In this staff report, SDSTAFF Chronos gives (in my reading, anyway) the impression that our knowledge of the Milky Way’s structure is more vague than it really is. We have done better mapping than “there’s a bulge, and probably a bar, and…”
However, I agree that the “you are here” T-shirts are amazingly inaccurate; with the amount we know about our own galaxy, why are they using one that looks like Andromeda?
Mostly because the Milky Way probably looks a lot like Andromeda. And a majestic spiral looks better on a shirt than a fuzzy blobby thingy.
That said, please understand that even the central bar is not widly accepted as “fact”. There is strong evidence, but even its proponents wouldn’t call the issue settled. (If they were to, how could they get grants for more Hubble time?)
I betcha that if we could get way, way outside our galaxy and look back at it, it’d really look like a smiley face…
Given the fact that a feature as major as the bar wasn’t even discovered until a few years ago, I think that my vagueness was justified. There are more detailed measurements that can be made, but those are mostly in the “ongoing research” I mentioned. The page from the Electronic Sky is really not much more than an artist’s conception, itself: There’s a little more detail on the region close to us (which is, of course, the part we know best), but you’ll notice that the arms aren’t labelled on the other side.
And Dex, I agree. There’s probably some species out there whose face looks like a spiral when it’s happy 
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Chronos said:
Nametag said:
Chronos, I disagree. I think the reason the galaxy used on those “you are here” t-shirts look like Andromeda is because they probably use a picture of Andromeda. Why use an artist’s conception, when they can plug in a picture? As for why Andromeda, they’re a little easier to come by. 
And while I’m ranting, that website by Nametag said:
WTF?Why is “the Galaxy” not allowed to have a name? Our planet has a name: Earth. We don’t call it “the Planet” (capital “P”). Sure, the Solar System is the name of our “solar system”, but that’s because calling all star systems “solar systems” is coopting the proper noun. Sol is one of the names of our “sun” (The Sun), so calling our star system “the Solar System” is proper and referring to other stellar systems as “solar systems” is inappropriate.
But our galaxy is named “The Milky Way” because we discovered that the fuzzy band we call the Milky Way is our galaxy. So what if the only part we can make out is the fuzzy band, and that is how it got its name? The English language is full of bizarre, complicate, inexplicable methods for arriving at names for objects. In the grand scheme of things, this one seems downright logical.
And perhaps tangentially…
Let us also remember that it’s only “The Milky Way” to a certain segment of the Earth’s population. For example, some Native Americans referred to it as a “Path”.
http://www2.semo.edu/mast/edney.htm
http://www.gods-heros-myth.com/namerican/stars.html
Or cornmeal.
http://www.kstrom.net/isk/books/children/ch7.html
To the Mayas, it was a road.
http://www.windows.ucar.edu/tour/link=/mythology/Maya_Milkyway.html
In some Asian myths, it’s a river.
http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970511c.html
It’s only a “milky” way to a milk-drinking culture.
The Hindi term for it is the Great Sky River, which I think beats the pants off of ‘Milky Way,’ which sounds like it was coined by a four-year-old. It’s more poetic by a millionfold.
I do like the candy bar, but I read a few years ago that some people were referring to a nearby Galaxy as “Snickers.” That annoys me. I for one don’t enjoy lame product placement on Earth (i.e. corporate names on sports arenas), the last thing I need is for it to spread to the universe at large.
snicker
snicker
As far as Galaxy/Milky Way, another complication is that Galaxy means… You guessed it: Milky Way. Originally, we thought that the big clump of stars we lived in was the only thing of its type in the Universe, and because the most visible manifestation of it was the band of light in the night sky, it was named the Galaxy, proper noun. In the days of Hubble, though, it was realized that many of those hazy things we see in the sky (previously called nebulae) were, in fact, objects of a very similar sort. A general term is now needed for this class of objects, so they’re called galaxies, uncapitalized.
We humans–or at least we English-speaking humans–have kind of a bad track record in this regard. Historically, our particular planet has been called “the Earth” or even “the earth”; a simple “Earth” is relatively recent. (“Terra”, used in a lot of old science fiction, doesn’t seem to have caught on.) Similarly, our moon is “the” Moon (only science fiction fans ever call it “Luna”; even NASA calls it “the Moon”); our star is “the Sun”; so it’s perfectly in keeping with this conceited tradition to talk about “the Galaxy”.
And as already pointed out the proper name “Milky Way Galaxy”, if fully translated, would mean “Milky Way Milky Thing”.
I just realized that I didn’t address Irishman’s first point, about pictures of M31 being passed off as our own Galaxy. It’s true, many (though not all) pictures of a galaxy are of M31 (it’s an artist’s conception (or yet some other galaxy) if it’s shown face-on, rather than heavily inclined), but I couldn’t think of how to work that in without jumping ahead prematurely to the part about “looking at other spiral galaxies”.
While we’re on the topic of names, by the way, a pet nitpick: “Andromeda” is not the name of a galaxy, “The Andromeda Galaxy” is the name of a galaxy. “Andromeda” is the name of the constellation which just happens to be in that region of the sky, as seen from Terra (Ha! Young SF fans use it occasionally, too!). If “The Andromeda Galaxy” is too wordy for you, then you can just call it M31, a perfectly valid designation for it, being the thirty-first item on Messier’s list of Fuzzy Things in the Sky that Aren’t Comets.
Dear C.
I my self am a much more prisise but mild manner Freshman in highschool but my experience in star gazing has given me a thought. In finding the distance between two given points no matter it be two stars or two points on a plane using the given points p and y Y being our selves or our standpoint and another given point P it being a known position such as a moon or planet. and taking the relation between the two given points and the two unknow points then trangulating the distance based on c= p*cos(angle g(between p and y) (0 or 180 degrees) and dividing by r (radians per second)
I’m not quite sure what you’re getting at, there, Kame Kuroma. I presume you’re actually commenting on the earlier report on stellar distances? It sounds sort of like you’re describing the method of trignometric parallax, except that trignometric parallax doesn’t involve time. The only other possibility I can think of is that you’re referring to something moving across the sky at some known true speed, and measuring the apparent speed across the sky to determine distance. While this is a valid method for measuring distance, it’s of limited usefulness, since we very seldom know the true speed of an object in the sky. The only case I know of where it’s been used is Supernova 1987a: As the light from the supernova travels through the gas and dust cloud around the (former) star, it illuminates the cloud, and we can measure how the size of the illuminated portion is growing.
Have you seen the image at the bottom of this page?
I’ll note that we do indeed have a good idea of quite a bit of structure in the Milky Way. Radio mapping shows the arms fairly well, since it traces the dust clouds inside them. The bar in the center is a subtle feature, and difficult to see. I have not heard that the bar is in any real doubt, but I am not an expert in bar structures. I did write about spiral structure for astronomy.com, however.
We have also detected stars in the Mily Way’s halo, confirming the existance of it as well. I think that’s pretty cool.
Ken Croswell wrote a book called “The Alchemy of the Heavens”, about the structure of the Milky Way, which is pretty good. It has quite a bit about how the shape of the Galaxy has been determined.
Bad, how does one get distances from the radio measurements? Resolution isn’t nearly good enough for trignometric methods, and there aren’t many spectral features in the radio range to use.
As for halo stars, that’s actually not so impressive. Barnard’s Star, the next closest star after [symbol]a[/symbol] Cen, is (if I’m not mistaken) a halo star: The entire disk overlaps with the halo.
I don’t know if there are ways of directly measuring distances of radiosources, but one indirect technique would be to find stars that are probably assocated with the radiosource and use standard methods of distance measurement (cephids, supernovae, etc).
Measuring with string, just by stretching a string from here to the nearest star, is probably not often used, eh?
I remember doing this in grad school a long time ago. This site looks like it has a good description (it’s a PDF file). Try a web search on “Oort’s constants radio milky way”, which is how I found that site.
I dunno, it looks to me like that PDF is just assuming distances, to plug into the other equations. It’s a good description of how to measure the rotation, given the distances, but it doesn’t go into detail on how to get the distances in the first place.
sford, ordinarily one can measure the distance to radio sources using an optical counterpart, but the whole reason we’re using radio sources here in the first place is that the optical sources are obscured by the dust.