<p>Excellent question! There is no general concensus on how to name things. Usually <span class="math-container">$V$</span> refers in this context to the visual magnitude. Any index... usually will need explaining. In this particular case it's different sources most likely assigning a slightly different symbol to the same thing.</p>
<p>Thus I assume you are referring to how for the same star a different magnitude is given in different resources / websites? The difference (in this particular case) is not explicable by the fact that it's a multiple star system and eclipses might occur.</p>
<p>If so: the difference is not huge and I'd attribute that to different measurements. Let's dive in deeper and have a closer look at the references. This seems right when one looks at the references they quote:
The somewhat canonical source in astrophysics is <a href="http://simbad.u-strasbg.fr/simbad/sim-id?Ident=mintaka" rel="nofollow noreferrer">Sinbad</a> which allows to get an overview of references for a certain source. This quotes 2.41 as visual magnitude for Mintaka. Your first source seems to use this as reference, too.</p>
<p>Your second source quotes a slightly brighter value and references the older 1997 version of the Tycho Brahe catalogue as source. And indeed, if I <a href="https://vizier.cds.unistra.fr/viz-bin/VizieR-5?-ref=VIZ62f23bb23d3c96&amp;-out.add=.&amp;-source=I/239/tyc_main&amp;recno=512645" rel="nofollow noreferrer">query that</a> for &quot;delta Orionis&quot;, it gives a visual magnitude of 2.23.</p>
<p>So in essence: what you see is that there is not an absolute truth. Every measurement has measurement uncertainties. Subsequent measurements may refine the values measured (or maybe the star changed - but so much is unlikely here). It uses different instruments to get to a result which need proper cross-calibration. Maybe (some of) the difference can be explained that way. So... whom to trust? Difficult. Both sources are reputable, both went through peer review. I'd use the one from the newer catalogue.</p>

CC BY-SA 4.0
2022-08-09T12:35:49.253Z
Thank you very much.
Elena Greg
CC BY-SA 4.0
2022-08-09T15:00:08.053Z
Simbad isn't a source. The source is the Tycho double star catalogue from 2002.
ProfRob
CC BY-SA 4.0
2022-08-09T11:03:27.263Z
2022-08-09T11:03:27.263Z
planetmaker
<p>Does <span class="math-container">$V_0$</span> stand for the magnitude during a primary eclipse and <span class="math-container">$V$</span> for magnitude during no eclipse?</p>
<p>For instance, <a href="https://www.stelledoppie.it/index2.php?iddoppia=20126" rel="nofollow noreferrer">here</a> is the magnitude of 2.41 and <a href="https://in-the-sky.org/data/object.php?id=TYC4766-2445-1" rel="nofollow noreferrer">here</a> the magnitude of 2.23. I saw the notation <span class="math-container">$V_0 = 2.41$</span> and <span class="math-container">$V = 2.23$</span>.</p>
<p>Thank you</p>

<magnitude>
Visual magnitude - V_0 and V difference
Elena Greg
# Visual magnitude - V_0 and V difference

(Asked by: username_0 on 2022-08-09)

Does $V\_0$ stand for the magnitude during a primary eclipse and $V$ for magnitude during no eclipse?

For instance, [here](https://www.stelledoppie.it/index2.php?iddoppia=20126) is the magnitude of 2.41 and [here](https://in-the-sky.org/data/object.php?id=TYC4766-2445-1) the magnitude of 2.23. I saw the notation $V\_0 = 2.41$ and $V = 2.23$.

Thank you

**Tags:** magnitude

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## 1 answers

### Answer by username_1 on 2022-08-09. Score: 3 | Accepted answer

Excellent question! There is no general concensus on how to name things. Usually $V$ refers in this context to the visual magnitude. Any index... usually will need explaining. In this particular case it's different sources most likely assigning a slightly different symbol to the same thing.

Thus I assume you are referring to how for the same star a different magnitude is given in different resources / websites? The difference (in this particular case) is not explicable by the fact that it's a multiple star system and eclipses might occur.

If so: the difference is not huge and I'd attribute that to different measurements. Let's dive in deeper and have a closer look at the references. This seems right when one looks at the references they quote:
The somewhat canonical source in astrophysics is [Sinbad](http://simbad.u-strasbg.fr/simbad/sim-id?Ident=mintaka) which allows to get an overview of references for a certain source. This quotes 2.41 as visual magnitude for Mintaka. Your first source seems to use this as reference, too.

Your second source quotes a slightly brighter value and references the older 1997 version of the Tycho Brahe catalogue as source. And indeed, if I [query that](https://vizier.cds.unistra.fr/viz-bin/VizieR-5?-ref=VIZ62f23bb23d3c96&-out.add=.&-source=I/239/tyc_main&recno=512645) for "delta Orionis", it gives a visual magnitude of 2.23.

So in essence: what you see is that there is not an absolute truth. Every measurement has measurement uncertainties. Subsequent measurements may refine the values measured (or maybe the star changed - but so much is unlikely here). It uses different instruments to get to a result which need proper cross-calibration. Maybe (some of) the difference can be explained that way. So... whom to trust? Difficult. Both sources are reputable, both went through peer review. I'd use the one from the newer catalogue.

> **Comments:**
> **username_0**: Thank you very much.  
> **username_2**: Simbad isn't a source. The source is the Tycho double star catalogue from 2002.  

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