Editing Jansky (section)

== Usage ==
The flux to which the jansky refers can be in any form of [[radiant energy]].

It was created for and is still most frequently used in reference to electromagnetic energy, especially in the context of radio astronomy.

The brightest [[astronomical radio source]]s have flux densities of the order of 1–100 janskys. For example, the [[Third Cambridge Catalogue of Radio Sources]] lists some 300 to 400 radio sources in the Northern Hemisphere brighter than 9&nbsp;Jy at 159&nbsp;MHz. This range makes the jansky a suitable unit for [[radio astronomy]].

[[Gravitational waves]] also carry energy, so their flux density can also be expressed in terms of janskys.  Typical signals on Earth are expected to be 10<sup>20</sup>&nbsp;Jy or more.<ref>{{cite journal |first1= B. S. |last1=Sathyaprakash |first2=Bernard F. |last2 = Schutz | title = Physics, Astrophysics and Cosmology with Gravitational Waves |journal=Living Reviews in Relativity |date=2009-03-04 |volume=12 |issue=1 |page=2 |doi=10.12942/lrr-2009-2 |doi-access=free |pmid=28163611 |pmc=5255530 |arxiv=0903.0338 |bibcode=2009LRR....12....2S }}</ref>  However, because of the poor coupling of gravitational waves to matter, such signals are difficult to detect.

When measuring broadband continuum emissions, where the energy is roughly evenly distributed across the detector [[Bandwidth (signal processing)|bandwidth]], the detected signal will increase in proportion to the bandwidth of the detector (as opposed to signals with bandwidth narrower than the detector bandpass). To calculate the flux density in janskys, the total power detected (in watts) is divided by the receiver collecting area (in square meters), and then divided by the detector bandwidth (in hertz).  The flux density of astronomical sources is many orders of magnitude below 1&nbsp;W·m<sup>−2</sup>·Hz<sup>−1</sup>, so the result is multiplied by 10<sup>26</sup> to get a more appropriate unit for natural astrophysical phenomena.<ref>
{{cite web
 | author= Ask SETI
 | publisher = SETI League
 | title = Research: Understanding the Jansky
 | url=http://www.setileague.org/askdr/jansky.htm
 | date=2004-12-04
 | access-date = 2007-06-13
}}</ref>

The millijansky, mJy, was sometimes referred to as a milli-flux unit (mfu) in older astronomical literature.<ref name=Ross75>
{{cite journal
 | last=Ross |first=H.N.
 | title= Variable radio source structure on a scale of several minutes of arc
 | journal=The Astrophysical Journal
 | year=1975
 | volume=200
 | page=790
 | bibcode=1975ApJ...200..790R|doi = 10.1086/153851 |doi-access=free
}}</ref>