Talk:Stellar classification/Archive 2

Classification systems confusion
As a novice to astronomy I had a really difficult time understanding the differences between the classification systems discussed in the article (and referenced inconsistently):


 * Morgan - Keenan system
 * Harvard spectral classification
 * Yerkes classification (MKK sytem)
 * MK system (as named in the Yerkes classification paragraph)

Here's my current summarized understanding, so correct me if I'm wrong: the Morgan-Keenan system (aka MK system) combines the Harvard spectral classification system with a luminosity class to produce a two-dimensional classification. For example, a star classified "M2V" has spectral classification "M2" (two-tenths from M to L) and luminosity class V (meaning it is a dwarf star).

It took me a long time to get to this understanding from the current article. The problems I ran into, in no particular order:


 * At a high level, it is not at all clear which system is the current, state-of-the-art, standard.


 * Why is the paragraph which discusses the Morgan-Keenan system--the current standard system--titled the Yerkes Classification, a system which has been replaced???


 * From the paragraph on the Yerkes classification it is not at all clear that the Morgan-Keenan system uses the same spectral classifications as discussed in the Harvard spectral classification system above. The only hint of this comes from looking at the examples.


 * It is very confusing that the current classification system is buried underneath the paragraph on "conventional and apparent colors"--it makes it sound like the MK system is just another alternative, when in fact it is the current one.

The big fundamental problem I think is that this article discusses the history of classification systems interleaved with the description of the current classification system. I think it would make more sense to present Morgan-Keenan first, with both spectral and luminosity classes defined, and then have a later section discuss the history of the classification systems.

Anyway I don't want to rant since I'm obviously glad this page exists, I just think it could be easier to grok on the first couple reads. I'm happy to help out on anything, I just want to make sure I don't pollute the article with my own misunderstandings in the process. — Preceding unsigned comment added by Bpodgursky (talk • contribs) 10:06, 2 October 2013 (UTC)


 * Go for it. I've already rewritten the rambling and confused header so that it hopefully summarises the current usage of the spectral class without confusing and irrelevant detail.  Now the rest of the article should be reordered to match, with Secchi classes and such relegated to a historical background.  I suggest starting with the MKK system, bringing the separate "spectral types" section under it, and sending the older systems into a section that is clearly identified as historical. Lithopsian (talk) 11:12, 2 October 2013 (UTC)


 * Further, it seems that the sections on brown dwarf classes have got way out of hand, perhaps before there were separate articles for those stars. These should be brought back to brief summaries in line with other classes.  Should the section on habitability even be in this article?  Certainly not stuck in the middle like it is.  A whole section for magnetic stars which are just one of many peculiarities?  I don't know what to do with the section on apparent colours.  It is background information of marginal relevance, but given the big table comparing conventional and apparent colours within the Harvard classification system, it really needs to come earlier.  Lithopsian (talk) 11:12, 2 October 2013 (UTC)

Abundances
How abundant are the non-main-sequence stars (red giants, brown dwarfs, white dwarfs, neutron stars, etc.) relative to those on the main sequence? --JorisvS (talk) 09:30, 11 February 2014 (UTC)
 * The simple answer is "less abundant". There are quite a lot of white dwarfs, possibly 10% of all stars and rising due to their age and long lives.  Red giants are only around 1% of stars, and other classes even less abundant.  These numbers would be useful and informative.  Is this the best article for them? Lithopsian (talk) 12:31, 11 February 2014 (UTC)
 * I'd say yes, unless you know a more specialized article. --JorisvS (talk) 13:18, 11 February 2014 (UTC)
 * I agree. Some population statistics on the various classifications are entirely appropriate and should be included here. --Yaush (talk) 15:17, 11 February 2014 (UTC)

Harvard spectral classification
' ' I'm not a scientist, but in this sentence, which appears just below the table in "Harvard spectral classification", there are two adjective clauses, both beginning "in which":


 * "This stems from an early 20th-century model of stellar evolution in which stars were powered by gravitational contraction via the Kelvin–Helmholtz mechanism in which stars start their lives as very hot "early-type" stars, and then gradually cool down, thereby evolving into "late-type″ stars."

Maybe it's all right -- I don't know -- but this is not usually considered the best writing style. Perhaps someone who knows the subject can make an adjustment to the sentence. CorinneSD (talk) 20:07, 7 May 2014 (UTC)
 * Hi CorinneSD, I agree it's not the most readable of sentences, and I feel that it's the second in which (and what follows) that should possibility be changed. However, I have an engineering and scientific background and my wordsmithery is poor. If this was my own work I'd probably go with something more like :
 * "This stems from an early 20th-century model of stellar evolution in which stars were powered by gravitational contraction via the Kelvin–Helmholtz mechanism and as such started their lives as very hot "early-type" stars, and then gradually cooled down, thereby evolving into "late-type″ stars."
 * Cheers KylieTastic (talk) 22:22, 7 May 2014 (UTC)

7, 10, 12 or 13 classes?
"Most stars are currently classified under the Morgan–Keenan (MKK) system using the letters O, B, A, F, G, K, M, L, T and Y, a sequence from the hottest (O type) to the coolest (Y type). The types R and N are carbon-based stars, and the type S is zirconium-monoxide-based stars." At least 7 classes seems outdated (still the same classes just more): "Afterward, astronomy was left with the seven primary classes recognized today, in order: O, B, A, F, G, K, M." and my fix that could probably be improved. I'm not really into this. Annie Jump Cannon: "it is still being used for classification today" also "wrong"? As the classification has been extended (and might be again), can anyone fix these pages so they will not get out-of-date. [It seems right to credit her with the 7 class system but I notice that her name is no longer used, if it ever was.] comp.arch (talk) 11:16, 14 May 2014 (UTC) I'm not sure exactly what your question is. Are you looking for astronomy eyes to look over those two articles? Perhaps you're getting over-excited about the use of the extended classes such as L/T/Y and R/N. It is still entirely legitimate to consider the original sequence of seven letters as "primary". R/N describe somewhat uncommon, although quite visually bright, stars that are chemical variations of red giants that would otherwise be classified as M. Strictly these stars should be called C-R or C-N, variations on an original C class for carbon stars. There is also another chemical variant, the S class for Zirconium stars, as well as intermediates and further sub-classes. Not to mention other extensions to the classification such as for Wolf-Rayet and White Dwarf stars. None of them should be considered as part of any primary spectral sequence, with N perhaps being the closest as part of the original sequence beyond M. The L/T/Y classes are true cooler extensions to the sequence and they receive an amount of attention, including here on Wikipedia, that is little short of a publicity campaign. However, known examples are *extremely* rare. The true abundance of these small faint objects is likely to be higher than "extremely rare", but is not yet known. While the dividing line is still being argued about, at least some of these objects are not likely to even be considered stars. I'd be tempted to leave the articles as they were, referring to the original seven primary classes and not trying to specify all the myriad of modern extensions. Lithopsian (talk) 13:07, 14 May 2014 (UTC)

Useful source
https://books.google.com/books?id=S_Sh1i226wwC&pg=PA115&dq=spectral+type+stars&hl=en&sa=X&ei=koCjVJScEM-0oQTIwYGACw&ved=0CB8Q6AEwAA#v=onepage&q&f=false StringTheory11 (t • c) 04:58, 31 December 2014 (UTC)

Requested move 28 December 2014

 * The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review. No further edits should be made to this section. 

The result of the move request was: not moved. There were several subsequent proposals made during the course of the RM, and whilst there appears to be almost universal support for a move, it was never agreed upon the destination; Spectral classification of stars appeared to be a winner for a while, until Stellar spectral classification was suggested. It's not clear whether all the involved parties agreed to these, so it may be worth starting a new RM one of the two and pinging all the involved parties to gauge their support again. Number  5  7  17:21, 6 February 2015 (UTC)

Stellar classification → Spectral type – Stellar classification itself is a very broad topic that also includes classification such as variable star classification, binary star classification, and many other types of classification. This article only focuses (as it should, we have other articles for the others) on the Morgan–Keenan classification by temperature and luminosity (spectrum), and thus the title "stellar classification" is inappropriate, and should be made into a disambiguation page. StringTheory11 (t • c) 18:39, 28 December 2014 (UTC)
 * Updated target to spectral type per comments below. StringTheory11 (t • c) 03:24, 29 December 2014 (UTC)


 * Comment - It does seem to want to focus on the M-K system, but to my non-expert eyes appears to be an incoherent jumble of material. I can't really tell what is M-K and what might be some other system. If the article can be cleaned up to focus on M-K, then yes, the article should be moved. Rmember, we have a lot of infoboxes and articles that point to this specific title for explaining a given star's spectral class, so how those articles will be affected needs to be considered as well. — Huntster (t @ c) 20:20, 28 December 2014 (UTC)
 * Yes, this article really is in quite bad shape at the moment. I've done a little cleaning out the last few days to get rid of the worst of the problems, but there's still a lot more to do, especially with the first two sections. StringTheory11 (t • c) 20:55, 28 December 2014 (UTC)
 * Comment - The MK system isn't the only classification system, though it is the dominant system. I think a more appropriate title would be "spectral classification". Cheers, AstroCog (talk) 23:50, 28 December 2014 (UTC)
 * I'd be fine with that, or the even shorter "spectral type". StringTheory11 (t • c) 00:47, 29 December 2014 (UTC)
 * I'm good with "spectral type." Both MK and the preceding Harvard systems, which are closely related, should be covered. I don't think MK warrants a separate article by itself. --Yaush (talk) 00:56, 29 December 2014 (UTC)
 * Well, if MK doesn't need its own article, should things simply stay at this page, simply with better organisation? — Huntster (t @ c) 01:19, 29 December 2014 (UTC)
 * Note: due to above comments, I have changed the target of the RM to spectral type. Since no votes have been cast yet, I don't think this should cause any problems. StringTheory11 (t • c) 03:24, 29 December 2014 (UTC)
 * Support. --Yaush (talk) 04:44, 29 December 2014 (UTC)


 * Comment is this article going to be expanded to cover spectral classification of non-stellar objects? If not, then the proposed title has the same problem as the current one, being too broad. Spetral types of stars ? Stellar spectral types ? -- 65.94.40.137 (talk) 05:36, 29 December 2014 (UTC)
 * What if it was renamed Spectral classification of stars? Then it would be specific enough for the main topic. I could see a "top level" article called Classification of stars, covering many different ways of classifying, not just spectral classification. Cheers, AstroCog (talk) 14:13, 29 December 2014 (UTC)
 * I like that better. --Yaush (talk) 17:28, 29 December 2014 (UTC)
 * Spectral classification of stars sounds good to me. -- 65.94.40.137 (talk) 05:19, 30 December 2014 (UTC)
 * I'd be fine with Spectral classification of stars. I think the broader page Classification of stars should be a disambiguation page, though, directing readers to stuff like spectral classification, variable star classification, multiple star classification, etc. StringTheory11 (t • c) 18:01, 30 December 2014 (UTC)
 * Good idea. Cheers, AstroCog (talk) 02:47, 31 December 2014 (UTC)


 * Comment: IP 65.94 raises a good point. Is the end-game for this article to remain a broad coverage of stellar classifications, or will it focus on HK classifications? If the former, then why rename at all? Keep at "Stellar classification". If the latter, then it should be moved to the previously proposed Morgan–Keenan spectral classification or Morgan–Keenan stellar classification. I don't think I could support a move to "Spectral type". — Huntster (t @ c) 05:52, 29 December 2014 (UTC)


 * The title is either spectral class or spectral type, with the modern adoption being spectral type.


 * It is defined as; "A classification assigned to a star according the appearance of its spectrum."


 * Also; Spectral type is based on a temperature sequence, which has attached a luminosity class. I.e. I to VII.


 * Spectral Classification : Reference Examples


 * Buscombe, "MK Spectral Classification", 10th Catalog, 1992.
 * Keenan, “Spectral Classification,” in Basic Astronomical Data, ed. K. Strand.
 * IAU Symposium No. 50, was "Spectral Classification" (1973)


 * However, where this term used here is from The IAU Commission 45 is entitled "Stellar Classification", now under the Division G Commission 45 as Stellar Classification


 * Reading the 'Description' defines what Stellar Classification means. I.e. http://www.iau.org/science/scientific_bodies/divisions/G/


 * The article is mostly on Spectral Type, so this is what it should be called.


 * Sections
 * 5 Stellar classification, habitability, and the search for life
 * 6 Variable star classification
 * 7 Photometric classification


 * Are mostly separate subjects, which is under the broader topic of Stellar Classification, and this should be in a separate section.


 * I think the wording on the Section Conventional and apparent colors is seeming irrelevant to the subject of spectral type, excepting the statement colour is related to stellar surface temperature. Arianewiki1 (talk) 06:25, 29 December 2014 (UTC)


 * 75% support— The main sentence itself says: "Stellar classification is the classification of stars based on their spectral characteristics." But for me, I agree that the sentence is too broad. It must be spectral classification, as if we classify stars by type, that may be variable stars, giants, supergiants, neutron stars, etc. For me, the title spectral type is too narrow. That's what I got so far. However, can someone explain it further? SkyFlubbler (talk with me :-D) 09:01, 29 December 2014 (UTC)

Do we have a consensus on "Spectral classification of stars"? --Yaush (talk) 18:11, 1 January 2015 (UTC)


 * I'd agree., except Stellar Spectral Classification is much better.Arianewiki1 (talk) 18:43, 3 January 2015 (UTC)
 * Why? --Yaush (talk) 22:01, 3 January 2015 (UTC)
 * Stellar spectral classification is shorter, and probably is more likely to be typed into the search bar. I'd personally be fine with pretty much anything that mentions "spectral". StringTheory11 (t • c) 01:56, 5 January 2015 (UTC)
 * Stellar spectral classification is fine by me -- 65.94.40.137 (talk) 04:08, 5 January 2015 (UTC)

Comment, since this is a rather important article and the renaming could have a significant impact on the project, I think this should remain open for longer than usual, maybe two weeks instead of the usual one, to get as many opinions as possible. Thoughts? StringTheory11 (t • c) 02:07, 5 January 2015 (UTC)


 * Comment 'Stellar classification' is an appropriate title for an article, so that needs to be retained in some form. I'd suggest improving the article first, then splitting off 'Spectral Type' if that topic meets the criteria for an article split. Praemonitus (talk) 03:02, 16 January 2015 (UTC)


 * The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page or in a move review. No further edits should be made to this section.

Why O, B, A, F, G, K, and M?
What is the reason for those particular 7 letters? What does each letter stand for? 70.109.155.240 (talk) 04:41, 27 February 2015 (UTC)
 * The article already explains the history behind these letters. Lithopsian (talk) 10:15, 27 February 2015 (UTC)
 * It does, though it is not particularly complete. It says that "Annie Jump Cannon returned to the lettered types, but dropped all letters except O, B, A, F, G, K, and M", but does not explain why she did so. --JorisvS (talk) 10:40, 27 February 2015 (UTC)
 * The paper is referenced, but she never explains why those letters. I suspect it is just an oversight.  The HD catalogue used 15 letters, but it provided a quick reference described as "specimens of a number of these classes of spectra" which coincidentally were A, B, F, G, K, and M.  O is an entirely separate type of spectrum representing Secchi class V, so had to be included.  Draper class N corresponds to Secchi class IV, but was explicitly ignored because there were no examples found.  That's just my theory though, the paper itself just describes the included letters with no mention of why other letters were ignored.  Lithopsian (talk) 11:50, 27 February 2015 (UTC)

Inconsistent mass?
The upper bound for mass of M spectral type, shown here as 0.45 solar mass, is not consistent with the mass provided in red dwarf, shown instead as 0.6 solar mass. Why is that? I didn't check this for other pages, but there might also be similar inconsistent information. Ingebot (talk) 09:08, 18 November 2015 (UTC)
 * Stars form a continuum, not necessarily falling neatly into distinct boxes invented by humans. The Red dwarf article specifically mentions, in the opening sentence no less, that the category it includes both M and some K stars (although it then contradicts itself by listing only M stars in a table of red dwarf properties).  The masses of stars of a particular type are not exact, and certainly not known precisely, and will also cover a range even when known precisely.  For example, the binary ADS 7251 consists of M0 and K7 components, with the M0 star both brighter and more massive.  Still, the 0.45 value seems slightly low to me, 0.6 being closer to what I'd expect.  Feel free to hunt down some references more recent than the 1981 paper quoted in this article.  Lithopsian (talk) 11:33, 18 November 2015 (UTC)

Young lithium-rich giant star
KIC 9821622: An interesting lithium-rich giant in the Kepler field, For future note. Thanks, Marasama (talk) 14:47, 21 December 2015 (UTC)

Authority Control request on 26 December 2015
? — 73.47.37.131 (talk) 23:53, 26 December 2015 (UTC)


 * This is not a valid request. Please state exactly what it is you want added to the article rather than having others guess. — Huntster (t @ c) 01:02, 27 December 2015 (UTC)

What happened to R & N ?
I learnt the list as OBAFGKMRNS. The article mentions S but what happened to R and N? Somewhere I read that RNS were later additions describing stars with heavy metals to the original OBAFGKM list.150.227.15.253 (talk) 13:02, 12 February 2016 (UTC)
 * Wow, you must be even older than me! You're talking ancient history here.  R and N essentially still exist, as C-R and C-N within the carbon star classification system.  R and N were largely dropped in the 1960's although some authors persisted with them for much longer.  The C class wasn't expanded into C-H, C-N, and C-R until 1993 I think.  For that period the C class didn't include a good mapping of the R and N classes, which is one reason some people kept using them.  Lithopsian (talk) 14:44, 12 February 2016 (UTC)

Semi-protected edit request on 15 March 2019
'Harvard spectral classification' section: 'Class' table> 'Fraction of all main-sequence stars' column:
 * change "~0.00003%" to "~3.034*10^-5%"

....CRITICAL-ERROR →  change "0.13%" to "~0.1214%"
 * change "0.6%" to "~0.6068%"
 * change "3%" to "~3.034%"
 * change "7.6%" to "~7.646%"
 * change "12.1%" to "~12.14%"

....CRITICAL-ERROR →  change "76.45%" to "~76.46%"

HassoonBobster (talk) 21:10, 15 March 2019 (UTC)
 * All changes to be made to 4 significant figures for standard mathematical consistency
 * Tilde(~) used before all numbers since they are all approximated to 4 s.f.
 * just pointing out that the editors have made calculation error from their source (refer pg 33 last table)


 * I will be happy to make any necessary changes, but I think you need to show a little more of your working because I don't get the same results that you show when I do the calculations myself. I do see some dodgy rounding in the article numbers, and some of the numbers do appear to be incorrect but not as you show them.  Also, why four significant figures?  The input data is two significant figures at best.  Consistency is good, but meaningless precision is not.  I don't think the tildes are going to happen.  All figures are approximate, and there is nothing special about these that requires tagging them as especially approximate.  Tildes are generally only used in astronomy for really really approximate values, preferably when used in the citation itself.  Lithopsian (talk) 21:46, 15 March 2019 (UTC)

What happened to R & N ?
I learnt the list as OBAFGKMRNS. The article mentions S but what happened to R and N? Somewhere I read that RNS were later additions describing stars with heavy metals to the original OBAFGKM list.150.227.15.253 (talk) 13:02, 12 February 2016 (UTC)
 * Wow, you must be even older than me! You're talking ancient history here.  R and N essentially still exist, as C-R and C-N within the carbon star classification system.  R and N were largely dropped in the 1960's although some authors persisted with them for much longer.  The C class wasn't expanded into C-H, C-N, and C-R until 1993 I think.  For that period the C class didn't include a good mapping of the R and N classes, which is one reason some people kept using them.  Lithopsian (talk) 14:44, 12 February 2016 (UTC)

Semi-protected edit request on 15 March 2019
'Harvard spectral classification' section: 'Class' table> 'Fraction of all main-sequence stars' column:
 * change "~0.00003%" to "~3.034*10^-5%"

....CRITICAL-ERROR →  change "0.13%" to "~0.1214%"
 * change "0.6%" to "~0.6068%"
 * change "3%" to "~3.034%"
 * change "7.6%" to "~7.646%"
 * change "12.1%" to "~12.14%"

....CRITICAL-ERROR →  change "76.45%" to "~76.46%"

HassoonBobster (talk) 21:10, 15 March 2019 (UTC)
 * All changes to be made to 4 significant figures for standard mathematical consistency
 * Tilde(~) used before all numbers since they are all approximated to 4 s.f.
 * just pointing out that the editors have made calculation error from their source (refer pg 33 last table)


 * I will be happy to make any necessary changes, but I think you need to show a little more of your working because I don't get the same results that you show when I do the calculations myself. I do see some dodgy rounding in the article numbers, and some of the numbers do appear to be incorrect but not as you show them.  Also, why four significant figures?  The input data is two significant figures at best.  Consistency is good, but meaningless precision is not.  I don't think the tildes are going to happen.  All figures are approximate, and there is nothing special about these that requires tagging them as especially approximate.  Tildes are generally only used in astronomy for really really approximate values, preferably when used in the citation itself.  Lithopsian (talk) 21:46, 15 March 2019 (UTC)

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Canopus listed as an F-type supergiant
On the section for Class F, Canopus is listed on the right as a Class F supergiant, isn't it really a class A?
 * The spectrum of Canopus has traditionally been classified as F0 Iab or something similar. In 1989, a refinement of the traditional methods for determining the luminosity classes of "early F-type stars" resulted in the subtly different spectral type of A9II.  This is now accepted as a better type although you'll still often see the old one.  Lithopsian (talk) 16:52, 22 December 2020 (UTC)