Talk:NML Cygni

A fact from NML Cygni appeared on Wikipedia's Main Page in the Did you know column on 30 August 2012. The text of the entry was as follows: Did you know... that the red supergiant NML Cygni is the largest star currently known, at about 1,650 times the Sun's diameter? A record of the entry may be seen at Wikipedia:Did you know archive/2012/August. The nomination discussion and review may be seen at Template:Did you know nominations/NML Cygni.

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The article says both that [The association] "has an estimated mass loss rate of 2×10^(−4) M⊙ yr ^(−1)" and that "The star has one of the largest mass loss rates at around 2 × 10^-4 M_☉ per year". Which is it? (I was going to fix the formatting of the first one but then noticed the second) —Lidnariq (talk) 22:52, 9 November 2012 (UTC)[reply]

The first statement gives a misleading impression that it is talking about the whole association when it is actually talking about just NML Cygni. Associations don't have mass loss rates. Mass loss rates are a hot research topic right now, partly because we suddnely have the technology to measure them but also because theory and observation don't match up, with the apparent evolution of stars requiring much high mass loss than we can observe. BTW, this is an extreme mass loss rate for a star, exceeded only in the most violent stars such as erupting luminous blue variables. The only red supergiant that comes close to this is VY CMa:

http://www.aanda.org/articles/aa/abs/2011/02/aa13993-10/aa13993-10.html Lithopsian (talk) 23:25, 9 November 2012 (UTC)[reply]

For anyone planning to expand or do work to this article - I have created a draft article over at my userspace which anyone is welcome to help contribute to. I will be transferring it here when enough work has been done to it. Samwalton9 (talk) 22:29, 24 June 2013 (UTC)[reply]

This is on hold for now, don't have the time, so don't worry about editing the article here. Samwalton9 (talk) 11:39, 22 August 2013 (UTC)[reply]

this article http://arxiv.org/abs/1207.1850 has been quoted as the source of the 1650 R_☉. however, i could not find 1650 R_☉ in the article. all i could find was the following sentence on page 10: NML Cyg’s stellar size of 16.2 mas from Blöcker et al.(2001) was derived using the Stepan-Boltzmann law, adopting Teff=2500 K and a distance of 1.74 kpc. Rescaling this stellar diameter with our distance of 1.61 kpc gives 15.0 mas. well, mas are milli arc seconds, i suppose.

using http://www.wolframalpha.com/input/?i=1.61+kpc*sin%2815+milliarcseconds%29 i get a diameter of 3.613 billion km. this is far from the 2.29 billion km for NML Cygni. can anyone explain, how the 1650 R_☉ were calculated? many thanks --Agentjoerg (talk) 04:29, 29 June 2014 (UTC)[reply]

The Stepan-Boltzmann Law is your friend. The luminosity and effective temperature define the size. The paper derives the effective temperature and luminosity of the star, although it never explicitly states a diameter (we are far more obsessed with this somewhat meaningless number than most scientists). Even the possible derived parameters in the paper allow for a huge range of possible diameters. This is unfortunate for a star that ended up at the top of Wikipedia's largest star list, but I can't find anything better out there. The S-B law is only approximate because of limb-darkening, other non-uniform disc luminosity features (sunspots are big news on a red supergiant), deviation from sphericity, and pulsations, but none of these problems affect the derived radius in any large or systematic way. Lithopsian (talk) 12:55, 29 June 2014 (UTC)[reply]

Lithopsian, thanks for the quick answer. unfortunately, your answer is a little bit unsatisfactory (no offense intended). 1. when you google NML Cygni, the 1650 R_☉ pop up basically on every site. but where does the 1650 come from? somebody must have come up with this number and it's not the scientists, who have written the paper, that has been quoted as reference for the 1650. 2. The luminosity and effective temperature define the size. yep, but within wiki I must adhere to https://en.wikipedia.org/wiki/Wikipedia:No_original_research. so i have to find a reference with the 1650 (or any other number) for NML Cygni, that i can use. anyway, thanks for your answer. I'll keep searching for the 1650 --Agentjoerg (talk) 14:10, 29 June 2014 (UTC)[reply]

You won't find that number. As I have explained, it is simply the radius corresponding to the published stellar parameters in that paper. It is not original research, it is a mathematical fact. It does seem though that you think someone has gone out with a ruler and measured the star. Far from it, that single number is a highly approximate value and could easily be double or half that value. Even if you could sit next to the star and measure it, the number is still meaningless since the star has the density of a helium balloon, tapering off in a wildly non-spherical atmosphere to an only slightly less dense shell of dust and gas larger than the solar system. Give up the search for an exact number, give up even the thought that an exact number has any meaning. I've edited the article to indicate a range of radii corresponding to possible physical parameters just from that single paper. Lithopsian (talk) 15:46, 29 June 2014 (UTC)[reply]

Here's a paper that actually quotes a radius, approximately 3,738 times the solar radius. Take that with a pinch of salt, but the number is in the paper (in cm!). No doubt you can find other numbers in other papers, for what that is worth.

http://iopscience.iop.org/0004-637X/610/1/427 Lithopsian (talk) 15:55, 29 June 2014 (UTC)[reply]

Lithopsian, thanks for the link. I'll use the 2,6 * 10E14cm. that's just good for me. see, where all this began, was, that i wanted to create NML Cygni in the german wiki, so i started to check the references in the english article. and i was quite puzzled, that i couldn't find the 1650, where they were supposed to be. i was taking the 1650 for a fact, because of the reference. fascinating, that the french, spanish, italian wiki all use the 1650 for the radius (and a lot of other sites in the net as well). congratulations, your calculated 1650 have left a heavy footprint in the net. that you think someone has gone out with a ruler and measured the star certainly not, i'm aware of the fact, that there's some uncertainty. see, for the star UY Scuti i've found the 1708 ± 192 in the quoted reference and that's fine, so i used it for the article. i'm aware that measuring the size (or the mass) of the stars isn't that easy and there are uncertainties. well, i've used up enough of your time. thanks for your answers and the link. i'll certainly use it. cheers --Agentjoerg (talk) 06:18, 30 June 2014 (UTC)[reply]

Check out the latest edit I made. I found a reasonable recent paper that puts an actual radius down in print. Not sure how I missed it before, maybe I need to spruce up my search techniques. The value is quite low at 1183 R_☉ (due to a temperature at the high end) which will no doubt disappoint some people. Lithopsian (talk) 16:43, 10 May 2016 (UTC)[reply]

@Lithopsian The 3.613 billion km/16.2 mas was also calculated by the Stefan-Boltzmann law, so how could you also calculate 1,650 R_☉ with the S-B law? @Agentjoerg Also, if you search up NML Cygni on Google, it now says 1,183 R_☉. ----Joey P. - THE OFFICIAL 03:38, 5 October 2017 (UTC)[reply]

1650 was probably poor rounding of a rather desperate calculation when there was no better source. Does it matter? That number isn't in the article now and it isn't going to be in the article. What you found on Google is irrelevant, it was only copied from Wikipedia and we all know that Wikipedia is not a reliable source ;) Which means 99% of the internet is not a reliable source! Lithopsian (talk) 11:02, 5 October 2017 (UTC)[reply]

Just to keep most people happy, I had to re-add 1,650 R_☉ (without removing 1,183 R_☉, 1,638.96 R_☉, and 2,769.84 R_☉.) Anyway, Wikipedia is usually incomplete, and is usually considered by most people to be contrary to popular belief, etc. ----Joey P. - THE OFFICIAL 02:12, 10 October 2017 (UTC)[reply]

We're not here to keep people happy. Lithopsian (talk) 10:46, 10 October 2017 (UTC)[reply]

The paper cites the photospheric measurement of the star as 22 mas. Given the distance of 5300 ly, this gives me 1,580 solar radii. Another paper gives 14 mas, giving 1,490 solar radii. Given luminosity of 300,000 L and temperature 3,300 K, this gives 1,750 solar radii. However, I was not consistent with my figures. I want to know exactly how the figure 1,650 solar radii was quoted. SkyFlubbler (talk) 22:37, 14 September 2014 (UTC)[reply]

The radius is not calculated from the angular radius. As explained in the paper, 16.2 mas is not a directly measured value. It was derived from assumed values of the temperature, luminosity, and distance. 1,650 is a rounded value for the most likely physical parameters given in the reference (3,250K and 270,000 L). This value was originally in this article and copied to the most luminous stars page. Now this article gives a range of radii from the possible physical parameters outlined in the most recent paper. It is unfortunate that a single highly approximate number caused one particular star to bubble up to the top of a list and then got quoted all over the internet as if it were carved in stone, but there you go. It will almost certainly change in a future paper, or another star will randomly bubble up to the top of the list, and people will blindly copy a different number onto all their blogs :( Lithopsian (talk) 10:52, 15 September 2014 (UTC)[reply]

Do you found any papers lately concerning the Rosseland radius of this star? When I've averaged the values in the paper, it gives 1,580-2,090 solar radii. Concerning the 3250K with luminosity of 270,000L, I've got a value as low as 1,450 solar radii. How do you got that value, anyway? I think my formula is wrong. SkyFlubbler (talk) 13:05, 17 September 2014 (UTC)[reply]

Don't you think that NML cygni's radius should be listed as 2212.5±562.5? Cause UY Scuti's is listed as 1708±192 and not 1516-1900. aaaaaaaaaaaaaaaaaaaaaa (talk) 01:28, 31 May 2015 (UTC)[reply]

Absolutely not. Nobody has ever published a (meaninglessly precise) number 2,212.5. 1,642 and 2,775 are two independent calculations without error ranges. We have no basis for averaging them or inventing a statistical error range, and even if we did have data for weighting them and performing statistical manipulation, that isn't Wikipedia's job. We're on shaky enough ground already deriving a radius from a luminosity and effective temperature. Lithopsian (talk) 11:44, 31 May 2015 (UTC)[reply]

@Lithopsian:@I am. furhan.:Please Lithopsian explain this absolutely appalling reverted edit here [1] The revert editor was a newbee, and this edit was questioned by aaaaaaaaaaaaaaaaaaaaaa, an all you can say is "We have no basis for averaging them or inventing a statistical error range, and even if we did have data for weighting them and performing statistical manipulation, that isn't Wikipedia's job." Says who? Most of this should be decided by collaboration or direct reference. All that is required is "Encyclopedic content must be verifiable." It says it a the top of this actual edit page!

Worse here, is that there is no reference (other than the text in the article), nor is it cited in the starbox. Anyone causally reading the starbox has no idea what "1,642 (– 2,775)(2,208.5?) R☉" actually means!!! (Please explain it before any future edits here!)

Lithopsian, do you understand what a "statistical error range" means. I.e. Planetary nebulae commonly use "statistical distances", and that is legitimately accepted even if it is ±50%. As long as the sources of the distances are quoted, it is perfectly to say some average value. If there are serious issues with some value or group of values, then just make a note at the end of the article – because it at least tells the casual reader and future editors what the hell is going on.

As for this earlier comment by Lithopsian[2] is absolute rubbish. Who says this? I.e. You say "It was derived from assumed values of the temperature, luminosity, and distance." Is this science or voodoo hocus pocus? Assumed how? The value is actually calculated R star (in solar units) = sqrt(Lstar / Lsun cor ⨉ Lsun / 4π ⨉ σ ⨉ T_eff⁴ / Rsun ) or Rsun =10^{(0.5 ⨉ log L + 2 ⨉ log ( 5870 / Teff )}, and assumes a black body. Rsun=696342 km. Lsun cor is the bolometric luminosity, and σ the Stefan-Boltzmann Constant c. 5.67x10^-8 W.m^-2.K^-4. The inputs, though error-some, are still found by actual observations. It is not a guess and nor is it without an error.

But of course the real basic reason the size is inaccurate is because the outer atmosphere is so tenuous that there is no way of knowing where the photosphere begins and ends. Evolution-wise this phase is very short on astronomical time scales, as superwinds blow the material back into interstellar space. In the end, readers of Wikipedia articles should be offered some way of comprehending the given information. That our job!

Lithopsian, showing complete disdain for other editors in trying to express that, then having it thrown back in their faces, as exampled above, is again unacceptable. Using your own personal theory and personal speculation to justify this is even worse. WP:GF is central to all editors here. All editors have the right to edit and challenge edits. You are responsible for you own edits - including reverts. Accept it, or please do something else.

(This time you cannot wrongly blame the use of similar tactics as you similarly use against me.) Arianewiki1 (talk) 11:38, 4 May 2016 (UTC)[reply]

(comment moved here from my talk page) Lithopsian (talk) 12:44, 17 May 2016 (UTC)[reply]
So if NML Cygni is 1183 solar radii, how come it isn't editted yet? Same for VX Sagittarii? (1350-1940) — Preceding unsigned comment added by 49.150.6.104 (talk) 13:46, 15 May 2016 (UTC)[reply]

I'm not really sure what you're asking, but I'll have a go at it. The article has been changed to reflect the most recent (explicitly) published value that I've been able to find for the radius of NML Cygni. I'm sorry if this doesn't match preconceived notions of how large the star might be, should be, or actually is. Wikipedia must be based on verifiable and reliable sources, and it is difficult to find a more verifiable and reliable source. There are older sources that are clearly rendered obsolete by newer research, and newer sources that don't explicitly state a radius. Previous numbers in this article were derived from the luminosity and effective temperature published in Zhang 2012, but that is perilously close to original research, and in any case Zhang doesn't opt for one particular value, only describing previous research re-normalised to a new distance. Maybe you can describe some of this in the text to make clear just how uncertain that size of the star is, not to mention that it is a pulsating variable that changes its size to a significant degree. Lithopsian (talk) 13:08, 17 May 2016 (UTC)[reply]

Niyet' has been editing size for NML Cygni to be 1650 R_☉, both in this article and in List of largest stars. I have reverted edits altering the size of NML Cygni from 1,183 to 1,650 R_☉ as the source cited, De beck, shows 1,183 R_☉. However the article is wrong according to the source for NML Cygni. Regards— User:Space Infinite 16:23, 22 May 2017 (UTC)[reply]

Turns out NML Cygni was never the largest star after all in 2012-2013, as I found the following information:

1,650 R☉ is NML Cyg's old size. The Zhang's reference says that size was 1,650 (-2,775) R☉ and the temperature (2,500–) 3,250 K and the De beck's reference says that the temperature is 3,834 K, If NML Cygni's temperature is 3,834 K, it means that NML Cygni's size is 1,183 R☉, If it is 2,500 K, its size would be 2,775 R☉ etc... because when the stars become warmer, they shrink, and cooler, they grow and the size of a giant, supergiant, hypergiant stars can change quickly. NML Cygni is listed as having a radius of 1,650 R☉ and being the largest star from 2012-2013. The NML Cygni article currently cites a size of 1,050 R☉ (it means that its temp is 4,074 K) from a 2010 paper. Clearly it wasn't the largest star in 2012 or 2013, It was WOH G64 (Not V838 Monocerotis because it was 380–1,570 R☉) with a size of 1,540-2,000 ^[1]R☉. And in general, when a range, use the small end of the range to sort, not the high end or some middle range and margin of error is not a range.

The 1,183 R☉ ref was made in 2010, so NML Cygni was only 1,183 R☉ all this time??????? I still use the old 1,650 R☉ for NML Cygni. So the 1,650, 2,208.5 and 2,775 for 2012 was never true. --Joey P. - THE OFFICIAL (talk) 05:19, 2 August 2017 (UTC)[reply]

We don't know the "true" size of any of these stars, and the margins of error in the values we do have are huge. Given that it is likely that the largest red supergiants are all a very similar size, the "largest known star" is likely to be the one which has the largest error in our current published values. For NML Cygni, two authors (de Beck and Zhang) have published slightly different data. Both are recent, but Zhang's is more recent and specifically about NML Cygni, with a new accurate distance. De Beck's paper is generic, calculating values for a wide selection of stars, and in other circumstances it would not be the preferred reference in the article. However, Zhang does not publish a actual radius so we would have to calculate it for ourselves which is less verifiable in Wikipedia terms. He doesn't even derive the temperature and luminosity, only adopted values from earlier (much older than de Beck) work, rescaled to the new distance. So we quote Zhang's distance and de Beck's physical properties. With a different approach we might just say that NML Cygni is somewhere between 1,183 R_☉ and 2,770 R_☉ (derived from 270,000 L_☉ and T_eff 2,500 K which even Zhang says is an unsatisfactory temperature) with similar very large ranges for other stars, which would be neither right nor wrong but very unclear. Which is why we don't have a timeline of which star was the biggest when. Remember, none of these stars changed size (that we know of), we just keep changing our guesses. Lithopsian (talk) 10:36, 2 August 2017 (UTC)[reply]

Also, I found these Portuguese videos that claim WOH G64 to be the largest star:

https://www.youtube.com/watch?v=aRf4JRyj2Ko https://www.youtube.com/watch?v=oOog-I9z0mQ — Preceding unsigned comment added by Joey P. - THE OFFICIAL (talk • contribs) 06:28, 8 September 2017 (UTC)[reply]

I could create a YouTube video and claim I was the largest star (might be fun to see how long before someone creates a Wikipedia article about me!), but it wouldn't be a very reliable source. The video creator might be a professional astronomer (or astronomical agency PR hack), but more likely it is some guy (or boy) in a basement who likes big stars and doesn't have a very robust approach to verifying the data. Or maybe just liked the name and went out searching for data to make it look like the largest star. Or it might even be a deliberate hoax - ever heard of fake news? Lithopsian (talk) 13:57, 8 September 2017 (UTC)[reply]

Good. I edited NML Cygni on the list of largest stars. — Preceding unsigned comment added by Joey P. - THE OFFICIAL (talk • contribs) 04:32, 3 August 2017 (UTC)[reply]

@Lithopsian maybe NML Cygni was the largest star in 2013 after all, but in reality it was 3.613 billion km and not 2.29 billion km. However, if that is true, it might still be the largest star. I think it would be best to leave it at 1,183 - 2,595 (~3,613,000,000/1,392,784) R_☉. ----Joey P. - THE OFFICIAL 03:44, 6 October 2017 (UTC)[reply]

The following Wikimedia Commons file used on this page has been nominated for deletion:

• Comparison of planets and stars (2017 update).png

Participate in the deletion discussion at the nomination page. Community Tech bot (talk) 07:51, 28 June 2018 (UTC)[reply]

Why is this star's visual magnitude so low? It's magnitude is 16.6 but it's only 1600 parsecs away? I calculated this star's absolute magnitude to be 5.58 which is even lower than our sun's (4.83). This is very low magnitude for any red supergiant star, let alone a red supergiant with a luminosity of over 200,000 L_☉. Is this star's magnitude so low because it's being blocked by surrounding dust because that would be a lot of surrounding dust.JayKayXD (talk) 02:57, 22 July 2019 (UTC)[reply]

Yes, it is heavily obscured by dust. There is something like four magnitudes of interstellar extinction, give or take. The rest if local dust from the star itself. It is effectively an infrared object, 10-15 magnitudes brighter in the K band than the V. It is also variable. Lithopsian (talk) 20:25, 22 July 2019 (UTC)[reply]

As NML Cygni has highly uncertain calculations about its luminosity, temperature, and radius, it was already removed from the list of largest stars.

As a result, the radius, temperature, and luminosity values had to be removed from the page until further measurements calculate it with more reliable certainty.

This's the same issue with stars like UY Scuti and Stephenson 2 DFK 1. Eric Nelson27 (talk) 08:57, 2 December 2023 (UTC)[reply]

I added the temperature and luminosity back (but not the size) because the luminosity and temperature listed before their removal was not related to the size estimate. Hope you understand. Atlantlc27Lol (talk) 21:21, 9 December 2023 (UTC)[reply]

Correct me if I’m wrong and maybe there’s been a change on the policy regarding the matter but is the way this radius was derived not simply a blatant violation of WP:Synthesis? Referencing two sources in Monnier et al. (2004) and Zhang et al. (2012) always seems like a no-go. Faren29 (talk) 15:09, 22 January 2026 (UTC)[reply]

Fairly blatant. Lithopsian (talk) 16:57, 22 January 2026 (UTC)[reply]

Thought as much, yet every single attempt to remove the value is reverted. When along the line was this deemed acceptable? You can never know the different assumptions in two separate papers and to my knowledge, Zhang et al. (2012) doesn’t even give an angular diameter. Faren29 (talk) 19:46, 24 January 2026 (UTC)[reply]

Has it ever been reverted? In this article, I mean; I know such things have been reverted elsewhere. I know I reverted one attempt by you to edit the radius, but that was not because of synthesis. Lithopsian (talk) 16:21, 25 January 2026 (UTC)[reply]

I believe the current radius was removed once or twice in the article and obviously a few times on the list, all being reverted. Your reversion of my edit I believe me incorrectly assuming the 1,639 and 2,770 solar radii values calculated from Zhang et al. (2012) was a range but it was actually one or the other because the paper doesn’t pick the temperature. De Beck et al. 2010 is probably still the best value for the star which is not saying much because we don’t have a lot to work with. Even if it is one star in a large table, it’s the only one that gives a direct radius. Faren29 (talk) 19:53, 25 January 2026 (UTC)[reply]

I have reverted many attempts to remove the calculated radius. The reason is that any simple calculations, within the scope of WP:CALC, are not original research, and since it is not OR, it is not SYNTHESIS. WP:NOTJUSTANYSYNTH explains this very well. Furthermore, in the absence of viable published radii that would overcome a calculated one, the only way is calculating one with two, mid-to-well measured values from different sources. 21 Andromedae (talk) 11:14, 26 January 2026 (UTC)[reply]

The problem is that this opens the floodgates to mix references in what you consider an acceptable circumstance. For example, V538 Carinae has a calculated distance 4,486 parsecs from Bailer-Jones et al. (2021) and a lim-darkened disc angular diameter of 3.542 mas from Cruzalebes et al. (2019). This comes to a radius of 1,709 solar radii. There’s not much else when it comes to stellar parameters on this star so would this be acceptable? Faren29 (talk) 13:35, 26 January 2026 (UTC)[reply]

Specific cases might be discussed individually, there are circumstances on whether a calculated radius would be justified or not. Just put the pros and cons in a balance. For NML Cygni itself, there does not seem to have any better alternative, radii in the literature are already rare and limited to old guesses, see Talk:List of largest stars/Archive 4#Remove NML Cyg? and Talk:List of largest stars/Archive 4#Calculated Radii for more information. Calculating a radius from two different sources is always a last resort and far from an ideal scenario, but is still better than nothing or suspicious guesstimates. For V538 Carinae itself, there is a published estimate here, so there is no need for a calculation. 21 Andromedae (talk) 19:44, 26 January 2026 (UTC)[reply]

NML Cygni has a published estimate, that being 1,183 solar radii from De Beck et al. (2010). Perhaps not optimal but we’re here to present what is verifiable, not necessarily true. Also to note, Healy et al. (2024) is a huge catalogue of stars using Gaia DR, so it is just as valid/invalid as De Beck et al (2010). Faren29 (talk) 03:59, 27 January 2026 (UTC)[reply]

De Beck et al. (2011) is not a reliable source. Along with relying on an inaccurate temperature and an outdated distance for NML Cyg, nearly all of their other radii are outliers, such as the bizarre 1,900 R_☉ for Betelgeuse, 1,342 R_☉ for IRC+10420, 737 R_☉ for Chi Cygni, 541 R_☉ for Mira A and 853 R_☉ for VX Sgr. I have removed it from lots of Wikipedia articles, and saying that Healy et al. (2024) is going to be 'as valid/invalid as De Beck et al (2010)' is a fairly simplistic assumption. It is better to use a more accurate calculation that IS verifiable (the calculation is shown, has references for the equation, angular diameter, and distance) rather than misinform the reader with a paper containing such bizarre estimates. Furthermore, WP:TRUTH is only an essay, not a policy or a guideline, and there are other essays (WP:Truth matters, WP:Verifiable but not false and WP:Editorial discretion) giving a counterpoint to it, at least in this context. 21 Andromedae (talk) 13:52, 29 January 2026 (UTC)[reply]

I found Mauron & Josselin (2010) table 6 suggests a value of 1,720 SR from a temperature of 3,310 K and a luminosity of 320,000 SL? Maybe could be something useful especially if it fits roughly into the >1,700 SR max value on the list currently? The distance given is also within the uncertainty of the current distance which is currently understood to be well-constrained. The temperature also matches for the spectral type. It’s maybe on the larger side but 1,350 SR estimate should be an absolute last resort. Monnier et al. (2004) notes the angular diameter given could be an underestimate so maybe a larger radius is possible. ~2026-99993-5 (talk) 21:24, 13 February 2026 (UTC)[reply]

The luminosity in this paper is much higher than the more accurate estimates (229,000 (2020) L_☉ and 270,000 (2012) L_☉), which will give a larger radius. Further, the effective temperature of the star is uncertain and hard to determine, and a radius calculated through Stefan-Boltzmann law is highly sensitive to the effective temperature. Mauron & Josselin took their estimate from van Loon et al. (2005), which on its own took it from a spectral type M6 III, but NML Cyg's spectral type is highly variable, M4.5–M7.9 Ia–III. I would not trust and include this estimate here, for the reasons above, and because it would also go to the list of largest stars, and there would be a lot of media mis-information about "the new largest star in 2026", which is not "new", neither the "largest star". That's why i am concerned over the accuracy of the radius estimates we cite in this article, or in articles for RSGs in general. There was a lot of mess in that list when accuracy was not considered the most important by their editors, Stephenson 2 DFK 1 is an example. And i disagree with you about calculating a radius with information from two different sources, i don't think it is a big deal. It is avoidable for most stars, but not here when there is no good published estimate. The Monnier ref says that their angular diameter should be considered an upper limit until more extensive data fully characterizes the “knee” or “break” in the visibility curve between circumstellar and photospheric emission, which could indicate the star is possibly smaller than 1,350 R_☉. At the cooler end of the spectral type (M7.9, the star could be larger), but this is uncertain too. Of course, there might be concessions, e.g. i would be okay with removing the error bars which are not calculated by the {{solar radius calculator}} template, but by hand, and are not actually disclosed and there is dispute on whether this is acceptable or not (e.g. this). 21 Andromedae (talk) 11:23, 12 March 2026 (UTC)[reply]

Angular diameter is an apparent quantity, while distance is an absolute quantity. Measuring the angular diameter does not require the distance to be known, or vice-versa. There will be no issue with combining both. 21 Andromedae (talk) 11:10, 26 January 2026 (UTC)[reply]

This is exactly why there is a policy forbidding this. We may think we know, we may think we know better than any of the published sources, we may even be correct, but unfortunately we are not WP:VERIFIABLE WP:RELIABLE sources. It isn't a case of whether we think there is an issue or not, it just isn't allowed. See WP:NOTTRUTH, for good or for bad. So far I haven't seen a single editor support your position that you should be able to do this because you are clever enough to know what is going on; it may be time to canvas a wider audience and see what people think. Lithopsian (talk) 15:39, 26 January 2026 (UTC)[reply]

There is no policy forbidding this calculation, but there is WP:CALC allowing it. The next sentence does not appear to have any relation to the scope of this discussion or my answer itself. Tell me where in my argument i suggest, even vaguely, that we know better than any of the published sources. My assertion that Angular diameter is an apparent quantity [...] There will be no issue with combining both is directly supported by Section 2 of both papers, where the materials and methods are addressed, showing that there is no assumption we are not aware of that would make the calculation invalid, such as in the case of calculating the radius using a luminosity of X L_☉ and an effective temperature Y, but the former rely on a bolometric correction that relies on a temperature Z that is different from temperature Y. The distance itself is measured using the surrounding astrophysical masers that are external to the stellar photosphere, while the angular diameter is directly obtained from the high-resolution inferterometric imaging of the star (and inevitably the nearby dust). The product of both angular diameter and distance will be inevitably the absolute size of the star, as per by the Lang (2006) reference. And for last, there is not even a single drop of my opinion here, just facts (WP:NOTJUSTANYSYNTH and WP:CALC) being presented, and others have indeed supported my assertion that such a calculation is not WP:SYNTH (e.g. Special:Diff/1322918515). 21 Andromedae (talk) 19:30, 26 January 2026 (UTC)[reply]