<p>In the documentation of Simbad, it is written:
The magnitudes in Simbad are not always given in a single system. For instance, the &quot;K&quot; band includes K K' and Ks. For more details check the bibliographical reference and the SVO profile filter service : <a href="http://svo2.cab.inta-csic.es/theory/fps/" rel="nofollow noreferrer">http://svo2.cab.inta-csic.es/theory/fps/</a>.</p>
<p>Magnitudes are given, when possible, in the Johnson's UBV system. Otherwise, the (AB) flag is given if it cames from a AB system.</p>

CC BY-SA 4.0
2022-06-03T05:05:06.113Z
2022-06-03T05:05:06.113Z
Anaïs OBERTO
<p>Each letter represents a filter that passes certain wavelengths of light and blocks others. The flux of the light that passes the filter is measured and that can be converted to a magnitude.</p>
<p>Some letters are mnemonic, so U is ultraviolet R, G, B are for Red, Green and Blue, and V is for Visual. I is a near-infrared filter, but more infrared filters were added and assigned letters J K L M and N,  then Z Y and (randomly) H were inserted, resulting in the current rather jumbled system. More details can be found at the <a href="https://en.wikipedia.org/wiki/Photometric_system#Photometric_letters" rel="nofollow noreferrer">Wikipedia article</a></p>
<p>Lower case letter are just a variant, the specific meaning of a filter may vary from telescope to telescope, and while you can get a general idea of whether an object is brighter in the UV or IR, you would need to read the original paper to find out exactly the characteristics of the filter used.</p>

CC BY-SA 4.0
2022-05-29T15:53:18.397Z
I might be wrong, but generally speaking, lower case filter names are often attached to narrower photometric bands. In this case, the Gunn system. But that might also be an accident.
ProfRob
CC BY-SA 4.0
2022-05-29T08:28:14.117Z
2022-05-29T08:36:34.310Z
2022-05-29T08:36:34.310Z
James K
<p>For any object on Simbad so lets take a random one,</p>
<p><a href="http://simbad.u-strasbg.fr/simbad/sim-id?Ident=ton%20618" rel="nofollow noreferrer">http://simbad.u-strasbg.fr/simbad/sim-id?Ident=ton%20618</a>  (Ton 618)</p>
<p>I'm trying to get a layman's explanation of Flux.</p>
<p>What do the letters stand for,</p>
<p>Does V stand for Visual and is it therefore the Apparent Magnitude of the object?  I see some pages on wikipedia saying &quot;Apparent Magnitude (v)&quot; and seemingly refer to the value in the Simbad page.</p>
<p>I look up in Google e.g. &quot;Flux Filter-name&quot; and don't get an explanation.</p>

CC BY-SA 4.0
2022-05-20T19:47:44.757Z
A place to start: https://en.wikipedia.org/wiki/Photometric_system#Photometric_letters
Jean-Marie Prival
CC BY-SA 4.0
2022-05-21T09:45:11.090Z
Thanks Jean-Marie, I wasn't aware of their group name.  I did some more research and found this "The B band was devised to approximate the raw photographic
magnitude (less the UV), whereas the V band was to approximate the visual magnitude system" in https://sites.astro.caltech.edu/~george/ay122/Bessel2005ARAA43p293.pdf so therefore assuming V does represent the visual magnitude
MiscellaneousUser
<flux><simbad>
What do the flux letters mean? (U, B, V, R, I, G, J, H, K, u, g, r, i, z)
MiscellaneousUser
# What do the flux letters mean? (U, B, V, R, I, G, J, H, K, u, g, r, i, z)

(Asked by: username_0 on 2022-05-20)

For any object on Simbad so lets take a random one,

<http://simbad.u-strasbg.fr/simbad/sim-id?Ident=ton%20618> (Ton 618)

I'm trying to get a layman's explanation of Flux.

What do the letters stand for,

Does V stand for Visual and is it therefore the Apparent Magnitude of the object? I see some pages on wikipedia saying "Apparent Magnitude (v)" and seemingly refer to the value in the Simbad page.

I look up in Google e.g. "Flux Filter-name" and don't get an explanation.

**Tags:** flux, simbad

> **Comments:**
> **username_1**: A place to start: https://en.wikipedia.org/wiki/Photometric_system#Photometric_letters  
> **username_0**: Thanks username_1, I wasn't aware of their group name.  I did some more research and found this "The B band was devised to approximate the raw photographic magnitude (less the UV), whereas the V band was to approximate the visual magnitude system" in https://sites.astro.caltech.edu/~george/ay122/Bessel2005ARAA43p293.pdf so therefore assuming V does represent the visual magnitude  

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## 2 answers

### Answer by username_2 on 2022-06-03. Score: 2

In the documentation of Simbad, it is written:
The magnitudes in Simbad are not always given in a single system. For instance, the "K" band includes K K' and Ks. For more details check the bibliographical reference and the SVO profile filter service : <http://svo2.cab.inta-csic.es/theory/fps/>.

Magnitudes are given, when possible, in the Johnson's UBV system. Otherwise, the (AB) flag is given if it cames from a AB system.


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### Answer by username_3 on 2022-05-29. Score: 2

Each letter represents a filter that passes certain wavelengths of light and blocks others. The flux of the light that passes the filter is measured and that can be converted to a magnitude.

Some letters are mnemonic, so U is ultraviolet R, G, B are for Red, Green and Blue, and V is for Visual. I is a near-infrared filter, but more infrared filters were added and assigned letters J K L M and N, then Z Y and (randomly) H were inserted, resulting in the current rather jumbled system. More details can be found at the [Wikipedia article](https://en.wikipedia.org/wiki/Photometric_system#Photometric_letters)

Lower case letter are just a variant, the specific meaning of a filter may vary from telescope to telescope, and while you can get a general idea of whether an object is brighter in the UV or IR, you would need to read the original paper to find out exactly the characteristics of the filter used.

> **Comments:**
> **username_4**: I might be wrong, but generally speaking, lower case filter names are often attached to narrower photometric bands. In this case, the Gunn system. But that might also be an accident.  

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