Talk:Milky Way/Archive 4

Archive 1

Archive 2

Archive 3

Archive 4

Archive 5

Archive 6

Off-topic text from another article

This is an off-topic section from galactic coordinate system. I am dropping it here for now. It's more or less redundant with a section in this article. Tfr000 (talk) 19:56, 23 July 2012 (UTC)

Galactic rotation

Galaxy rotation curve for the Milky Way. Vertical axis is speed of rotation about the galactic center. Horizontal axis is distance from the galactic center. The sun is marked with a yellow ball. The observed curve of speed of rotation is blue. The predicted curve based upon stellar mass and gas in the Milky Way is red. Scatter in observations roughly indicated by gray bars. The difference is due to dark matter or perhaps a modification of the law of gravity.

See also: Galactic rotation curve

The galactic coordinates approximate a coordinate system centered on the Sun. While its planets orbit counterclockwise, the Sun itself orbits the galactic center in a nearly circular path called the solar circle in a clockwise direction as viewed from the galactic north pole, at a distance of 8 kpc and a velocity of 220 km/s, which gives an approximate galactic rate of rotation (here at the location of our solar system) of 200 million years/cycle. At other locations the galaxy rotates at a different rate, depending primarily upon the distance from the galactic center. The predicted rate of rotation based upon known mass disagrees with the observed rate, as shown in the galaxy rotation curve and this difference is attributed to dark matter, although other explanations are continually sought, such as changes in the law of gravitation. The differing rates of rotation contribute to the proper motions of the stars.

Star chart w/ Milky Way

I went ahead and worked over File:MessierStarChart.svg - removed all of the M-objects and projected it onto the inside of a sphere. I will leave it up to the editors of this article what you want to do with it. Tfr000 (talk) 18:13, 26 July 2012 (UTC)

For it to be "large enough to reveal relevant details" (wp:image) it would have to be larger than a standard 220px thumb and go in "Appearance" section. So it would go where File:Milky Way Arch.jpg is now. I'm 50/50 on that leaning toward the map over Milky Way Arch.jpg. With an appropriate description it would put the point across more succinctly. Fountains of Bryn Mawr (talk) 20:17, 26 July 2012 (UTC)

Notes WEASEL/OR?

Per this edit (and this edit), "Some sources hold" is a WP:WEASEL beginning. The remainder looks like it combines a definite statement by Pasachoff with observation of use in the other sources leading to a WP:OR statement. If the other sources cover nomenclature please re-add them citing the exact nomenclature. Fountains of Bryn Mawr (talk) 18:04, 8 January 2013 (UTC)

The Milky Way is somewhat like another galaxy of its own108.212.253.7 (talk) 21:43, 25 February 2013 (UTC)

nomenclature

opening line: "The Milky Way is the galaxy that contains our Solar System" should be : "The Milky Way is the galaxy that contains THE Solar System" or: "The Milky Way is the galaxy that contains the stellar System that the planet earth is a member of" SentientSystem (talk) 03:18, 23 March 2013 (UTC)

There is large amounts of talk (and apparent consensus) on this topic above on this talk page. Fountains of Bryn Mawr (talk) 17:41, 23 March 2013 (UTC)

Thickness

I can't find any other sources that support this 1000 ly claim. The current source is from a question which was asked and answered in 1998. Th4n3r (talk) 00:55, 14 April 2013 (UTC)

The number hasn't changed appreciably since 1998 (or 1958, I think); it's in any textbook as well. Here's a recent review article which includes it, which I'll add to the article: arXiv:1301.3168. (Note that heights are most often quoted as a scale height, which is the height from the midplane to the point where the density is 1/e times that at the midplane; the thickness is twice the scale height. However, there enough different components of which you could measure the scale height that the uncertainty is about a factor of two. The most sensible thing to quote as one thickness is the thin stellar disk, which has a scale height of 100-350 pc.) —Alex (ASHill | talk | contribs) 01:18, 14 April 2013 (UTC)

Thank you. Th4n3r (talk) 07:03, 14 April 2013 (UTC)

Stars timelapse

Two users (or one user twice?) have added this movie: File:Stars Timelapse from Cape Town South Africa.webm. I'm not sure what it adds, and it doesn't play in my browser (Safari on a Mac or iPad), instead downloading as a file that opens (and plays) in Firefox. Does it really add anything to the article? I'm inclined to delete it, as it was once. —Alex (ASHill | talk | contribs) 00:17, 24 April 2013 (UTC)

It plays fine for me, (Chrome on Windows 8) but I have removed it as it appears to be nothing more than a pan across a starfield which I agree adds nothing to this article. Reatlas (talk) 05:12, 24 April 2013 (UTC)

Good article suggestion

I think that this should be identified as a good article. What do you think? Megahmad (talk) 16:09, 17 July 2013 (UTC)

It's not far from it, but there is one original research/citation needed tag and a handful of paragraphs with few or no references. —Alex (ASHill | talk | contribs) 23:18, 17 July 2013 (UTC)

OK thank you Alex. Yes I noticed that some sections or paragraphs lack citations or sources. I hope we see it as a "Good artice" in the near future. Megahmad (talk) 00:47, 18 July 2013 (UTC)

GA Review

This review is transcluded from Talk:Milky Way/GA2. The edit link for this section can be used to add comments to the review.

Reviewer: Jens Lallensack (talk · contribs) 18:53, 31 July 2013 (UTC)

I will review it. --Jens Lallensack (talk) 18:53, 31 July 2013 (UTC)

Thanks for your time and concern of reviewing it, as the GA nominator of it I actually I didn't contribute to the article but it's sad that for such an article that is well made and well written and lacks no sources or citations to not be a good article. So I thought it's about time to re-nominate it. Thank you again. Megahmad (talk) 22:13, 31 July 2013 (UTC)

Sorry that it took a few days, I'm not an expert on this topic and had to acquaint myself with it. The article is certainly comprehensive and accurate, but some sections may lack stringency. Here are my notes:

Section "Galactic center"

• That section is a bit confusing. It is not made explicit what the difference between the "bar" and the "bulge" is, but this may be essential for the understanding of this section.

Y OK – now there is a good hint in the introduction.

Section "spiral arms"

• Counts of stars in near infrared light indicate that two arms contain approximately 30 % more red giant stars than would be expected in the absence of a spiral arm, while two contain no more red giant stars than regions outside of arms.[66][67] – and further below – Two surveys of near-infrared light, which is sensitive primarily to red giant stars and not affected by dust extinction, detected the predicted overabundance in the Scutum–Centaurus arm but not in the Carina–Sagittarius arm.[66][67] -> Thats the same information, in two differend paragraphs. Should be merged. Perhaps simply remove the first sentence (that sentence seems a bit out of place, it does not explain what this observation means and may irritate the reader).

Y

• Paragraph: Another interesting aspect is the so-called "wind-up problem" of the spiral arms. … An inline citation for this paragraph would be nice. We may should remove the word "interesting" because its evaluative.

Y

Section "halo"

• Paragraph: The Chandra X-ray Observatory has provided evidence that the halo contains a large amount of hot gas. … It is not clear if the "halo" this paragraph is refering to is only the hot gas halo, or the halo as defined in the sections above. The section does not fit well into the rest of the article.

Y

• "While the disk contains gas and dust which obscure the view in some wavelengths, the halo component does not." – The halo component contains no gas: This is inconsistent to other statements in the article, e.g. "the halo contains a large amount of hot gas". The whole paragraph may is better merged with the first and introduction paragraph of the "halo" section, because it does not recite certain recent studies but is more general.

Y

Sections "Sun's location and neighborhood" and "age"

• There still is a paragraph labeled with "citation needed" and "original research?" in the "Sun's location and neighborhood" section, and there is an "not in citation given" label in the "age" section; this should be resolved.

Y

Section "Environment"

• The section Environment is not well equiped with inline citations. Especially, an inline citation for this statement would be great: "The stream is thought to have been dragged from the Magellanic Clouds in tidal interactions with the Milky Way."

Y

• "In January 2006, researchers reported that the heretofore unexplained warp" … this paragraph, reciting a single study, seems a bit to detailed in comparison with the rest of the article; it could be much shorter.

Y

Section "Etymology and mythology"

• The section seems a bit unbalanced. There is a whole paragraph about the sanscrit, but no mention of other cultures as described in Milky Way (mythology). Perhaps we should simply merge the sanscrit section with the latter article. --Jens Lallensack (talk) 10:40, 4 August 2013 (UTC)

Thanks for your points, actually you're right and most of what you've said is right and needs corrections in the article, you look at things different than I do, maybe I was fast to nominate it and I should've checked it better before nominating it, anyway, it's good to point these things out so other people beside me and you can work them out and make a better article, we can work to improve it and I am sure it will be a GA in no time. Is there anyway that more people can see your notes (above) on this matter so they can improve the article? Thanks for your effort and it's really appreciated. Megahmad (talk) 21:58, 4 August 2013 (UTC)

I've addressed several of the points. Particularly, I think I've addressed the spiral arms, halo, location and neighborhood, age, and environment comments. The list of satellite galaxies in environment isn't explicitly cited, but I think that's OK as there's nothing likely to be challenged in there. —Alex (ASHill | talk | contribs) 22:30, 6 August 2013 (UTC)

Thanks for your time ASHill, these are really good improvements to the article, and thanks for Jens Lallensack for the throughout review of the article, I'm sorry if I may not be able to contribute to the article even though I am the one who nominated it as GA, and that's because I am still learning about the topic and I found out that the article was good enough for me before nominating it. Anyway, it's nice to see that the article is being improved even if it doesn't end up being a GA. Megahmad (talk) 00:00, 7 August 2013 (UTC)

I don't interpret the review as a fail; just some comments needed to reach GA status. The normal procedure is to give editors a week or so to address issues before a final failure is assessed. (Obviously, it's Jens Lallensack's call, not mine.) An outright fail wouldn't normally have a relatively short list of points to address like this. I'll try to address the remaining points, though the etymology stuff is way outside my area -- would be great if someone else helped! —Alex (ASHill | talk | contribs) 01:57, 7 August 2013 (UTC)

Yep, my point was that Jens Lallensack's revealed issues are good for the article so people can help to remove them like you did with some of them. And the article is not at all far from being a GA. It just needs some little work. Megahmad (talk) 02:52, 7 August 2013 (UTC)

I'm glad that you find my comments helpful. Of corse its not a fail, nor was the nomination prematuraly, its absolutely normal for an article this magnitude that issues will pop up during review. Now there are only two issues left. I'm will think about what to make with the Etymology and mythology section. --Jens Lallensack (talk) 08:06, 8 August 2013 (UTC)

The paragraph or section that contains: illustrating the fact that most stars are less bright than absolute magnitude 8.5. and it has "Citation Needed" and "Original research?" tags at the end, can we add this source for it and remove the tags: the pdf file at www.astronomie.cz/data/2009/04/00-atlas-85.pdf It's talking about the whole magnitude and distances about the stars. Megahmad (talk) 20:30, 8 August 2013 (UTC)

I added a different source (which is used on star), tweaked the text, and removed the or tag. —Alex (ASHill | talk | contribs) 12:43, 9 August 2013 (UTC)

OK Thanks! Megahmad (talk) 13:23, 9 August 2013 (UTC)

I still have no ideas how to improve the Etymology and mythology section, but this issue may is compatible with GA criteria. I will pass the article now. Thank you, everybody, for your great work on this very important article! --Jens Lallensack (talk) 19:13, 9 August 2013 (UTC)

Thanks for your hard work Jens and to everyone who contributed to improve this article especially Alex. Well done guys. Megahmad (talk) 19:44, 9 August 2013 (UTC)

Indeed; thanks, Jens, for the helpful review and Megahmad for the nomination which prompted us to clean up several things. —Alex (ASHill | talk | contribs) 22:47, 9 August 2013 (UTC)

Minimum age

The lead section says: "The oldest known star in the Galaxy is at least 13.6 billion years old, about as old as the Universe". Should be rephrased to "...close to current estimates of the age of the Universe itself". Of course neither the beginning of the Milky way, nor its earliest stars, could be close to touching the time of the big bang - that's plain to people who have read astronomy a bit but not as obvious to all ordinary readers. The way it's phrased now it suggests that the oldest stars in the Milky Way formed just, well, a couple thousand years after BB.Strausszek (talk) 20:15, 6 August 2013 (UTC)

I cleaned it up. (That sentence was added just hours before your comment by another editor.) —Alex (ASHill | talk | contribs) 22:44, 6 August 2013 (UTC)

Vandalism

I've seen a bit of vandalism invading this page, some are Good-faith and some are not. However, can we semi-protect it from editing especially after it has become a GA? Thank you. Megahmad (talk) 19:52, 9 August 2013 (UTC)

I don't think the level of vandalism merits semi-protection; it's not enough that it's hard to deal with. It's good faith edits by a few registered users that sometimes do as much harm as good that are harder to deal with, since some of the edits are improvements so simply undoing the edits is unfair. —Alex (ASHill | talk | contribs) 22:26, 9 August 2013 (UTC)

Ashill's revision

Ashill undid my post on the derivation of the Milky Way, and the name galaxy from the Greek myth of Hercules, as unimportant and repetitive. It is true that it is covered right at the end of the article, but so is much other information covered in the introduction and enlarged upon later. The association of galaxies and milk is important and should be briefly covered in the introduction. For this reason I have reversed the deletion. John D. Croft (talk) 04:20, 26 August 2013 (UTC)

The association of galaxies and milk is already covered in the previous sentence in the introduction: "Its name "milky" is derived from..." It is also covered in the parenthetical immediately before this new addition ("milky circle"). Also, the Greek creation myth is not the only one to include milk. In addition, this article is not about mythology; we have a separate article that is (Milky Way (mythology)). Thus, I think mentioning Heracles in the intro is overkill, but I'll wait for comment before reverting. Note that if we do include the myth, we should use the same name for Heracles in the body and intro. —Alex (ASHill | talk | contribs) 21:46, 26 August 2013 (UTC)

The way I see it, the Hercules / Hera myth is only pertinent in the lead if it explains the name derivation in English (this being the English Wikipedia). The article states (if its referenced correctly) that our English name comes from the Latin "via lactea", milky road or way, not the Greek. There is more than one Greek myth and many other cultural myths, so best left in their own section. Fountains of Bryn Mawr (talk) 01:40, 27 August 2013 (UTC)

I don't think it should be mentioned in the intro section especially that it's a myth, it's better stay in the mythology section. So my vote is to delete this paragraph and it's really not important to be mentioned (at least not in the intro section). --Megahmad (talk) 15:10, 28 August 2013 (UTC)

Agreed, not notable enough for lead. — Reatlas (talk) 13:11, 30 August 2013 (UTC)

Astronomical Terms

So, if I get this straight, if the Milky Way Galaxy was compared to...say, the USA, would our Solar System (and Earth for that matter) be considered part of the "redneck, hillbilly" region, and the galactic arms closer to the center of the galaxy be the "hip, coastal areas", with Saggitarius a* obviously being Washington, DC? I just want to get things in perspective. 50.36.81.177 (talk) 04:26, 15 October 2013 (UTC)

Vandalism again and lots of it...

Last time when I suggested to make this article semi-protected someone told me that there isn't enough vandalism to semi-protect it and mostly it was good faith edits and I think they were right about that, but now I see a lot of vandalism conquering this article in the last few months (as seen on its edit history) and most of them are not good-faith ones. So I again nominate to semi-protect this GA. What do you think? Megahmad (talk) 20:15, 24 November 2013 (UTC)

Unclear sentence

I'm unclear what this sentence is trying to say:

The central bar, delineated by red clump stars, shows that x-ray emissions show elongation in alignment with surrounding massive stars.

Please could somebody clarify it and fix the repeat use of 'show'? Praemonitus (talk) 15:57, 27 December 2013 (UTC)

Agreed that that sentence was a mess. I clarified, I think going to what the sentence was supposed to mean. —Alex (ASHill | talk | contribs) 21:06, 28 December 2013 (UTC)

Thank you. Praemonitus (talk) 06:00, 30 December 2013 (UTC)

Context

The following paragraph appears almost out of context, as though it had been copied from a more general discussion regarding spiral galaxies:

Another aspect is the so-called "wind-up problem" of the spiral arms. If the inner parts of the arms rotate faster than the outer part, then the galaxy will wind up so much that the spiral structure will be thinned out. But this is not what is observed in spiral galaxies; instead, astronomers propose that the spiral pattern is a density wave emanating from the Galactic Center.[90] This can be likened to a moving traffic jam on a highway—the cars are all moving, but there is always a region of slow-moving cars. This model also agrees with enhanced star formation in or near spiral arms; the compressional waves increase the density of molecular hydrogen and protostars form as a result.

Please could the specific relevance to the Milky Way be clarified? Otherwise I think it should be removed. Praemonitus (talk) 16:08, 27 December 2013 (UTC)

There were no objections so I removed it. Praemonitus (talk) 23:01, 11 January 2014 (UTC)

Floating in space

I have a question. If I was floating in neighboring space, so that I had a complete spherical view (no earth to block half the view), would the Milky Way take up 180 degrees of my view, or circle all around me, or what? Comments? Pb8bije6a7b6a3w (talk) 00:37, 25 May 2014 (UTC)

Spiral pattern rotation period confusion?

The value for spiral pattern rotation period (50 Myr) implies that the corotation radius is much less the orbital radius of the Sun. The reference for this value uses the following notation for the spiral pattern rotation speed: Ωsp ≈ 20 Gyr^−1, and it also states that for this rotation speed the corotation radius is beyond the orbit of the Sun. May be this value means not "rotation cycles per billion years", but "radians per billion of years" (in physics, angular velocity usually uses angular units), and the value of the rotation period needs to be multiplied by 2*pi, i.e., should be 314 Myr? — Preceding unsigned comment added by 91.187.17.89 (talk) 19:03, 13 June 2014 (UTC)

What part of the Milky Way is studied?

Two apparently simple questions, related to each other, to which I cannot find a quick answer anywhere:

1. In which part of the Milky Way galaxy have we already studied the stars, contained in it? so that we know for sure its three-dimensional stellar structure. Or, in other words, in which part of the Milky Way stars are observable with current scientific instruments?

2. How many stars from all the stars contained in the Milky Way galaxy are catalogued and studied? -- 178.19.251.112 (talk) 10:26, 16 September 2013 (UTC)

good questions, with no simple answer: (1) it depends on the instrument you are using to make the study, and the type of star being studied. within the limits of the question, the "full 3D sample of stars" in the Galaxy, very faint type M stars and brown dwarfs are exhaustively mapped only out to a few dozen parsecs ("volume limited" or exhaustive stellar samples end at around 25 parsecs); most main sequence stars are mapped in 3D out to a few hundred parsecs; giant stars even farther, but hit or miss depending on their location. satellites have extended the horizon so far to about 1000 parsecs for parallax and basic spectroscopic typing, and in the near future will extend it to several thousand parsecs, but again the brightness of the stars, and the presence of obscuring gas and dust, mean the sample is not exhaustive and the farthest of those will be viewed above or below the galactic disk. (2) it depends on which catalog you mean: the yale bright star catalog has about 9,000 stars, the tycho catalog has about 1 million, and the Gaia catalog when completed will have about 1 billion. the total number of stars in the Galaxy is estimated to be perhaps 120 billion or more. Macevoy (talk) 22:23, 5 July 2014 (UTC)

Disc thickness - not 1000 light years

Could people please read sources of this page correctly as in one of them the writer actually mocks wikipedia for using his page as a source and getting it completely wrong.

Link to article: http://scienceblogs.com/startswithabang/2012/05/31/how-big-is-our-galaxy/

Quote:"If you ask wikipedia, they’ll send you here, which as of today — I’m sorry to say — gets it wrong by quite a bit. Our galaxy is much thicker than the 1,000 light years figure they quote. But how much thicker? Even among scientists today, that’s up for debate."

I just thought I would bring this to your attention as there may be many more serious mistakes like this one.

Kind Regards Joe — Preceding unsigned comment added by 130.209.157.26 (talk) 15:22, 21 January 2014 (UTC)

It depends what you count. The 1000 ly figure is about right (and properly cited) for the thin stellar disk, which is the bulk of the stars in the Galaxy, if you count the thickness as twice the exponential scale height (but 33% of the stars are more than one scale height from the plane, by definition of scale height). As someone who makes his living studying the gas that link talks about, I wouldn't argue that it really represents the "true" thickness of the Galaxy. The text of the article makes this distinction, but the infobox doesn't. —Alex (ASHill | talk | contribs) 22:20, 21 January 2014 (UTC)

"On average" is hardly a distinction, unless I have missed something in which I apologise, however the main issue I was trying to get across is that an article should not cite sources which completely contradict and ridicule the original statement. Also as an astrophysics student I know that within the sun's distance from the centre of the galaxy the disc thickness is 1kpc, should this data not also be included in the infobox (e.g ≈ 0.3kpc - 1kpc). As even though most of the stars (95%) lie in a thin disk, with a vertical scale height ≈ 300 pc, the rest of the stars (including our sun) form a thick disk with a vertical scale height ≈ 1 kpc.

Kind Regards

Joe

I don't actually see a reference to the scienceblogs.com blog post you mention, despite its claim that the Wikipedia article cites it. Instead, I see a citation to NASA's Ask an Astrophysicist, which directly supports the 1000 ly statement, and to an Annual Reviews of Astronomy & Astrophysics, which also supports the claim. (The peer-reviewed journal article is obviously a stronger source, but they agree.) Which source in the article conradicts the statement made? If you point me to it, I'm happy to fix it, but I can't find the problem. And my textbooks all refer to the Sun as a thin disk star. —Alex (ASHill | talk | contribs) 09:23, 22 January 2014 (UTC)

By the way, you don't need to register or "become a member" to edit the article; you're welcome to edit it yourself to fix the issue. (This is much easier than talking about it in the abstract.) Because this article has been subject to vandalism in the past, it is "protected" so your edits will have to be approved by an established user, but that will happen quickly. —Alex (ASHill | talk | contribs) 10:13, 22 January 2014 (UTC)

I apologise as I too am unable to find the source for this article, even though I am positive this is where I found it. Anyway thank-you for your time and fixing this article, however I am still not sure why my online lecture notes state 'disc thickness: 1kpc (at sun's distance from centre of galaxy)' perhaps a typo :).

Kind Regards

Joe

The point of the dimensional measurements is relative: the thin disk *of stars* is about 300 parsecs thick, measured as a scale height or a vertical span bracketing a minimum density of stars. but the density is fundamentally variable. the jibe about "that's a matter of debate" is specious, since any argument is a matter of semantics, not substance. the disk of the Galaxy thins in height gradually out to a thickness of about 1000 to 2000 parsecs, and from there thins out even further into a halo of stars that forms a flattened sphere. The disk of interstellar gas is confined to a scale height of about 50 parsecs. The stellar central bulge is perhaps 10 times thicker than the stellar disk, and the disk thins out from the center to the edge. we are talking about an enormous swirling mass of billions of stars with very near a fluid independence of motion, not a compact disk or radial tire, so dimensions have to be handled as approximations -- not as uncertainties. Macevoy (talk) 22:24, 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)

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)

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)

Pictures Missing

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)

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)