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PowerPedia:Jansky

Lasted edited by Andrew Munsey, updated on June 14, 2016 at 10:10 pm.

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In There was an error working with the wiki: Code[4] There was an error working with the wiki: Code[20] equivalent to 10&minus26 Watts per There was an error working with the wiki: Code[21] per There was an error working with the wiki: Code[22].

SI unit description

The unit "jansky" is named after the pioneering radio astronomer There was an error working with the wiki: Code[5]. The brightest natural radio sources have flux densities of the order of one (to one hundred) janskies, which makes the jansky a suitable unit for There was an error working with the wiki: Code[23]. For example the Third Cambridge Catalogue (There was an error working with the wiki: Code[24]) which was prepared in 1959 and revised in 1962, lists some 300 to 400 radio sources in the Northern Hemisphere brighter than 9 Jy at 159 MHz.

: 1 Jy = 10-26 W m-2 Hz-1 (SI)

: 1 Jy = 10-23 erg s-1 cm-2 Hz-1 (There was an error working with the wiki: Code[6])

The flux density in Jy can be converted to a magnitude basis, for suitable assumptions about the spectrum. For instance, converting an There was an error working with the wiki: Code[25] to a flux-density in microjanskies is straightforward:{{cite journal | author=M. Fukugita

| title=Galaxy Colors in Various Photometric Band Systems | journal=PASP | year=1995 | volume=107 | pages=945-958}}

: Fv [&microJy] = 1029 10-(AB+48.6)/2.5

Unit naming

In honor of Karl Guthe Jansky, the unit used by radio astronomers for the strength (or There was an error working with the wiki: Code[7] on the There was an error working with the wiki: Code[8] There was an error working with the wiki: Code[26] fellowship program is named after Jansky.

Karl Guthe Jansky

Karl Guthe Jansky (There was an error working with the wiki: Code[9] There was an error working with the wiki: Code[10] site in There was an error working with the wiki: Code[27], near a reconstructed version of Grote Reber's 30m dish.

Early life

Jansky was born in There was an error working with the wiki: Code[11] of There was an error working with the wiki: Code[12] in There was an error working with the wiki: Code[13] site in There was an error working with the wiki: Code[14] and There was an error working with the wiki: Code[15] properties using "There was an error working with the wiki: Code[16]) for use in transatlantic There was an error working with the wiki: Code[17] that might interfere with radio voice transmissions.

Radio astronomy

Jansky built an Antenna (electronics) designed to receive radio waves at a There was an error working with the wiki: Code[18] (wavelength about 14.6 meters). It was mounted on a turntable that allowed it to rotate 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 There was an error working with the wiki: Code[28] 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 There was an error working with the wiki: Code[19].

His discovery was widely publicized, appearing in the There was an error working with the wiki: Code[29] of There was an error working with the wiki: Code[30], There was an error working with the wiki: Code[31]. 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 There was an error working with the wiki: Code[32] 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 There was an error working with the wiki: Code[33], 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 There was an error working with the wiki: Code[34], a radio engineer who singlehandedly built a There was an error working with the wiki: Code[35] in his There was an error working with the wiki: Code[36] back yard in There was an error working with the wiki: Code[37] and did the first systematic survey of astronomical radio waves. The second was Prof. John Kraus, who, after There was an error working with the wiki: Code[38], started a radio observatory at There was an error working with the wiki: Code[39] and wrote a textbook on radio astronomy, still considered a standard by many radio astronomers.

References and external articles

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General

M. Fukugita (1995). "Galaxy Colors in Various Photometric Band Systems". PASP 107: 945-958.

My Brother Karl Jansky and His Discovery of Radio Waves from Beyond the Earth

The Jansky Monument

F. Ghigo, Karl Jansky and the Discovery of Cosmic Radio Waves, National Radio Astronomy Observatory, 2006-02-07

There was an error working with the wiki: Code[1], Wikipedia: The Free Encyclopedia. Wikimedia Foundation.

jansky or flux unit unit of luminous flux used by radio astronomers.

Newsgroups

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See also

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