Talk:Main sequence/Archive 1

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Temperatures in table

What part of the star do the temperatures in this table refer to? Surface? Core? Could someone with the appropriate knowledge alter this for clarity? QmunkE 15:47, 10 March 2006 (UTC)

All the temperatures refer to surface temp. Any text-book with the Hertzprung-Russel diagram will tell you that!

Bet you find this Interesting?

I had a thought the other day. And tried to find this answer to this on Wikipedia and other sources. But as a complete layman became very confused, parsecs/light years ect. This is my thought, we (the human race) have been sending out RF signals of a reasonable strength since 1922, please correct me on this if I have this wrong. Based on this knowledge, I wondered how far and how many star like suns (G class stars) have these RF signals reached by this year, 2007 ? You know where I'm going with this thought, and yes maybe life is not restricted to G class stars, or maybe it is, or maybe only to G2V, and we all known G2V's are capable! Then there's the age of these stars, and then the metallic make up as well. I wish someone with the right knowledge would draw up a list of theses stars. And using the above knowledge. We could then break the list up into the most lightly to the most unlikely places that intelligent life may exist. And that have also received RF signals from us. I believe this list would be helpful to SETI, to reduce their listing down to size, so they can focus on a more broader range of RF signals. As I also believe the RF's they are searching are far too narrow, and I feel a lot of time and money is going to waist at SETI. If anyone can help me with this please do, maybe I've got this wrong as I'm just a layman. But in any case, post me something, its bugging me!

The brief answer... According to [1], there are 133 sun-like stars withing 50 light years. Astronaut 01:20, 15 July 2007 (UTC)
The longer (POV) answer... It's my opinion that planets are possible round most stars, and with over 100 billion stars in the milky way galaxy alone that makes a hell of a lot of planets. Probably most are not capable of supporting "life as we know it" because they are too cold, too hot, too young, or in weird orbits round multiple stars, etc; but if even a tiny proportion of 1% of billions of planets were capable of life, there are still many places to look. For Earth's radio/TV transmissions to have reached an extraterrestial civilization and for them to have recognised it and replied to us, they would have to be no more than about 50 light years away for us to be detecting their reply now. Even so, restricting the search to such possible replies, leaves perhaps hundreds of potential targets for SETI.
But, if you also consider that if, say, an extraterrestial civilization started experimenting with radio 500 years ago, their signals would now be detectable from 500 light years away, then SETI needs to consider this possibility as well.
I think SETI have deliberately set out their search to cover most if not all nearby stars, and a select list of more distant stars.
Astronaut 01:53, 15 July 2007 (UTC)

Source of Main Sequence Data?

What is the source of the "Main Sequence Data" table that contains the stellar class, radius, luminosity, and temperature? I've never seen a table like that, and it's very useful for figuring out what specific stars are like. Does it come from the Encyclopedia of Astronomy and Astrophysics?

Raddick 17:50, 25 July 2007 (UTC)


Major revision

Hi Bob. The article on the main sequence is in need of fixing up. You have done such a great job on other astronomy pages, do you have time for that one? I can't spend much time on it, but am happy to pitch in or offer advice if needed. Timb66 10:21, 1 December 2007 (UTC)

Hi. Thank you for the suggestion. Yes I can try to expand it. — RJH (talk) 17:48, 2 December 2007 (UTC)
Okay I have expanded it. There's still some references needed and I'll work on that. When you have a moment, could you look through it and see what needs expanding, clarifying or even removing? I'm sure there may be some corrections needed and a bit of fine tuning. Thank you. — RJH (talk) 18:46, 6 December 2007 (UTC)

Hi Bob. Many thanks for a great and thorough job. I haven't had time to read carefully yet, but my first impression is that some of this might be better in the main article on the Hertzsprung-Russell_diagram. What do you think? Timb66 (talk) 05:34, 7 December 2007 (UTC)

Yes it may be that the two articles could be merged. What parts did you have in mind?
In some places I included content I thought necessary for explanation of information related to the main sequence. These, of course, discussed topics related to the HR diagram as a whole. There are probably a few areas that could be pruned, such as mention of the triple alpha process. But if it is to remain a separate article, I thought it needs to at least briefly explain both pre- and post-main sequence. — RJH (talk) 16:36, 7 December 2007 (UTC)

GA review—on hold

The article basicly satisfies GA criteria. However there are some errors that should be fixed.

1) In the fourth paragraphs in 'History' there is a sentence "Russell proposed that the giant stars must have a lower density or higher surface-brightness than dwarfs". What does "higher surface brighteness" means. The brightnees is determened by the temperature, is not it? And the temperature is similar for both red dwarfs and red giants.

The source article from Russell states that the "giant stars must have low density or great surface-brightness, and the reverse is true of dwarf stars". I'll use a quotation.

2) The last paragraph in the 'History' and the last paragraph in 'Characteristics' duplicate each other and should be merged. In addition the paragraph in 'Characteristics' lacks any citations.

Merged the common content.

3) Please, change bold font to the normal. I mean "zero age main sequence", or ZAMS in 'Formation' and main sequence in the caption of the last figure.

Fixed.

4) 'Cross-section of a Sun-like star, showing the different regions.'— there should be no period at the end of this caption.

Fixed.

5) In the 'Evolutionary tracks' there is a sentence "For intermediate-mass stars of more than 2 solar masses, the core can reach a temperature where it becomes hot enough to burn helium into carbon via the triple alpha process.". This implies that the Sun will never burn helium, which is wrong. The lower limit for the stars to burn helium is around 0.65 solar masses, which is enough to form a helium core of 0.45 solar masses.

Fixed w/ references.

6) The second paragraph from the end in 'Lifetime' is unreferenced.

References added.

7) The Vega may be a bad example of A0 star (in the table). It looks hot only because we look at its pole. It real mass is 2.1 solar masses, which is similar to β Pictoris. Its average spectral class is probably A3-A4 and luminosity is 37 solar (remember Vega article).

I changed the example.

Ruslik (talk) 19:31, 7 January 2008 (UTC)

Thanks.—RJH (talk) 17:04, 8 January 2008 (UTC)

I will promote the article, but 0.5 solar masses value is an underestimate. They seem to forget about large mass loss during RGB phase. I think this point deserves further research. Ruslik (talk) 17:54, 8 January 2008 (UTC)

The various sources I checked seem to be all over the map with regards to the minimum solar masses for triple-alpha fusion:
The article http://arxiv.org/abs/astro-ph/9509062 does give a value of 0.6 for stars to subsequently follow the AGB. Thanks.—RJH (talk) 21:02, 8 January 2008 (UTC)

Contradictory information

The Main sequence and the Luminosity articles give contradictory information about luminosity being proportional to a power of stelar mass. The Main Sequence article mentions M^3.5 while the luminosity article mentions M^3.9. Could someone correct this? -Paul- (talk) 01:28, 9 February 2008 (UTC)

Both numbers are approximations within a range. Depending on where on the main sequence you are (the high-mass end versus the low-mass end) the mass-luminosity relation has a modestly different slope. BSVulturis (talk) 22:14, 5 December 2008 (UTC)

Va vs. Vb

This is a new one to me. Can someone explain the difference between a main-sequence 'a' and main-sequence 'b' star? The classification system gets finer and finer! Is the Sun a G2Va or G2Vb star? 68Kustom (talk) 10:21, 10 February 2008 (UTC)

Supergiants can be Ia or Ib. Perhaps that is what you mean? I haven't seen a stellar classification Va or Vb. Do you have an example?—RJH (talk) 22:18, 12 February 2008 (UTC)
Found 'em: http://en.wikipedia.org/wiki/85_Pegasi Lists 85 as a G5Vb. http://en.wikipedia.org/wiki/51_Pegasi. The clincher: http://en.wikipedia.org/wiki/Stellar_classification (scroll to the Yerkes classification info). 68Kustom (talk) 02:31, 17 February 2008 (UTC)
Ah, okay. I think the suffix may be from Spectral class#Spectral peculiarities (although that table doesn't look complete). The "b" would be for a spectroscopic binary, but I'm not sure about the "a". SIMBAD gives a classification of G2V+ for 51 Peg.[2] As for the stellar classification page, the Va and Vb don't seem to be mentioned on the Morgan & Keenan paper cited,[3] so I'm a little skeptical about that table.
I'm not sure that it would be beneficial for this article to get in to the messy details of peculiar spectra. We've already got a peculiar star page. Thanks.—RJH (talk) 17:53, 17 February 2008 (UTC)
I thought too that somebody might have been a bit too organized in assigning 'a' and 'b' to main sequence stars. Perhaps the mixup is over something like Alpha Cen A and B? In terms of supergiants, though, what's the difference between Ia and Ib? 68Kustom (talk) 23:29, 17 February 2008 (UTC)
The Ia-0/Ia/Iab/Ib sub-categories just seem to be a difference in supergiant luminosity.—RJH (talk) 19:57, 28 February 2008 (UTC)

Power Laws

What do people feel about a new section discussing the approximate power law relationships on the Main Sequence, and how they are derived? Luminosity-temp, Temp-Mass, Luminosity-Mass, and Stellar lifetime-Mass relationships could all be included for low, medium, and high mass main sequence stars. Density, radius, and other variables may also be included in their own scalings if wanted.... I'm not an expert so I wouldn't feel comfortable writing it up accurately, although if someone has the requisite background, I think it could be very useful.... —Preceding unsigned comment added by Firth m (talk • contribs) 17:23, 28 February 2008 (UTC)

Would it be of interest to the readership? If it tells a reader something more than just a set of derived empirical relationships then it could be useful. But it would need to be properly referenced.—RJH (talk) 19:51, 28 February 2008 (UTC)

Need to include following topics

Don't have time to write these but... Need to

1) Effect of age and composition on stars - in particular the fact that population I stars have different MS curves than population III stars, and

2) The role of Main sequence in cosmic distance ladder.

Roadrunner (talk) 05:18, 31 March 2009 (UTC)

Thanks for the suggestions. But it is possible the second may be better covered on the linked page rather than here.—RJH (talk) 18:52, 31 March 2009 (UTC)


What I came to this page looking for is some clue of how an individual star transits the HR diagram over the course of it's lifetime. I.E. consider a star that is at point (x,y) on the HR diagram during the main part of its lifetime, and then as the article states... "At this point the star is evolving off the main sequence and entering the giant branch" What will that star's giant point (x',y') be? The answers could go here or in the Stellar Evolution page. There's a diagram at the Stellar Evolution page, but it's kinda childishly conceptual. I'd be especially happy to see a curve that looks like a Carnot diagram - except non-adiabatic of course! --MathInclined (talk) 02:27, 13 June 2011 (UTC)

The stellar evolution article is probably the better place for it. Regards, RJH (talk) 15:09, 13 June 2011 (UTC)

Up and to the right?

In the "Formation" section it says "On the HR diagram, the evolving star moves up and to the right of the main sequence" but anything moving up the chart moves to the left , not the right. Johnor (talk) 00:02, 1 April 2009 (UTC)

Oh duh! I guess it means "up" in terms of higher numbers which is really "down" visually. Never mind.Johnor (talk) 00:07, 1 April 2009 (UTC)
  • You bring up an important point. The star stays at a single place on the diagram for most of its history, then, when it reaches its supergiant stage, it moves up and to the right. If this were a map, it would move northeast. The main sequence is not a path that a star starts on at the lower right and goes all the way up to the upper left. I think the article would be clearer if it had a diagram of the path of a single star of a certain type - or maybe several such diagrams for stars of different types. --Cbdorsett (talk) 04:07, 1 April 2009 (UTC)
The confusion seems to arise from the word "sequence", which in common arlance usually connotes a progression over time. Ronstew (talk) 16:43, 1 April 2009 (UTC)

Relationship to Cosmology and Astrometry

I'm moving this completely unsourced material here until it can be brought in line with FA criteria.

The existence of the turnoff also has implications for cosmology. The expected lifetime of red dwarfs on the main sequence has been calculated by computer models to be in the tens of billions of years. The observed fact that there are no known examples of red dwarfs that have moved off the main sequence has been taken as evidence that the universe has a finite lifetime, and the maximum age of observed globular clusters gives a minimum age for the universe.
Main sequence stars are also useful in establishing distances to stars and for creating a cosmic distance ladder. Because there is a definite relationship between temperature and luminosity, a main sequence star can be used as a standard candle, and once its spectrum is observed, its brightness and hence distance can be calculated.

Sorry.—RJH (talk) 22:51, 4 April 2009 (UTC)

Questions for Simple English WP

Hi Folks,

I intend to create the Main Sequence article in the Simple English Wikipedia. (Think of the SEWP as an online students' or childrens' encyclopedia.) To do so, I have some questions. Please bear in mind that I'm a layman when it comes to astronomy.

I'll try to answer your questions.—RJH (talk) 15:57, 11 August 2009 (UTC)
  • What is the importance of the main sequence?
    • Does it contain most of the stars? (If so, how do you define "most"? The enWP article says "The majority of stars on a typical HR diagram lie along the main sequence curve". Do you define "majority" as simply greater than 50%? What is an untypical HR diagram.)
      • In this context, 'most' would be about 90% of active stars. I.e. those still engaged in nuclear fusion. The reason for this is because helium and other elements generate less energy (per unit mass) than hydrogen, so evolved stars burn through that non-hydrogen fuel about ten times as fast. (See the "Lifetime" section.)
      • You can build an HR diagram based on any group of stars. Thus an old globular cluster will have a more evolved population than the solar neighborhood and the HR diagram will look different.
    • Do main sequence stars follow a difference life-cycle than other stars? (Are there "other stars"? See question #3 below.)
      • I believe that all stars composed of normal matter will pass through the main sequence. At least I'm not aware of any exceptions.
    • What was the importance of the main sequence in the past, if it differs significantly from the present?
      • As stars die and eject their outer envelopes, the material that is being used to build stars is gradually being enriched by elements heavier than helium. Stars rich in heavier elements will follow slightly different tracks across the HR diagram.
    • What would you say are the two or three main things that make the main sequence important.
      • It is useful, for example, as a distance indicator to a population of stars (such as a galaxy) and as a means to determine the age of a cluster. The position on the sequence pretty much determines how long the star will remain on the sequence.
  • How do you determine if a star is a main sequence star?
    This is, at least conceptually, different than determining if a star is on the main sequence. That's simple (in theory) but, as you go up the cosmic distance ladder, things get diceyer. Do you have to plot thousands of stars from (say) a particular globular cluster to determine that that globular cluster even has a main sequence? How about stars in distant superclusters or in the Sloan Great Wall? Do those have main sequence stars? How do you know?
    • A main sequence star is still burning hydrogen at it's core. But otherwise, I believe you can tell based on the star's spectrum. As a star evolves away from the main sequence, the spectra will change somewhat. See Stellar classification. The main sequence exists because of the way that a star functions internally. If the physics operates the same in other parts of the universe and the stars are composed of the same materials, then the expectation would be that they operate the same as here and therefore follow the same evolutionary tracks. The one area where there might be an issue is with population III stars in the early universe. They were very massive stars; I think possibly more massive than stars that can form today. Did they lie along an extended main sequence? I don't know.
  • Do all stars, without exception, form from protostars on the main sequence?
    • Just about. A few stars are formed by mergers of other stars. See, for example, blue stragglers. I suppose an outlandish possibility would be a non-stellar object in a close orbit could accrete enough matter to become a star, but I don't recall seeing anything written up on that possibility so I wouldn't bother mentioning it. Shrug.
  • The enWP article on the Hertzsprung–Russell diagram says (in the last sentence) that HRD's aren't used any more for developing new theories. Is that also true about the main sequence?
    • I have no idea whether that is true, and in fact I'd be a little skeptical of it unless there is a proper cite.
  • The article talks a lot about the main sequence and the Hertzsprung–Russell diagram. Is there only one Hertzsprung–Russell diagram? If so, which one? If there are many H-R diagrams, aren't there also many main sequences? How do I explain that to children?
  • What facts would you include in an article on the main sequence intended mostly for children and other students?
    • Oh I guess I'd focus on the relationship between stellar mass, temperature and lifetime. I'd also explain how the star generates it's energy, and why this is relevant to the main sequence.

As we say in SEWP, "You shouldn't lie to children". Children will accept whatever's in books as if it were gospel, especially for An Encyclopedia. Grown-ups know that when a reference book says A is B you have to treat that statement with a grain of salt (unless the article happens to be on mathematics, law or computer programming :-); children do not. Everything you say to them is either black or white. Therefore, we must be careful in our articles to be exact: to say what is true and, when adults do not know the truth precisely, to say that as well.

I'm sure you're right.

I could sprinkle my article with a lot of "Scientists say that..." and "according to most professional astrononers, ..." but that's weaseling. I prefer to say something like, for example, "About nine out of ten (or 999 out of 1000 or whatever) stars in the Milky Way were formed on the main sequence from protostars. (Of course, when we say 'on the main sequence' we really mean: having a brightness and a temperature that causes them to be plotted within the main sequence region on a Hertzsprung-Russell diagram.)"

That is covered by WP guidelines, I believe.

I know my questions may seem babyish to you but I like to get my facts straight before I write about them in SEWP. Also, I would appreciate it if someone could look at the Simple English article Hertzsprung-Russell Diagram. Any comments are welcome.

Thanks a lot. --RoyGoldsmith (talk) 11:16, 11 August 2009 (UTC)

Good luck.—RJH (talk) 15:57, 11 August 2009 (UTC)
Thank you so much for getting me started. You didn't answer everything but I can figure it out by myself now. My basic problem was that I didn't know how much reliability to read into various declarative statements about the main sequence (and stars in general). Now I think I do.
One unrelated question on the subject of...well I'd guess you'd call it the philosophy of science. What would you say is the chance that all our theories about stellar evolution are just plain wrong? (Or significantly wrong.) No, I'm not a creationist; I make my living as an engineer. I agree that scientific theories are the best explanations we have now. And, presumably, when something better comes along, we'll change them.
I don't think I could even estimate the odds of something like that, and I try to avoid saying that what science comes up with is the absolute truth. But the current models seem to produce a pretty good match with what astronomers are observing, and they are consistent with current physics theory. Models are always evolving, of course, but the fundamentals like nuclear fusion, thermodynamics, &c., are probably pretty well established. On the other hand, the whole topic of stellar magnetic fields seems highly complex, at least to me, and I'm still reading articles on new discoveries related to stellar activity. So it wouldn't be a surprise to see ideas emerging in that subject area. (Which is very cool, of course.)
It's just that cosmology and the cosmic distance ladder have always struck me as a sort of white swan science. Especially since the observations are so far away. As you say in your answer to question #2, "If the physics operates the same in other parts of the universe..." Another way of asking my question would be: What would you say is the chance that physics is proven different in other parts of the universe, sometime in the future? (I don't know where the "other parts" start or how long in the future. Maybe beyond the termination shock and proved within a hundred years?)
Well humans can only observe a finite volume of the entire universe, so I don't know that cosmologists will ever be able to say that physics operates differently beyond that horizon. (But they might be able to infer some things based on gravity waves left over from the big bang, &c.) I think that observational checks for changes in the basic constants of physics have thus far failed show significant deviation at much earlier epochs of the visible universe, at least as far as I have read. That to me is mind blowing in itself, and lends significant weight to the concept of cosmic inflation.
Of course, answering this type of question is, itself, non-scientific. And probably, non-Wikipedian Original Research as well. :-)
Yes, anything that can not be tested or observed is probably best left for philosophy.
Thanks again for all your help. --RoyGoldsmith (talk) 05:40, 13 August 2009 (UTC)
You're welcome.—RJH (talk) 16:57, 13 August 2009 (UTC)
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