Talk:Jansky

Untitled

The material formerly here appeared to be a copy of information from http://www.unc.edu/~rowlett/units/dictJ.html, so I have replaced it by a stub.

Not quite correct to say 1Jy is bright - it wouldn't have made 3C! - altered slightly.Linuxlad 12:42, 12 Mar 2005 (UTC)

Plural form

In the texts I've read, the plural form of 'jansky' is hardly ever written 'janskies'. In most cases, the singular form is retained, especially in phrases like '22 jansky' or '450 microjansky'. Any thoughts on a convention that should be adopted in this article?
MHD 20:07, 30 January 2006 (UTC)

AB

You need a link out to this (I presume it's absolute brightness/magnitude). Linuxlad 11:10, 31 January 2006 (UTC)

I'll check whether this is indeed the kind of magnitude that should be linked to in this context, there are tons of different ways to determine the magnitude of a system. I'll be around some real astronomers during the rest of the day, I'll get back to this. MHD 10:52, 2 February 2006 (UTC)

Well the exponent (M/2.5) is clearly right so it's just the constant (for some given assumptions on the effective bandwidth?). I read somewhere that zeroth Magnitude is 630 Jy, (in which case this could be about a factor 2 out?) Linuxlad

Correct, the exponent is the same. AB magnitudes, as I understand it, is a different kind of magnitudes scale, based on the fact that one particular star (Vega), has a magnitude of 0 in every color band. In this way, the color of every other object in the sky can be related to the 'zero-color' based on Vega. There is not an article on Wikipedia yet about AB magnitudes. MHD 12:31, 2 February 2006 (UTC)

OK, I've edited to provide a lead-in sentence, and a redlink to AB magnitude. Over to you (I've done enogh damage for today :-))Linuxlad

AB magnitudes are not based on Vega. In the Vega magnitude system, Vega's flux density in any color band defines magnitude of zero. In the AB magnitude system, magnitude of zero always corresponds to 3.631e-20 erg/s/cm^2/Hz, which is 3631 Jy. 68.231.145.131 05:34, 5 May 2007 (UTC)

Flux Density

Radiometric flux generally refers to a unit like Watts, similar to Luminosity. Flux density is specific in terms of frequency/wavelength. See Rieke's Detection of Light, for example.

Don't know about nowadays, but many years ago they were definitely called 'flux units'. Bob aka Linuxlad

Hmm, I guess it's most important to be consistent with Wikipedia, I should look around and see what wikipedia says.

Though I agree that flux density unit would be a better name (since it is a flux per unit wavelength (or frequency)), I have never seen or heard anyone (in the field of astronomy/astrophysics) refer to this unit as flux density unit. I think we should stick with the historical name flux unit (sometimes abbreviated fu, seriously). People who look this up in an encyclopedia or on Wikipedia will want to know what the 'experts' mean when they talk about flux units. I don't know about other fields of science, but I am pretty sure that astronomers used to say flux unit (it's kind of a deprecated term now I guess), not flux density unit. Cheers, MHD 10:08, 13 March 2006 (UTC)

'Flux unit' is an archaic synonym for Jansky. However, Janskys are a unit of flux density (flux per frequency or flux per wavelength), in the same way that ergs are a unit of energy. Janskys are not a unit of flux. Does that make it clearer? 68.231.145.131 05:29, 5 May 2007 (UTC)

Stub

I don't think it still deserves a stub label, should they be removed? - Eoin 20:15, 20 May 2007 (UTC)

I've gone ahead and changed it to start class. →Σσς. (Sigma) 03:34, 26 February 2013 (UTC)

Checking the calculations in the table

I think there is an error in the examples table. The first entry, about the cell phone interference, provides all the data to do the calculation, and it turns out a factor 2 larger. Maybe this is due to taking into account the reflection on the ground or that the emission is not spherical? This should be explicitated. - 165.132.36.156 (talk) 03:10, 25 October 2013 (UTC)

Orders of magnitude table

This is a request for someone with the relevant knowledge and/or sources to add some lines to the table for lower orders of magnitude that cover the usual objects of radio astronomy. List of fast radio bursts, for example, gives values between 0.3 and 30 Jy. Beorhtwulf (talk) 19:13, 10 January 2019 (UTC)

What's the motivation?

What's the "reason" for using Janskys? The article points out that they are non-SI, so I was wondering what makes them convenient or useful, "why" use them? I'm not saying they are not useful, asking what makes them convenient. Was it the 1-100 scale for redio sources? Feldercarb (talk) 21:05, 24 July 2023 (UTC)

Historically, many of the earliest detected astronomical radio sources had a brightness of about a jansky. These days, we can detect sources in the nanojansky range (the single 30s image depth for the Rubin Observatory LSST in optical bands will be about 575 nJy, while JWST's deep fields will be in the 10s of nJy or better). We should get a citation or two (probably needs to be a textbook) with some of that history in here. - Parejkoj (talk) 15:48, 25 July 2023 (UTC)