Talk:Milky Way

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The pictures on this page are not working and clicking the link to the pictures results in a 'you must be logged in to edit this page' notice. I'm not sure why that is, I've never seen anything like it. — Preceding unsigned comment added by 75.71.82.192 (talk) 22:57, 3 September 2014 (UTC)

The first sentence of the article—again. This is the Solar system, not the Earth!

Hi everyone!

Surfing Wikipedia during my ordinary day I just came across this article, and the starting sentence (which is considered to be the most important one) hasn't left me comfortable with it. The Milky Way is the galaxy that contains the Earth. Eh, what? My immediate thought was "of course it would be better to say Solar System instead of Earth", so I did this edit.

To much of my surprise, when I came back several days after, I found my humble edit reverted with a comment: "Unfortunately on Wikipedia you have to "show your work" ;). This is covered on the talk page". And again my first thought was, "what?! I've been reading and editing Wikipedia for years (mostly Russian edition though), never heard of a need to describe a one phrase edit on a talk page!".

But when I drifted here I was surprised even more. I found here a whole section long discussion about why we should't use the Solar System in the first sentence. Oh come on guys, this is ridiculous! First of all: does anyone seriously think that the Solar System can be interpreted in any other way than our one? Has anyone even read scientific (and popular) papers, all of which of course refer to it exactly as the Solar System? Has anyone seen than even the ref from the first sentence uses "the Solar System" everywhere across definitions, not "the Earth"?

Milky Way does not "contain the Earth" in the usual meaning of this. This sentence is simply misleading and erroneous, it directly implies that the Earth is a rogue planet with no parent star, orbiting directly in the gravitational field of the galaxy. So the right and nice introduction to this article, in my very very strong opinion, is: The Milky Way is the galaxy that contains the Solar System.

Please let's sort this question out and continue make Wikipedia even better. Sorry for this pretty long post, I was really surprised and shocked (and I still am) :-)

Kirill Tsukanov (talk) 21:18, 30 October 2012 (UTC)

The question may be asked "why limit to "Solar System"? Why not "... that contains a local group of stars that include the Sun" or "... that contains many solar systems including our own". "Earth" is the minimal unit. Also Wikipedia is an encyclopedia of common language and the trackers of common language point the same question that shows up on this talk page "the Solar System? ... which solar system?"[1]. We could always change it to "...contains our Solar System".... but that brings up the question why is a "solar system" a limiting unit? Milky Way does not "contain the just the Solar System". Fountains of Bryn Mawr (talk) 03:16, 31 October 2012 (UTC)

Kirill is absolutely correct. We limit it to our Sun's solar system, not to a planet within that system. When this article was a Good Article, we said it was the "home of the Solar System". When we are talking about the scale of galaxies, we are not speaking in terms of planets, but in terms of stars. Viriditas (talk) 05:58, 31 October 2012 (UTC)

The scale between a planet and a solar system compared to the scale of a galaxy is so small it makes no difference. So there would have to be some other reason to limit to "solar system". Fountains of Bryn Mawr (talk) 21:14, 31 October 2012 (UTC)

A galaxy is a group of stars, so referring to our solar system and not our planet is appropriate to scale. We don't say the Milky Way contains the planet! We say the Milky Way contains our solar system. When we talk about the Milky Way, our reference point is our Sun, not our planet. Our Sun is one of billions of stars in the Milky Way. We don't say our planet is one of billions in the galaxy in the first sentence because galaxies are classified as groups of stars, not planets. Viriditas (talk) 21:48, 31 October 2012 (UTC)

I'll repeat what I said last time this came up. A galaxy is a collection of many things: stars, planets, interstellar gas and dust, dark matter, gravitational potential. The reason the Milky Way is particularly interesting is because we live in it; the point of mentioning the Earth or the Solar System in the first sentence is to convey that as concisely and clearly as possible. More detail in the first sentence is unhelpful because most (but not all, I suspect) readers know it anyway. I think "Earth" does that better than "Solar System"; I think "the Sun" would also be better than "the Solar System", though I prefer Earth. What this article said when it was a good article is not terribly relevant; it's not like this one word is the difference between good article and not. What I feel most strongly about is that we should continue to have exactly one term (any of these three are OK), not a list. —Alex (ASHill | talk | contribs) 21:56, 31 October 2012 (UTC)

I strongly disagree. What the article said when it was a GA is incredibly relevant because it demonstrates stability over a period of years, a stability based on solid sourcing and wide agreement across many different editors. Our best sources on the subject discuss the galaxy in terms of stars and solar systems. We talk about our place in the galaxy on that scale, not on the scale of planetary systems. The planet Earth should not be in the lead. Viriditas (talk) 22:11, 31 October 2012 (UTC)

Yes, and that's exactly what the second paragraph of the lede does (quite well, in my opinion). Again, it's the fact that we on Earth are inside the Milky Way that makes it fundamentally more important to us than any other galaxy; we're not mentioning the Earth or the Solar System because of its importance to the Galaxy. The literature discusses galaxies primarily in terms of gravity, dark matter, gas, star formation, star clusters, spiral arms and structure, stars and stellar (not planetary) systems; planetary systems aren't dynamically important to galaxies and can only be seen very locally. On a galactic scale, no individual star or stellar system is important; by that logic, we shouldn't mention the Solar System at all and should lead with a description of the dynamical properties of the Milky Way, like "The Milky Way is a star-forming galaxy, one of two large spiral galaxies which dominate the Local Group". —Alex (ASHill | talk | contribs) 22:37, 31 October 2012 (UTC)

See the previous stable lead linked in the article history header. The Solar System is mentioned in the second paragraph. There's a lot of things that are more important to us because we are on Earth, but we should remain neutral in our approach. The reason we favor mentioning the Solar System as our point of reference rather than the Earth is because that's the point we use to measure our place in the galaxy in comparison to other stars that compose the galaxy. The Earth is not a unit of comparison on that scale. We are not the center of the Solar System, nor are we the center of the galaxy. The current wording implies an importance and placement that does not exist. Viriditas (talk) 23:02, 31 October 2012 (UTC)

Wikipedia has processes for discussions like these, that's why they require refs, the references that was used had it listed as 'our solar system', and not the 'Earth', but that was to a Elementary school dictionary. I found some better refs for it as our 'Solar system' Oxford dictionary, Webster's and Britannica, and it shouldn't be changed unless better references are found. (Floppydog66 (talk) 23:35, 31 October 2012 (UTC))

Think we should remove the refs to Oxford dictionary, Webster's and Britannica - lets get some real books on the matter if refs are needed.Moxy (talk) 23:41, 31 October 2012 (UTC)

IMO both viewpoints ("earth" and "solar system") are academically ok - and "weigh" pretty much the same in my mind at the moment - but since only one view can prevail I would choose the "earth" view for Wikipedia - after all - the "earth" view will likely be more easily understood by more people likely to be reading Wikipedia - a phrase like "solar system" otoh, although also academically ok of course, will not be as easily understood by as many readers I would think - in any case - Enjoy! :) Drbogdan (talk) 00:07, 1 November 2012 (UTC)

Academically, the Earth is not a reference point for positioning ourselves in the Milky Way, the Sun is. Our place of reference is in the Solar System, which is part of the Local Interstellar Cloud, within the Local Bubble, on the inside edge of the Orion–Cygnus Arm, located within the Milky Way. Viriditas (talk) 04:13, 1 November 2012 (UTC)

Those aren't just books they are organizations, that define English versions of words, and their usage. Using things like Carl Sagan, or scholastic books would only be regional at best, while those sources cover all of English speaking countries, and can be found in China and other countries where the English meaning was being looked up. The closest thing to an international description would be more like the International Astronomical Union. (Floppydog66 (talk) 01:27, 1 November 2012 (UTC))

FWIW - Definition of "Milky Way" by the NASA Space Telescope Science Institute (related to the Hubble Space Telescope and James Webb Space Telescope) is as follows => "The Milky Way, a spiral galaxy, is the home of Earth." - hope this helps in some way - Enjoy! :) Drbogdan (talk) 02:45, 1 November 2012 (UTC)

Drbogdan, the link you cite was written for children in eighth grade, between the ages of 13-14.[2] Do you really think that is an appropriate reference for our task at hand? I don't. Viriditas (talk) 04:08, 1 November 2012 (UTC)

@Viriditas - Thank you for your comments - I entirely agree with you - I'm flexible on the issue - after all, all views so far presented (ie, the "Milky Way" includes "earth", "sun" and "our solar system") are factually accurate - and any of the views, at any age I would think, entirely appropriate - seems the average age of Wikipedia readers is 36 years old but at what average educational-level? - I would think it less than professional-level or college-level but really don't know at the moment - at what educational-level should Wikipedia articles be presented? - perhaps this is somewhat relevant to the present discussion? - in any regards - Thanks again - and - Enjoy! :) Drbogdan (talk) 15:06, 1 November 2012 (UTC)

Brief followup (and if interested) - seems Wikipedia articles are written "too sophisticated for its audience" according to a relatively recent essay => < ref name="KA-20120924">Anderson, Kent (September 24, 2012). "Wikipedia's Writing — Tests Show It's Too Sophisticated for Its Audience". Scholarly Kitchen. Retrieved December 7, 2012.</ref> - The "Readability/Flesch Score" for the Milky Way article is 50 (60 or lower may be too difficult for most Wikipedia readers?) (Score of 60/"6th grade/11yo" level best for Wikipedia readers?) - in any case - Enjoy! :) Drbogdan (talk) 21:16, 7 December 2012 (UTC)

Except, that has nothing to do with the current discussion. Viriditas (talk) 23:40, 7 December 2012 (UTC)

I *entirely* agree with the results of the current discussion - my comments refer to the issue raised in this discussion (which I appreciate) re reading level of the article - and thought it thereby relevant to the present discussion - in any case - enjoy! :) Drbogdan (talk) 00:27, 8 December 2012 (UTC)

Though sources are certainly useful to see how others describe the Milky Way, there's no dispute on the facts here, and all the facts are properly cited. It's entirely an editorial choice, which (to my understanding of policy) isn't bound by references. —Alex (ASHill | talk | contribs) 03:04, 1 November 2012 (UTC)

So far the only two sources for the use of "the galaxy that contains Earth" have been both for children, with talking down to the reader. This is why actual refs don't word it this way. Consensus is reached by providing facts and not feelings and likes or dislikes. The first sentence was being discussed when it was changed from 'the solar system' to Earth as well and one reference given which didn't mention Earth at all. If the wording is contested, then references to other reliable sources will need to be given, so far their have only been two given, both of which have been contested by me and Viriditas. (Floppydog66 (talk) 07:43, 1 November 2012 (UTC))

Okay, I think what we have now is just great: "our Solar System" is even better than "the Solar System". The new refs are very good and settle the debate, thank you, Floppydog66. Kirill Tsukanov (talk) 11:53, 1 November 2012 (UTC)

"our Solar System" looks familiar and seems to be the lest linguistically tortured of the bunch, so looks good to me. Fountains of Bryn Mawr (talk) 13:34, 1 November 2012 (UTC)

Hi guys, just popping in here. I never bothered to participate in this debate because it seemed far too trivial for me, but I hope we have finally reached a resolution and that no changes to the lead definition and debates will happen again in the future. "Our Solar System" sounds perfect, and I never did like the use of Earth in the definition instead. Cadiomals (talk) 22:39, 14 January 2013 (UTC)

Um, should it not be "the Solar System" instead, to align it with Earth and Human?

As far as the general reader is concerned (the targeted audience of Wikipedia) there is more than one "Solar system"[3]. Fountains of Bryn Mawr (talk) 14:33, 18 February 2013 (UTC)

No there isn't, we call everything else Planetary systems and Star systems. Ours is the most relevant and the one we call the Solar System, no need for "our". And you're not supposed to use "our" in anything. Look at the Human article, it's written from a alien perspective, but limited to our knowledge. So you can say humans are important, just not say "we" are important. --occono (talk) 16:19, 18 February 2013 (UTC)

Well thanks for the personal opinion on what we should call things but there are sources that are generally considered more authoritative than personal opinion. As for "our", its only a restriction for a point of view inconsistent with WP:NPOV. Everyone reading Wikipedia is in this solar system, so "our" is everyone's point of view. Fountains of Bryn Mawr (talk) 19:28, 18 February 2013 (UTC)

Okay, no need to be snarky. Just confused about the distinction because everyone reading the Human page is a Human but it's still written to be from a external perspective rather then everyone's point of view. :/ --occono (talk) 20:39, 18 February 2013 (UTC)

The problem with using only 'Solar System' is that the only source that calls other systems 'Planetary systems' is the "The Universal Book of Astronomy" written by one guy, and not an institution. There are no other general purpose books that use this. Oxford, Webster and most general definition books use 'Solar System' still to describe other systems. Even though 'Sol' of Solar system means 'our' star. But for now the word Solar System has more then one meaning, and needs to be defined at the beginning of the article. If you can find more sources that use 'Planetary systems' it would help, but until the general usage is Planetary systems', for Extra-Solar Systems, the 'our' clarifier should stay. So far there has been only one other clarifier suggested to replace it, but it didn't keep the scale representations. Just like 'The Milky Way contains the USA' wouldn't work. (Floppydog66 (talk) 00:53, 19 February 2013 (UTC))

Sounds like you should change the Solar System, Star system and Planetary system articles then. They give the impression that only our planetary system is called a "Solar System".--occono (talk) 01:03, 19 February 2013 (UTC)

Yes that's the problem, all three of those articles titles are based on one source, that isn't backed up by other general use sources. (Floppydog66 (talk) 02:48, 20 February 2013 (UTC))

There is only one Solar System, i.e. the system of the Sun. Other systems are planetary systems. Saying "our Solar System" is just a tautology. Similarly, there is only one Sun, i.e. the star around which Earth orbits. The other hot hydrogen-fusing balls of gas are stars, not suns. --JorisvS (talk) 19:17, 11 December 2013 (UTC)

Not to reopen something that seems settled but here is the reasoning.

• "There is only "one" Solar System, i.e. the system of the Sun. Other systems are planetary systems" - do you have a reliable source for that?
• "There is only one Solar System" - Merriam-Webster says no. The reader thinks (or knows) there is more than one, so we should say which one we mean.

Fountains of Bryn Mawr (talk) 20:20, 11 December 2013 (UTC)

Why not say "the Sun" or "Earth" in place of "the Solar System" or "our Solar System"? There is no ambiguity about either one of these (perhaps very slightly less ambiguity about "the Sun"). Given the disagreements amongst editors, it seems certain to me that there must be some lack of clarity for readers with either variant of "Solar System". —Alex (ASHill | talk | contribs) 21:49, 11 December 2013 (UTC)

Well, I'm not denying that other planetary systems are often imprecisely referred to as "solar systems", though never as "the Solar System". If people have a moment of confusion, the Solar System article and the link at the top of it should make the distinction clear to those, and actually inform them about it. --JorisvS (talk) 13:39, 12 December 2013 (UTC)

per WP:NOTTEXTBOOK articles should have obvious meaning in the text. We should not force the reader to follow a link to gain the meaning from it. Again, is there a source that says it is imprecise to refer to other planetary systems as "solar systems"? Fountains of Bryn Mawr (talk) 21:08, 12 December 2013 (UTC)

How does that apply? It is not "textbook style" (i.e. teaching style) to be precise, consistent in wording, and not use tautological words. In fact, that is professionally encyclopedic. --JorisvS (talk) 21:17, 12 December 2013 (UTC)

You cannot assume the reader understands the precision (as they may in a text book). The reader should be able to infer the meaning from the text, not follow a link to get the meaning. Fountains of Bryn Mawr (talk) 21:38, 12 December 2013 (UTC)

Actually, because textbooks are for teaching the subject matter, they should not assume that the reader understands the precision. An encyclopedia can assume this, as long as readers who do not understand it are not left stranded in the dark (which they quickly aren't if they follow the link). --JorisvS (talk) 09:06, 13 December 2013

For a general article topic, current consensus on Wikipedia is not to assume the reader understands the precision, or anything about the topic (WP:AUDIENCE). Fountains of Bryn Mawr (talk) 15:58, 13 December 2013 (UTC)

Well then, what about "the Solar System (i.e. Earth's planetary system)", that would really be helpful to the lay reader. --JorisvS (talk) 16:23, 13 December 2013 (UTC)

Not sure how that would be helpful since the reader will say "which solar system? If you mean capital "Solar System" = us?.... that's a Wikipedia construct, no reader is expected to know that. Fountains of Bryn Mawr (talk) 15:33, 14 December 2013 (UTC)

I don't understand what you mean by that response. "Earth's planetary system" is completely unambiguous and is used to clarify "the Solar System" for those who would ask that question. --JorisvS (talk) 12:25, 15 December 2013 (UTC)

hmm... misunderstood when you said what about "the Solar System", that seemed pretty clear. "Earth's planetary system" would be a little more wrong because Earth does not have a planetary system, the Sun does. Fountains of Bryn Mawr (talk) 19:36, 15 December 2013 (UTC)

"i.e. the Sun's planetary system" is also fine by me. The Solar System is Earth's planetary system in that Earth is part of it, although it is not defined by it. --JorisvS (talk) 21:20, 15 December 2013 (UTC)

Here's a fresh perspective for you: as of now the wording reads "our solar system" which is clear, direct, and inclusive, and I strongly suggest we keep it the way it is. Jusdafax 09:29, 13 December 2013 (UTC)

How's that a fresh perspective? --JorisvS (talk) 09:33, 13 December 2013 (UTC)

I have never commented here previously and come to the article with fresh eyes. And this article is much to my liking. In my view it is worthy of a push to FA. Jusdafax 09:55, 13 December 2013 (UTC)

Okay. Could you also elaborate how you think it is "direct" and "inclusive"? --JorisvS (talk) 10:01, 13 December 2013 (UTC)

Viriditas and others above make an excellent case for "solar system" over "Earth" - in my thinking this is an obvious choice. But I see you have just been reverted over the "our" part, which I actually did not know until just now. My words "direct" and "inclusive" are in reference to both the intellectual and emotional reaction I get in locating where I am in the cosmos from reading the lead sentence. I find the use of "our" reader-friendly yet encyclopedic. Further, as a very amateur astronomer who never ceases to be amazed when gazing at the pinpoint moons of Jupiter, or the rings of Saturn, much less the distinct patch of fuzzy light that marks the Andromeda Galaxy, I think the use of "our" is marvelous, a kind of "you are here" marker that makes me think of Carl Sagan. I see you object in your edit summary that the term is a tautology, which I assume you mean as "self-reinforcing." I appreciate your concerns but think that in this case, in an article called "Milky Way," that Fountains of Bryn Mawr is in the right of it. However, I salute your passion, and admire that you care enough to make the effort to edit here, but must agree with Fountains that consensus was established on this issue well before I arrived. Happy sky-watching to you and all! Jusdafax 10:47, 13 December 2013 (UTC)

Somewhere earlier in this long discussion of principles, semantics and policy it might have been useful to ask, what is the point of reference for professional astronomers? For example, if astronomers publish a diagram of the Galaxy (its correct name, by the way: "Milky Way" is the name for the appearance of the Galaxy in the sky) how do they indicate the location of the observer? It's unambiguous: they mark the location of THE SUN. Macevoy (talk) 22:27, 5 July 2014 (UTC)

Number of stars doesn't match the sources

The page lists the number of stars in the Milky Way as "400 billion (4×10^11 ±2×10^11)". The first source it cites, http://web.archive.org/web/20090412172631/http://mynasa.nasa.gov/worldbook/galaxy_worldbook.html, says the number is 100 billion (10^11). The second source, http://www.universetoday.com/102630/how-many-stars-are-there-in-the-universe/, says UP TO 400 billion (4x10^11). I'm not sure how those numbers became "(4×10^11 ±2×10^11)" — Preceding unsigned comment added by 140.211.14.191 (talk) 20:19, 15 May 2014 (UTC)

Agreed, The article even contradicts itself, stating "up to 400 billion" here. And in the same sentence, this citation states "our galaxy contains a minimum of one planet for every star on average", implying there are 100 billion stars. In addition, http://www.nature.com/scitable/blog/brain-metrics/are_there_really_as_many cites one of the same sources, but uses the phrase "somewhere between 200 and 400 billion".

I think the Number of stars section in the Infobox should be changed to read "200-400 billion", and subsequently (3×10^11 ±1×10^11). Greggydude (talk) 08:34, 9 June 2014 (UTC)

These estimates need to be put in context to make sense to the average reader. the high estimates include white dwarfs and brown dwarfs down to limit of the largest gas giant planets, neither of which are "stars" in the sense of bodies emitting light generated from nuclear fusion, and many of which emit almost no light at all; the counts are also highly conjectural. if stars means "those bright things you see in the night sky" then the consensus estimate is probably closer to 120-150 billion (it has increased over time). Macevoy (talk) 22:25, 5 July 2014 (UTC)

Thickness vs width ratio

This statement is not intuitive to me; can someone either correct (if it's a mistake) or add an explanation why two different ratios appear: "The stellar disk of the Milky Way Galaxy is approximately 100,000 ly (30 kpc) in diameter, and is, on average, about 1,000 ly (0.3 kpc) thick.[2][3] As a guide to the relative physical scale of the Milky Way, if it were reduced to 100 m (110 yd) in diameter, the Solar System, including the hypothesized Oort cloud, would be no more than 1 mm" ie is it 100,000 : 1000 (1%) or is it 100,000mm : 1mm (0.001%) — Preceding unsigned comment added by 81.108.105.120 (talk) 13:07, 18 June 2014 (UTC)

Radius of galactic stellar disk = ~19,000 parsecs. radius of the solar system, including oort cloud = ~0.3 parsec. 0.3/19000 = ~0.000016. 100m x 0.000016 = 0.0016m = 1.6mm. Macevoy (talk) 22:25, 5 July 2014 (UTC)

Higher order news

Astronomy now floods us with high-order new information about the World of the Solar System and related concepts. To be sure, it is welcome after thousands of years of ignorance. Young people are sometimes left hoping for seasoned, expert answers. No such luck. That new knowledge will surprise life on Earth for millennia. It would be good for expert teachers to introduce the idea that modern techniques presents an unprecedented flood of high order information, likely to keep Earth in uproar for centuries. Just think of Saturn's big hexane molecule, if that's what it is, and the geysers on Titan. Planets share much with the very origins of life. A new order of understanding will be expected to scale all that and more. It is a rich world for new teachers. SyntheticET (talk) 02:37, 30 July 2014 (UTC)

New lower mass for the Milky Way

Diaz et al. (2014) recently published a new estimate for the mass for the Milky Way of 0.8 ± 0.5 x 10¹² M☉, it is same within error of earlier estimates.

Diaz, J.D., Koposov, S.E., Irwin, M., Belokurov, V. & Evans, W. 2014. Balancing mass and momentum in the Local Group. arXiv preprint arXiv:1405.3662. http://arxiv.org/pdf/1405.3662v2.pdf

--Diamonddavej (talk) 02:51, 31 July 2014 (UTC)

Relative size visualization is incorrect

This statement in the Size and mass section has two problems:

Alternatively visualized, if the Solar System out to Pluto were the size of a US quarter (25 mm in diameter), the Milky Way would have a diameter of 2,000 kilometers, an area approximately one third the size of the United States.

First of all, a diameter (one dimension) cannot be compared with an area (two dimensions). This could be fixed by changing area to length (or just dropping it entirely) and size to breadth or similar.

Secondly, it would still be wrong after such a change. That would make the breadth of the U.S. 6000 km, whereas 4300 km or so is closer to the mark, depending on where you measure it.

How about this (ignoring the planetary status of Pluto for now, and making it a little less U.S.-centric):

Alternatively visualized, if the Solar System out to Pluto were the size of a US quarter or 1-Euro coin (25mm, 23mm respectively), the Milky Way would have a diameter of 2,000 kilometers, or approximately half the breadth of the United States or Europe.

Mathglot (talk) 21:15, 9 September 2014 (UTC)

Had another look at this to check the math and it turns out that the original value of 2,000 km is correct, it's only the comparison to the U.S. that was wrong.

Based on an assumption of 11.8 billion km (11.8 * 10**9 km) for the average diameter (twice the radius) of Pluto's (highly elliptical) orbit, reducing that to 25mm is a reduction factor of 472 trillion. Reducing the Milky Way (diameter 9.46 * 10**17 km) by an equivalent amount yields a diameter of 2,004 km. So that value looks okay.

Mathglot (talk) 23:10, 9 September 2014 (UTC)

Yet another problem: it appears that the WP editor who added the section on the size analogy and added a reference for it misinterpreted what was meant by "the Solar System" and mistakenly added the words "out to Pluto" in an apparent attempt to clarify this point. Unfortunately, he got it wrong as the Solar System is measured to Neptune's orbit now and although the reference does not make this clear, the math does.

Further, the incorrect "one third" U.S. size claim in the WP article is not supported by the reference. In fact, the reference says:

"Imagine that our entire Solar System were the size of a quarter. ... On this scale, the diameter of our Milky Way galaxy will be about the size of the United States!"

This is, in fact, accurate using the recently adopted notion of the Solar System, i.e., out to the orbit of Neptune. Whoever added the words 'out to Pluto' in the WP article did not get them from the reference. Would've been nice if the Smithsonian article had been more explicit about this, but given that the math for "about the size of the United States" requires a Solar System diameter of approximately Neptune's orbit, I'm changing the article to read thus:

Alternatively visualized, if the Solar System out to Neptune were the size of a US quarter (25mm), the Milky Way would have a diameter of 4,000 kilometers, or approximately the breadth of the United States.

This hews more closely to the reference, and is accurate.

Mathglot (talk) 19:48, 19 September 2014 (UTC)

I'm not aware of any source that states the Solar System only extends to the orbit of Neptune, which would be a diameter of ~60 AU. The Solar System is the Sun along with everything orbiting the Sun. The Oort cloud orbits the Sun, and if you counted it the diameter would be more like 100,000 AU. Primium mobile (talk) 14:43, 9 October 2014 (UTC)

You're quite correct about that as one definition of the solar system, but that doesn't affect the discussion above a jot, as we're talking about calculations based on what the sources say. Please reread it. Mathglot (talk) 09:56, 19 October 2014 (UTC)

I don't need to reread it. You're nitpicking the "out to Pluto" reference when it doesn't make any difference. The ratio of solar system diameter to Milky Way diameter, with the level of accuracy that is being used, is not going to change the result. We don't even know the exact diameter of the Milky Way. We have a 20,000 LY difference between the high and low estimates of the diameter. No one is even sure how to define the "edge" of the Milky Way. So, my point is that the rewording shouldn't say "out to Neptune" at all. It should just say "solar system" just like the original source states. When dealing with such large margins of error, just saying "solar system" instead of "solar system out to Neptune" is more than sufficient. Primium mobile (talk) 14:19, 22 October 2014 (UTC)

I really, really doubt that anyone other than experts can "visualize" the Solar System; the scale of distances is beyond normal human experience. Hence, any comparison of the "size" of the Solar System to that of the galaxy is going to be abstract. There is, imho, WAY TOO MUCH emphasis and 'ink' being used. You have, it seems to me, three reasonable measures of physical volume of the Solar System: to the heliopause, to the 'edge' of the Oort Cloud, or to Neptune's apogee. I suggest that rather than using a multitude of similar comparisons, you agree to choose ONE that is most understandable to the widest audience.216.96.76.190 (talk) 04:38, 11 December 2014 (UTC)

No, you also aren't getting what I am saying. We do not know how large the Milky Way is. We could be off by as many as 20,000 LY. The diameter Neptune's orbit is at right around .0013 LY. That is .0000065% of the margin of error on the diameter of the Milky Way. The Heliopause is right around .0032 LY in diameter. That is .000016% of the margin of error on the diameter of the Milky Way. Finally, the Oort Cloud is thought to start at about .8 LY. Even that is only .004% of the margin of error on the diameter of the Milky Way.

The point is that, no matter what measurement you use for the size of the Solar System, the differences are only a tiny fraction of the uncertainty in the size of the Milky Way. So we shouldn't be specific on what is meant by "Solar System" because that gives an answer with greater precision than the numbers you started with. Primium mobile (talk) 17:42, 16 December 2014 (UTC)

Granting everything you said about precision, margin of error and the illy-defined or uncertain boundaries of the solar system and the Milky Way, you still miss the point I'm afraid. If you reread the source (which I'm aware you already said you don't need to, nevertheless you do need to if you are to get the point) you would find a size analogy whose math is correct only for a solar system whose size equates to the diameter of the orbit of Neptune. Regardless whether you're more correct about the Solar System being defined out to the Oort cloud or the heliopause or any other limit of your choosing, the math in the reference would be orders of magnitude off with the current analogy, given your definition. It's clear that what they meant was the man-in-the-street version of the Solar System (and whether you choose Neptune or Pluto hardly matters much, as they intersect). If you want to insist that the Solar System is 100,000 AU, fine, I have no problem with that, but then you'll need a new analogy and a new source containing it to back it up, as the current analogy cannot hold up with a 100,000 AU Solar System, as the math is way off. Now you see the point?

Mathglot (talk) 01:19, 31 January 2015 (UTC)

I see the point, and I don't need to reread the reference because that's not what I am talking about. I know what it says. What I am saying is that you can not get an answer with a greater order of precision than what you start with. It's not mathematically sound. Usually, if you divide two by three, you can assume that what you are doing is dividing 2.000000000000000... by 3.0000000000000... In this case, it's more like 2.0000000000001 divided by 3.00000000000089, and you arriving at .666... That's not the way math works. You are applying too great of a precision to the outcome when we don't know the input to any degree of precision at all. That's why I think this size reference should either be left intentionally vague or it should be removed from the article. You don't have to agree with that, and I'm not going to make any edits to contradict yours. I'm just telling you why I think you are wrong. Primium mobile (talk) 17:08, 27 February 2015 (UTC)

Problem with the Milky Way's description and size.

This article is tragically unclear about its subject. For instance, is the Milky Way the stellar (visible) disc or is it the gravitationally bound objects which include (as a minor part) its stars? In fact; its both, and more. Some use the term to refer to the disc, some to its visible star (systems), some include the (hydrogen) gas and dust, and some include the dark matter, while others include dwarf galaxies (& clusters) in our galactic neighborhood. If I was writing it, I'd start with the earliest understanding (band of light) move on more recent ones (the whole Universe) and then to the understanding that our galaxy is one of many, finally ending up with the idea that the Milky Way is a spherical cloud of dark matter which contains a disc of (orbiting) visible stars as well as smaller (dwarf) galaxies orbiting/attracted to it. I'd include estimates of its mass (total, stars (and planets), gas and dust, and dark matter, and black holes) and the fraction of those components NOT in the galactic disc. The various estimates of number of stars, length and thickness of the disc, and overall diameter could usefully be compiled in a table, I'd guess. I'd probably also include some discussion of the estimated number of various classes of stars (perhaps in another table) as well as the age distribution. Recent work (2014) estimates that up to half of the normal matter of the Milky Way is outside of the disc. I don't know if this work is widely accepted by the experts, buts its been peer reviewed/published (perhaps Science, IDK, but thats where I read about it). So, we believe the Milky Way first started 'forming' shortly after the Big Bang (first 10 million years). Last I heard, we're not sure which came first, population III stars (the first stars) or the Milky Way. We're also not sure when Sag A* got its start - was it a cause of the galaxy formation or a result? Its an active area of research/modeling. Then the most active star formation period, about 4 billion years ago and now we are in a large galaxy in its middle age, where most of the stars it will ever form, are already formed. We believe that in roughly 4 billion years we will collide with Andromeda. While that collision may change the orbits of most of the stars in both, it is likely that the two galaxies will generally 'pass through' each other with relatively few physical collisions between stars. As stars use up their fuel, the appearance of the Milky Way will change. Few stars will be created 10 billion years from now. I'd also mention that the majority of the Milky Way is NOT visible, rather it is obscured by its many dust clouds. IMHO, the fact that the spiral arms don't describe stable structures (long term persistence) as the individual stars orbit is also given short shrift here. I'd also mention that we have recently identified one star which possibly originated in the same cluster as the Sun. Since we expect we had hundreds of sibling stars, this discovery marks a exciting epoch in understanding how the Milky Way evolved over time.216.96.76.190 (talk) 05:18, 11 December 2014 (UTC)

So do that. No one is stopping you. Primium mobile (talk) 17:44, 16 December 2014 (UTC)

Lede contains a citation that is wrong.

I was motivated to look up and read the paper cited (as of Jan 11, 2015) as [22], by Sandage. There is NO mention in that paper that "billions of galaxies" exist. While there is mention in the paper of Hubble's galaxy counting work, no numerical values are provided, hence the citation is simply wrong. My motivation was my curiosity about whether in the decade between 1925 and 1935 the experts had reached a consensus on the number of galaxies. (We still don't know how large our Universe is. We should only discuss the Observable Universe, but its likely that the 'whole' universe is infinite.) I was under the impression that millions rather than billions were also considered by some as the actual number, back then. So I am challenging the assertion that Hubble "showed that the Milky Way is just one of many billions of galaxies." (Last sentence first paragraph of lede). Either provide a valid citation for this, or just say "many galaxies". Good estimates of the number would come later, imho.Abitslow (talk) 23:44, 11 January 2015 (UTC)

I disagree with this a bit. Hubble was able to observe a fairly uniform distribution of galaxies in the universe, as well as observe enough galaxies with differing amounts of red shift to formulate Hubble's Constant, which can tell us how far away a galaxy is. If you know the distribution and you know the volume you can get a rough estimate for the number of galaxies. So while Hubble himself may not (I don't know if he did or not) have arrived at a number in the billions for a galaxy count, it was his work that allowed others to do so. Primium mobile (talk) 17:15, 13 January 2015 (UTC)

A probably more correct thing to say is that "Hubble showed that the Milky Way is just one of many—now known to be billions—of galaxies." —Alex (ASHill | talk | contribs) 19:21, 13 January 2015 (UTC)

Yeah, I could go with that. Primium mobile (talk) 20:10, 13 January 2015 (UTC)

Astronomical history

The estimation for the number of stars in milky way has seen a dramatic increase even in last 30 years. Therefore, astronomical history section of the article should contain past estimations, such as the ones mentioned here. Logos (talk) 19:11, 26 January 2015 (UTC)

Oldest known star

Something I'm working on tracking down: the article's treatment of the "oldest known star" is a bit of a mess. The infobox has one, the lede a second, the text a third, all of which are inconsistent and give no synthesized picture. (I'm sure this has arisen because each time there's a new study or press release that claims to have found the latest oldest known star, someone adds it in one place but not the others.) A review article or the introduction of a paper with some sort of summary would be best; I'll try to track one down. —Alex (Ashill | talk | contribs) 17:50, 16 March 2015 (UTC)

Old Disk Population

Various articles on Wikipedia use the term "old-disk star", but they don't explain it. Could that term—and/or old disk population—be covered somewhere in this article?[4] It seems appropriate. Praemonitus (talk) 21:26, 20 March 2015 (UTC)

Sifting through the center of milky way galaxy

By observing and sifting through the center of milky way galaxy scientists have understood the importance of dust in formation of stars and planets. Continue reading here:

http://phys.org/news/2015-03-milky-center-unveils-supernova-factory.html?utm_source=nwletter&utm_medium=email&utm_content=splt-item&utm_campaign=daily-nwletter

MansourJE (talk) 13:23, 24 March 2015 (UTC)

Units for angular momentum

Very simple: I want to look up the angular momentum of the Milky Way, and I find it listed with the units J s/rad. This may be the way some cognoscenti describe angular momentum, but I just want standard units, like J s. I don't want to have to read up on why it is divided by radians. — Preceding unsigned comment added by Ripetti (talk • contribs) 03:17, 2015 April 15 (UTC)

Hi, I urge you to take this question to reference desk. On talk pages we only discuss about how we can improve an article. Thank you! --Chamith (talk) 03:36, 15 April 2015 (UTC)

Actually, because it is not the normal unit in which angular momentum is expressed, this is appropriate to mention here. We should convert that unit to typically understood units, maybe alongside the value in its current unit. --JorisvS (talk) 07:53, 15 April 2015 (UTC)

When the unit is expressed as J s, it is implicitly J s/rad, since radians are dimensionless. Astronomers (and thus astronomy articles) often like to be explicit that the radian is hidden in there (and because astronomers will sometimes express angles with degrees, arcminutes, or arcseconds, depending on context). But 1 J s = 1 J s/rad. —Alex (Ashill | talk | contribs) 13:41, 15 April 2015 (UTC)

I know the rad is dimensionless, but it is still a meaningful unit, which can be seen from the conversion of rad/s to Hz. The formula for angular momentum is L=Iω, with I=[kg m²] and ω=[rad/s], so L=[kg m² rad/s], which gives [J s rad], not [J s/rad]. Something isn't adding up. --JorisvS (talk) 14:19, 15 April 2015 (UTC)

(ec) I see that the cited source doesn't actually include the "/rad", so I removed it. (As noted, it doesn't change the number.) However, specifying one angular momentum for the Milky Way is a questionable exercise, as it depends entirely on the radius you choose. The cited source just uses it as a unit, not really in the context of the Milky Way, and I can't find any other source that gives a number. The closest I can find is Figure 7 of this paper, which plots angular momentum as a function of radius. But I can't find any other source that quotes the total angular momentum of the Milky Way. Given that the source we have is somewhat questionable, I'm not sure the angular momentum should be in the article at all. —Alex (Ashill | talk | contribs) 14:25, 15 April 2015 (UTC)

150-180 kly

The Milky Way is now know to be 150-180 kly, not 120kly. Please do not make ANY reversions to this without proper research AND discussing here. Do NOT vandalize the article by changing it back simply because you don't like change. It MUST be discussed. 66.190.94.33 (talk) 20:43, 1 June 2015 (UTC)

This is discussed in the lede of the article. You're changing the number in the infobox. The larger diameter is from one recent study (and accompanying press release and media coverage). It's better to be conservative until this is more widely confirmed when just reporting one number, with more detail and the latest result in the text. I did change the infobox to say "at least 100–120 kly". —Alex (Ashill | talk | contribs) 20:48, 1 June 2015 (UTC)

Fine with going this direction, but changed ambiguous "at least" 100ly to 100-180ly. Journal article has not yet been refuted, and this is actually follow-up research of research done many years ago. Large range is acceptable. 66.190.94.33 (talk) 21:05, 1 June 2015 (UTC)