Find the word definition


n. A non-SI unit (symbol ''Jy'') measuring electromagnetic flux density equal to 10-26 watts per square meter per hertz.


The jansky (symbol Jy) is a non- SI unit of spectral flux density, or spectral irradiance, used especially in radio astronomy. It is equivalent to 10 watts per square metre per hertz.

The flux density or monochromatic flux, S, of a source is the integral of the spectral radiance, B, over the source solid angle:

S = ∬B(θ, ϕ)dΩ

The unit is named after pioneering US radio astronomer Karl Guthe Jansky, and is defined as:

$1 \ \mathrm{ Jy} = 10^{-26} \frac{ \mathrm{W} }{ \mathrm{m^2} \cdot \mathrm{Hz} }$ ( SI) $= 10^{-23} \frac{\mathrm{erg}}{ \mathrm{s} \cdot \mathrm{cm^2} \cdot \mathrm{Hz} }$ ( cgs)

Since the jansky is obtained by integrating over the whole source solid angle, it is most simply used to describe point sources; for example, the Third Cambridge Catalogue of Radio Sources (3C) reports results in Jy.

  • For extended sources, the surface brightness is often described with units of Jy per solid angle; for example, Far Infra-Red (FIR) maps from the IRAS satellite are in MJy/ sr.
  • Although extended sources at all wavelengths can be reported with these units, for radio frequency maps, extended sources have traditionally been described in terms of a brightness temperature; for example the [ Haslam et al.] 408 MHz all-sky continuum survey is reported in terms of a brightness temperature in K.
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. The visibility is also affected by libration, which can completely conceal this formation from view.

This is a worn crater with an eroded rim. The southern part of the rim in particular is disrupted and irregular in form, with a pair of small craters along the inner wall. The remainder of the rim is roughly circular. The interior floor is relatively featureless, except for a few tiny craterlets.

Jansky (disambiguation)

Jansky is a non-SI unit of electromagnetic flux.

Jansky or Janský may also refer to:

  • 1932 Jansky, a main belt asteroid
  • Jansky (crater), a lunar crater
  • Jansky (band), electroverse duet
Jansky (surname)

Jánský, less commonly accented Janský, is a Czech-language surname.

Some notable people with the surname include:

  • Peter Jánský, Czech hockey player
  • Jan Janský, Czech serologist, neurologist and psychiatrist, credited with the first classification of blood into the 4 types
  • Markéta Jánská (born 1981), Czech model
  • Karl Guthe Jansky, American physicist, radio engineer and discoverer of radio waves emanating from the Milky Way

Usage examples of "jansky".

It was bizarre occurrences in the shifting fields of space-time like the Jansky Singularity that were the real hazards.

So far, he had been buoyed up by the excitement of the Jansky Station project.

Board of Space Hazards commissioned the Jansky permanent outpost, Buchanan seemed to have regained his self-assurance.

What lay at the core of the enigma that was called the Jansky Singularity?

Only the Committee has the power to promote investigations of the Jansky Singularity, you see.

Board for the Regulation of Space Hazards turned out for the launching of the Jansky Singularity Station.

More than ever, he was sure he had been right to seize the opportunity presented by the building of the Jansky Station.

And still the robotic controller pointed out that it was his task to report on the Jansky Singularity, not to enter it.

And you, Commander Buchanan, are the commander of the Jansky Singularity Station.

He had not slept at all since the first sighting of the Jansky Singularity by the long-range scanners, and not much for days before that.

They were all to rendezvous at the raging efflorescence of the Jansky Singularity.

Liz Deffant was drifting away, silently spinning into the eerie depths of the Jansky Singularity.

Skills acquired in years of infragalactic flight among the reefs of hyper-space enabled him to squeeze the Jansky Station nearer and nearer the fraying transport.

And, at last, there was reciprocal contact with the Jansky Singularity Station.

Buchanan was sure he was asleep before the chute took him to the bridge of the Jansky Station.