar day. By comparing his observations with optical astronomical maps, Jansky concluded that the radiation was coming from the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
and was strongest in the direction of the center the galaxy, in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Sagittarius
Sagittarius (constellation)
Sagittarius is a constellation of the zodiac, the one containing the galactic center. Its name is Latin for the archer, and its symbol is , a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow...
.
His discovery was widely publicized, appearing in the New York Times of May 5, 1933. He published his classic paper "Electrical disturbances apparently of extraterrestrial origin" in Proc. IRE in 1933. This paper was re-printed in Proc. IEEE in 1984 (for their centennial issue, where they note the research most likely would have won a Nobel prize, had not the author died young) and again in 1998, for the first centennial of radio. Jansky wanted to follow up on this discovery and investigate the radio waves from the Milky Way in further detail. He submitted a proposal to Bell Labs to build a 30 meter diameter dish antenna with greater sensitivity that would allow more careful measurements of the structure and strength of the radio emission. Bell Labs, however, rejected his request for funding on the grounds that the detected emission would not significantly affect their planned transatlantic communications system. Jansky was re-assigned to another project and did no further work in the field of astronomy.
Follow-up
Several scientists were interested by Jansky's discovery, but radio astronomy remained a dormant field for several years, due in part to Jansky's lack of formal training as an astronomer. His discovery had come in the midst of the Great DepressionGreat Depression
The Great Depression was a severe worldwide economic depression in the decade preceding World War II. The timing of the Great Depression varied across nations, but in most countries it started in about 1929 and lasted until the late 1930s or early 1940s...
, and observatories were wary of taking on any new and potentially risky projects.
Two men who learned of Jansky's 1933 discovery were of great influence on the later development of the new study of radio astronomy: one was Grote Reber
Grote Reber
Grote Reber was an amateur astronomer and pioneer of radio astronomy. He was instrumental in investigating and extending Karl Jansky's pioneering work, and conducted the first sky survey in the radio frequencies...
, a radio engineer who singlehandedly built a radio telescope
Radio telescope
A radio telescope is a form of directional radio antenna used in radio astronomy. The same types of antennas are also used in tracking and collecting data from satellites and space probes...
in his Illinois
Illinois
Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...
back yard in 1937 and did the first systematic survey of astronomical radio waves. The second was Prof. John D. Kraus
John D. Kraus
John Daniel Kraus was an American physicist known for his contributions to electromagnetics, radio astronomy, and antenna theory. His inventions included the helical antenna, the corner reflector, and several other types of antennas...
, who, after World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, started a radio observatory at Ohio State University
Ohio State University
The Ohio State University, commonly referred to as Ohio State, is a public research university located in Columbus, Ohio. It was originally founded in 1870 as a land-grant university and is currently the third largest university campus in the United States...
and wrote a textbook on radio astronomy, long considered a standard by radio astronomers.
Legacy
In honor of Jansky, the unit used by radio astronomers for the strength (or flux densityFlux density
-Formal Statement:The flux density is simply defined as the amount of flux passing through a unit-area. -Mathematical Statement:The flux density would essentially be the number of field lines passing through a defined unit-area...
) of radio sources is the jansky
Jansky
The flux unit or jansky is a non-SI unit of spectral flux density equivalent to 10−26 watts per square metre per hertz...
(1 Jy = 10−26 W m−2 Hz−1). The crater Jansky
Jansky (crater)
Jansky is a lunar impact crater that lies along the eastern limb of the Moon. It lies due east of the larger walled plain Neper, along the southern edge of the Mare Marginis. Due to its location, this crater is viewed from the side from Earth, limiting the amount of detail that can be observed...
on the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
is also named after him. The NRAO
National Radio Astronomy Observatory
The National Radio Astronomy Observatory is a Federally Funded Research and Development Center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc for the purpose of radio astronomy...
postdoctoral fellowship program is named after Karl Jansky. Additionally, NRAO awards the Jansky Prize annually in Jansky's honor.
A full-scale replica of Jansky's original rotating telescope is located on the grounds of the NRAO
National Radio Astronomy Observatory
The National Radio Astronomy Observatory is a Federally Funded Research and Development Center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc for the purpose of radio astronomy...
site in Green Bank, West Virginia
Green Bank, West Virginia
Green Bank is a census-designated place in Pocahontas County in West Virginia's Potomac Highlands inside the Allegheny Mountain Range. Green Bank is located along WV 28. Green Bank is also close to the Snowshoe Mountain ski resort...
, near a reconstructed version of Grote Reber's 9m dish.
The original site of Jansky's antenna (40.365175 deg. N, 74.163705 deg. W) was determined by Lucent Technologies
Lucent Technologies
Alcatel-Lucent USA, Inc., originally Lucent Technologies, Inc. is a French-owned technology company composed of what was formerly AT&T Technologies, which included Western Electric and Bell Labs...
(the successor of Bell Telephone Laboratories) in the 1990s, and a plaque was placed there honoring the achievement. The original site is located at 101 Crawfords Corner Road, Holmdel, New Jersey.
Jansky noise is named after Jansky, and refers to high frequency
High frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
static disturbances
Noise (radio)
In radio reception, noise is the superposition of white noise and other disturbing influences on the signal, caused either by thermal noise and other electronic noise from receiver input circuits or by interference from radiated electromagnetic noise picked up by the receiver's antenna...
of cosmic
COSMIC
Constellation Observing System for Meteorology, Ionosphere, and Climate is a program designed to provide advances in meteorology, ionospheric research, climatology, and space weather by using GPS satellites in conjunction with low Earth orbiting satellites...
origin.
Jansky was a resident of Little Silver, New Jersey
Little Silver, New Jersey
Little Silver is a borough in Monmouth County, New Jersey, United States. As of the 2010 United States Census, the borough population was 5,950.Little Silver was established with a Kings Land Grant in 1663 and settled in 1667...
, and died at age 44 in a Red Bank, New Jersey
Red Bank, New Jersey
-Demographics:As of the census of 2000, there were 11,844 people, 5,201 households, and 2,501 families residing in the borough. The population density was 6,639.1 people per square mile . There were 5,450 housing units at an average density of 3,055.0 per square mile...
hospital due to a heart condition.
Selected writings
- 1932: Directional studies of atmospherics at high frequencies, Proc. IRE, 20, p. 1920.
- 1933: Electrical disturbances apparently of extraterrestrial origin, Proc. IRE, 21, p. 1387. ( in Proc. IEEE, vol. 86, no. 7 (July 1998), pp. 1510-1515.) Published with the reprint is an explanatory article .
- 1933: "Radio waves from outside the solar system", Nature, 132, p. 66.
- 1933: "Electrical phenomena that apparently are of interstellar origin", Popular Astronomy, 41, p. 548, Dec., 1933.
- 1935: A note on the source of interstellar interference, Proc. IRE, 23, p. 1158.
- 1937: Minimum noise levels obtained on short-wave radio receiving systems, Proc. IRE, 25, p. 1517.
External links
- My Brother Karl Jansky and His Discovery of Radio Waves from Beyond the Earth
- Historical Marker Database: Karl Jansky Radio Astronomy Monument
- Accompanying 3 photos: from 1962, from c.1960 (with Grote Reber), and one of Karl Jansky, another astronomy pioneer, from c.1930.
- Encyclopedia of Oklahoma History and Culture - Jansky, Karl
- http://www.nrao.edu/whatisra/hist_jansky.shtml
- http://www.bell-labs.com/news/1998/june/4/2.html