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What Exactly Is a Galaxy?

Soulskill posted more than 3 years ago | from the will-smith-will-figure-it-out dept.

Space 225

sciencehabit writes "Surprising as it may sound, astronomers don't have an answer to this basic question. There's no agreement on when a collection of stars stops being a cluster and starts being something more. Now, in an echo of the recent wrangling over Pluto's status as a planet, a pair of astrophysicists from Australia and Germany want to start a debate on the issue — and they have even set up a Web site for people to cast their votes." While we're on the subject of galaxies, reader mvar pointed out that astronomers using data from Hubble have spotted what could be a new record holder for the most distant known galaxy, located roughly 13.2 billion light years from Earth.

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Samsung (2, Funny)

Anonymous Coward | more than 3 years ago | (#35036312)

It's a phone right? Most likely to be running Android

Re:Samsung (1)

fridaynightsmoke (1589903) | more than 3 years ago | (#35036406)

C'mon, every fool knows that a Galaxy is a chocolate bar made of the same chocolate that Snickers/Mars are coated with...

Either that or a Ford MPV

Re:Samsung (0)

Anonymous Coward | more than 3 years ago | (#35036522)

No. It's a cellphone.

You both win! (2)

A nonymous Coward (7548) | more than 3 years ago | (#35037034)

Is it a flip- or slide-open cell phone? No? Then it must be a candy bar cell phone.

Re:Samsung (0)

Anonymous Coward | more than 3 years ago | (#35036808)

Snickers and Mars don't have the same chocolate. Mars's is darker.

Re:Samsung (1)

mangu (126918) | more than 3 years ago | (#35036764)

no, it's a whole bunch of stuff [wikipedia.org] .

Re:Samsung (0)

Anonymous Coward | more than 3 years ago | (#35036842)

No, it's anything bigger than your mom.

Re:Samsung (0)

Anonymous Coward | more than 3 years ago | (#35037418)

No, it's anything bigger than your mom.

That rules out everything except for your mom, though!

Galaxies are social constructs. (0)

Anonymous Coward | more than 3 years ago | (#35036324)

Galaxies are social constructs.

Stop that! (1)

Suki I (1546431) | more than 3 years ago | (#35036508)

Galaxies are social constructs.

That is how I lost my beloved Pluto! Now you people want to take away my pretty, swirly Galaxies! Wait, this one could go my way if I get a consensus on "swirly." I can concede pretty, but I am standing firm on swirly.

Voting? (5, Insightful)

SilverHatHacker (1381259) | more than 3 years ago | (#35036330)

It doesn't seem like the definition of a scientific term is something that should be left to a democratic vote. Public opinion with regards to science is never a good thing to rely on (creation vs evolution, naturalistic healing, etc).

Re:Voting? (2)

Takichi (1053302) | more than 3 years ago | (#35036408)

Maybe so, but it's a pretty good way to get people to read your paper. First question from the survey:

1. Have you read the paper by Forbes and Kroupa accepted for publication in Publications of the Astronomical Society of Australia entitled "What is a galaxy? Cast your vote here..." (its available at http://arxiv.org/abs/1101.3309 [arxiv.org] )

Re:Voting? (4, Funny)

pushing-robot (1037830) | more than 3 years ago | (#35036426)

A galaxy is a massive, gravitationally bound system consisting of at least one Stephen Colbert.

Re:Voting? (1)

Gaygirlie (1657131) | more than 3 years ago | (#35036540)

A galaxy is a massive, gravitationally bound system

Hey! Leavy my mom out of this!

Re:Voting? (0)

Anonymous Coward | more than 3 years ago | (#35036660)

Hey! Leavy my mom out of this!

I tried, but she is pretty much everywhere.

Re:Voting? (0)

Anonymous Coward | more than 3 years ago | (#35036820)

While I try to leave this (*points to his crotch*) out of your mom.
Sorry, you gave me the perfect setup

Re:Voting? (4, Insightful)

Daniel_Staal (609844) | more than 3 years ago | (#35036478)

Creation vs evolution is a discussion of theories and facts, and facts aren't really subject to public opinion.

However, this is just definitions. All we really need is some coherent way to draw the line between the two, and it doesn't really matter what the line is. The comparison to Pluto is apt: it didn't really matter whether Pluto was a planet or not, except that science works best with consistent definitions, and either we could use a definition that included Pluto and a couple dozen (at least) other objects in our solar system, or we could use the definition that excluded all of them, including Pluto. Basically the decision was that there would be less public outcry this way, and it made more 'sense'.

But it'd have been better to have the discussion earlier, which is what these people are trying to do: Hold the discussion early enough that the results will get used before the public at large get emotionally attached to the one or two border cases.

Re:Voting? (4, Insightful)

Fat Cow (13247) | more than 3 years ago | (#35036558)

It doesn't seem like the definition of a scientific term is something that should be left to a democratic vote. Public opinion with regards to science is never a good thing to rely on (creation vs evolution, naturalistic healing, etc).

It's not really a scientific term. No theories depend on the definition of a galaxy.

Re:Voting? (0)

Anonymous Coward | more than 3 years ago | (#35036644)

How about the theory that the Milky Way is a galaxy?

Re:Voting? (-1)

Anonymous Coward | more than 3 years ago | (#35036760)

Or my theory that you're the dumbest person in the galaxy?

Re:Voting? (0)

Anonymous Coward | more than 3 years ago | (#35036704)

Since when does a scientific term require a dependent theory? That's the second most ridiculous thing I've heard today.

Re:Voting? (2)

jd (1658) | more than 3 years ago | (#35037128)

No, but I would consider a scientific definition to require some very specific collection of theories and to not require non-theorized constructs of any kind. (Thus, requiring a planet to be a specific size or in a specific location is NOT a scientific definition; requiring it to have certain properties that a well-defined group of planetary-like objects will all share and all definitely non-planetary-objects will not possess is a scientific definition.)

It's the same way we define fundamental properties like distance in terms of fundamental constants. Distance is defined relative to the speed of light, for example.

Re:Voting? (4, Interesting)

icebike (68054) | more than 3 years ago | (#35036732)

It doesn't seem like the definition of a scientific term is something that should be left to a democratic vote. Public opinion with regards to science is never a good thing to rely on (creation vs evolution, naturalistic healing, etc).

But you miss the central point of the story.

There is no formal definition, scientific or otherwise. Its just a term in common usage with no universally agreed upon definition.

As such voting is as good a method of arriving at a definition as any other, and certainly a better method than was originally used (namely no method at all).

Re:Voting? (0)

Anonymous Coward | more than 3 years ago | (#35036830)

But in this case, it makes sense. "What exactly is a galaxy" doesn't matter to cosmology or astrophysics; it's just a definition, or a convention to call something as "galaxy". What should be defined as "galaxy" doesn't matter, except for consistency reasons; and that is why a vote, or an attempt to reach consensus, is the best way to reach a good definition.

Re:Voting? (0)

Anonymous Coward | more than 3 years ago | (#35036866)

If we are going to have a vote, let's be properly democratic and keep tally on a host running the Linux operating system.

err.... Linux is an operating system, right?

Re:Voting? (1)

jasnw (1913892) | more than 3 years ago | (#35036924)

First, I suspect that any response which does not indicate that the paper was read will be rejected out of hand. Second, I also suspect that they were not planning that this survey would be found by the Great Unwashed Masses. However, that said, I think it will be hard to get much useful out of this sort of polling once the voting moves outside the community that both cares about the answer and knows enough to vote intelligently (you know, like voters in the USofA). If this were just being answered by astronomers and researchers in related fields, the results could be a useful measure of what those who have a clue think about this. Otherwise, it's just wasted time and effort on everyone's part.

Re:Voting? (1)

Belial6 (794905) | more than 3 years ago | (#35037002)

You are misunderstanding the issue. When defining a scientific term like galaxy, vote is perfectly reasonable, as long as the definition is consistent. That is how naming things work. By definition, names are the sounds that people agree apply to specific things. Thus if the population decides that the sounds that make up sky mean the area in the air above us, then that is what it is. Creation vs. Evolutions, are not things that change by what we believe. We are either correct or incorrect. naturalistic healing either works or doesn't work. Voting does not change the laws of physics, but it certainly can change the rules of language.

Re:Voting? (1)

chichilalescu (1647065) | more than 3 years ago | (#35037226)

actually, I think voting for the definition of a term is just fine. the science resides in the accepted relationships between different terms, and that's not up for debate.

for an analogy, think of colors: suppose for some reason I want to call "green" what everyone else calls "red". I write a book where I say that the wavelenth of the color "green" is around 400 nm, and that's fine. It would be a problem if I also said that most plants have the color "green" as well --- that would be false (for earth, at least).

I assume you meant to say that the term "galaxy" should be applied to a reasonably complex system that has a few clear properties. However, I think the idea of voting on the term is just the idea of voting on which properties should be considered; the science doesn't change in any way.

Re:Voting? (3, Funny)

56ker (566853) | more than 3 years ago | (#35037470)

And there was me thinking it was a chocolate bar. :P ;)

Community standards (3, Funny)

paiute (550198) | more than 3 years ago | (#35036344)

I know a galaxy when I see one.

Can Pluto be a galaxy? (2)

ewg (158266) | more than 3 years ago | (#35036364)

Pluto's not a planet, maybe it's a galaxy!

Re:Can Pluto be a galaxy? (1)

Suki I (1546431) | more than 3 years ago | (#35036542)

Pluto's not a planet, maybe it's a galaxy!

Not swirly enough, but I like your thought :)

Better Be Careful... (2, Funny)

sottitron (923868) | more than 3 years ago | (#35036376)

...or we might wind up living in the Milky Way Cluster

Re:Better Be Careful... (2)

jason.sweet (1272826) | more than 3 years ago | (#35036878)

Wish I knew what you were looking for.
Might have known what you would find.

Standard for astronomy. (5, Interesting)

Anonymous Freak (16973) | more than 3 years ago | (#35036384)

Lots of astronomical terms are very vague in their definition. Heck, "planet" was only officially defined a couple years ago.

There is no "official" difference between "ocean" and "sea", either.

Re:Standard for astronomy. (1)

Shadow Wrought (586631) | more than 3 years ago | (#35036574)

Lots of astronomical terms are very vague in their definition.

True. Does the difference between a Cluster and Galaxy really amount to that much anyway? Pluto at least we were familiar with as a planet and a couple generations of kids, at least, were taught it was a planet. So chaning it actually did have some affect. If Cluster HG42 gets reclassified as Galaxy HG42, does that really change much?

Re:Standard for astronomy. (4, Interesting)

bunratty (545641) | more than 3 years ago | (#35036628)

It's the same for other subjects. In biology, there's no clear definition of the term species. You can define a species as a group of animals that can reproduce sexually with one another, but as far as I know there's no good definition of species for organisms that reproduce in other ways. Sometimes definitions are completely arbitrary, such as the difference between a tropical storm or a hurricane.

Re:Standard for astronomy. (0)

Anonymous Coward | more than 3 years ago | (#35036994)

Hurricanes goes whirl whirl whirl.

Tropical storm goes WHOOSH!

Re:Standard for astronomy. (1)

theBuddman (1905202) | more than 3 years ago | (#35037248)

I thought the difference between a tropical stom and a hurricane was that if it hits somewhere else, it's a tropical storm, but if lands where you live, it's a hurricane...

Re:Standard for astronomy. (0)

Luthwyhn (527835) | more than 3 years ago | (#35037516)

Wow, actually... no. I suppose the difference between tropical storm and hurricane is arbitrary, but it is in no way vague. The definition is based upon the maximum sustained windspeeds. If the windspeeds are at or above 74MPH, it's a hurricane. That's pretty straightforward.

Floridian in the hoooouse!~

Re:Standard for astronomy. (0)

Grishnakh (216268) | more than 3 years ago | (#35037546)

Nope, there's a clear definition of the terms "tropical storm" and "hurricane", and it depends on sustained wind speeds.

http://en.wikipedia.org/wiki/Tropical_cyclone [wikipedia.org]

This article explains the naming system, and how it differs in different places (e.g. they're only called "hurricanes" in the NE Pacific and north Atlantic, elsewhere they're called "typhoons", "cyclones", and "cyclonic storms", and the wind speed limits are all different).

Re:Standard for astronomy. (1)

iammani (1392285) | more than 3 years ago | (#35036882)

There is no "official" difference between "ocean" and "sea", either.

Is there a difference (even unofficially)?

Re:Standard for astronomy. (2)

Anonymous Freak (16973) | more than 3 years ago | (#35036930)

The best one I've heard of is that it's an ocean if it has ocean in its name. That's it.

Re:Standard for astronomy. (1)

Belial6 (794905) | more than 3 years ago | (#35037116)

Well, I have heard of inland seas, but never an inland ocean, so someone seems to have a line between ocean and sea. Not sure what it is, but it seems to be out there.

Re:Standard for astronomy. (1)

nschubach (922175) | more than 3 years ago | (#35037350)

So what about lakes and ponds?

I think people are too quick to rush to naming and categorizing stuff (in Astronomy and in life)... can't all bodies floating in space be called something like Satellites? Bound and unbound, just like landlocked and non-locked bodies of water. Earth would be a Bound Satellite where "Bound" was a term used for something with a regular orbit.

Re:Standard for astronomy. (1)

ILMTitan (1345975) | more than 3 years ago | (#35037290)

Oceans are bigger. So big, that there are only 3-5 of them: Arctic?, Atlantic, Indian, Pacific, Southern?? The smallest (the Arctic) is neary 5 times the size of the largest sea, which is similar in size to other large seas.

Re:Standard for astronomy. (0)

Anonymous Coward | more than 3 years ago | (#35037498)

If the body of water in question is a member of the seven seas then it is an ocean. Otherwise it's ... wait what?

mathematical formula ? (1)

KernelMuncher (989766) | more than 3 years ago | (#35036396)

I didn't RTFA but it seems like there should be a mathematical formula for mass & distance which could define a galaxy easily. There are obviously many well known cases which could be used as examples for the model.

Re:mathematical formula ? (1)

bunratty (545641) | more than 3 years ago | (#35036648)

Sure, but exactly where do you draw the line between a galaxy and a cluster? Is there a clear dividing line? If not, the division is arbitrary.

Re:mathematical formula ? (0)

KernelMuncher (989766) | more than 3 years ago | (#35036774)

I'm not an astronomer but don't galaxies generally spin while clusters just sit there and hang out.

Re:mathematical formula ? (1)

Elder Entropist (788485) | more than 3 years ago | (#35037036)

No. Clusters spin. Gravitationally bound, they would have to to maintain form and not all just collapse into a black hole.

Re:mathematical formula ? (1)

nedlohs (1335013) | more than 3 years ago | (#35037124)

Everything that is gravitationally either spins or collapses. "sit there and hang out" isn't an option.

Re:mathematical formula ? (1)

mrsquid0 (1335303) | more than 3 years ago | (#35037238)

Globular clusters and elliptical galaxies neither spin nor collapse. They are supported by the velocities of their stars.

Re:mathematical formula ? (1)

Belial6 (794905) | more than 3 years ago | (#35037136)

The next question would be, how much do they need to spin before it counts. If it is determined that the out edges of a cluster move 3 feet ever million years, does that count as spinning?

Distant Galaxy Now even Further (1, Informative)

spiedrazer (555388) | more than 3 years ago | (#35036464)

The interesteing thing not mentioned about the Distant Galaxy in the article. eventhough it's position 13.2 billion years ago was that far away from our current position, it is currently probably more like 45 billion light years away!

Re:Distant Galaxy Now even Further (1)

bunratty (545641) | more than 3 years ago | (#35036710)

Doesn't it depend on your frame of reference? In our frame of reference, it really currently is 13.2 billion light years away, isn't it? It's funny how many comments that involve relativity seem to implicitly assume there is one preferred frame of reference. Talk about not getting the point!

Re:Distant Galaxy Now even Further (2)

michaelwv (1371157) | more than 3 years ago | (#35037044)

It's not really about preferred frame of reference, it's the different meanings of distance that arise in general relativity. In this case there are two meanings being discussed:
1) How long has that photon been traveling to get to Earth ("light travel time")? 13.2 billion years
2) How far away is that galaxy right now ("proper distance"). I.e., if each galaxy had a clock that counted seconds since the Big Bang and could instantaneously extend a long ruler to the other galaxy and the ruler was sent and received at the same time has measured by those clocks, how long would that ruler be? 32 billion light years

There are other definitions, and you can make this arbitrarily more complicated by considering moving reference frames.

Re:Distant Galaxy Now even Further (1)

kenj0418 (230916) | more than 3 years ago | (#35037202)

2) How far away is that galaxy right now ("proper distance"). I.e., if each galaxy had a clock that counted seconds since the Big Bang and could instantaneously extend a long ruler to the other galaxy and the ruler was sent and received at the same time has measured by those clocks, how long would that ruler be? 32 billion light years

So, if there was no such thing as Relativity then. Didn't you just prove his point?

Re:Distant Galaxy Now even Further (2)

cforciea (1926392) | more than 3 years ago | (#35037280)

Methinks you do not grasp what general relativity has to say on the concept of simultaneity. You have to pick a frame of reference to talk about something happening "at the same time" because observing the same events at a different speed will cause them to occur at different times. To quote GP:

It's funny how many comments that involve relativity seem to implicitly assume there is one preferred frame of reference. Talk about not getting the point!

Generally speaking... (3, Funny)

Dan East (318230) | more than 3 years ago | (#35036472)

Typically they are something far, far away and a long time ago. At least from our perspective that is.

Depends on model year (5, Insightful)

boristdog (133725) | more than 3 years ago | (#35036554)

Your older Galaxies had more limited trim packages and slightly smaller engines. After 1969 the engines became larger overall and were available in a wider array of trim.

The two-door convertible with a 400 cu. inch engine would be my choice.

Should NOT be confused with an Impala.

I hope that helps.

Re:Depends on model year (1)

mcmonkey (96054) | more than 3 years ago | (#35036708)

I hope that helps.

Danm. I blew all my mods points on jokes in the Columbia thread.

Re:Depends on model year (0)

Anonymous Coward | more than 3 years ago | (#35036982)

If cost wasn't a consideration, I'd go with a '63 with a 427.

I think you'll find... (0)

Anonymous Coward | more than 3 years ago | (#35036596)

...that the universe pretty much covers everything.

It's a car! (0)

oldmac31310 (1845668) | more than 3 years ago | (#35036672)

No need for an analogy.

Re:It's a car! (1)

ocdscouter (1922930) | more than 3 years ago | (#35037174)

No need for an analogy.

That's like saying "It's a Blonde! No need for a joke!"

Supermassive Black Holes? (2)

bill_mcgonigle (4333) | more than 3 years ago | (#35036674)

I thought galaxies were determined by the presence of a supermassive black hole as its primary gravitational organizer ... but the paper doesn't even contain the word 'black'. Globular clusters sometimes have medium-mass black holes, but no supermassive ones.

Is my knowledge rusty?

Re:Supermassive Black Holes? (2)

buchner.johannes (1139593) | more than 3 years ago | (#35036934)

I thought galaxies were determined by the presence of a supermassive black hole as its primary gravitational organizer ... but the paper doesn't even contain the word 'black'. Globular clusters sometimes have medium-mass black holes, but no supermassive ones.

Is my knowledge rusty?

Not even rusty, this has never been the case. Only in the last decade it became known that black holes are in the center of most galaxies. Also, the black hole is pretty irrelevant* to the galaxy as a whole, except for the few surrounding stars, it is not the "primary gravitational organizer", it just happens that in the center, so much mass accumulates that photons can't escape. That's all.

*milky way galaxy number of stars = 3e11, black hole mass = 3.7 million stellar masses

Re:Supermassive Black Holes? (4, Interesting)

scharkalvin (72228) | more than 3 years ago | (#35037162)

Actually the formation of a black hole in the galaxy center may be the norm for galaxy formation. In fact, it may be a requirement to separate a true galaxy from just a cluster of stars. A true galaxy forms when a huge collection of gas condenses into groups of stars. A young galaxy forms a massive black hole at the center where the collection of gas is the densest. Then the galaxy goes through a Qusar phase where it emits two jets of energy formed by the accretion of matter into the black hole. Once all the nearby matter has been accreted into the black hole the Qusar shuts down.

Re:Supermassive Black Holes? (1)

Brandonski (605979) | more than 3 years ago | (#35037440)

The stars, planets, and other stuff (soylent green) are merely food.

Doesn't matter (4, Interesting)

crow (16139) | more than 3 years ago | (#35036676)

How you define "planet" or "galaxy" is very much in the nineteenth century scientific mindset of categorizing everything. Haven't we moved beyond that? Names and categories are useful as a way of generalizing a set of characteristics, but if you don't like a given definition, make up a new term for the set of characteristics that you want to generalize about.

Language is not scientific, and it never will be. We can have starfish that aren't fish and koala bears that aren't bears, and that's just fine. Scientists need to be concerned about how things work, not what they're called.

Re:Doesn't matter (1)

Anonymous Coward | more than 3 years ago | (#35037258)

Trouble is, if terms are imprecise then having a discussion becomes difficult as two people might have alternate definitions of a word. They then could actually agree in principle, but argue endlessly because they think that a word means something different than the other person thinks it means.

Example: Electric current is defined as the flow of positive charge. If half the world defined it the other way (with no natural boundary between these two groups), then the amount of things that got wired up improperly due to mis-communication would kill a great many people.

This is why we have dictionaries, to reference what the larger populace thinks a word means. Yes language is arbitrary, but without (some degree of) agreement it is completely worthless.

Fact: (-1)

Anonymous Coward | more than 3 years ago | (#35036722)

It's gayer than shit on a winkie-stick.

While we're at it... (1)

SethThresher (1958152) | more than 3 years ago | (#35036728)

You know, many other terms don't have hard and fast definitions. What exactly is a "point", mathematically speaking?

Re:While we're at it... (1)

Nadaka (224565) | more than 3 years ago | (#35036894)

Math has advanced slightly since Euclids. A point does have a hard and fast definition. It is a a location in space that can be defined exclusively by its coordinates. It has no dimension and therefore no surface and no volume.

Use the Carl Sagan Scale (4, Interesting)

jameskojiro (705701) | more than 3 years ago | (#35036740)

Trillions and Trillions of Stars = Super Galaxy

Billions and Billions of Stars = Galaxy

Million and Millions of Stars = Dwarf Galaxy

Thousands and Thousands of Stars = Stellar Cluster

Hundreds and Hundreds of Stars = Dwarf Stellar Cluster

Tens and Tens of Stars = Who gives a shit...

Re:Use the Carl Sagan Scale (0)

Anonymous Coward | more than 3 years ago | (#35037088)

Thousands and Thousands of stars = Hollywood
Hundreds and Hundreds of stars = New York
Tens and Tens of stars = Minneapolis

Re:Use the Carl Sagan Scale (1)

arth1 (260657) | more than 3 years ago | (#35037216)

Pfft. By that measure, the universe is a galaxy.

Re:Use the Carl Sagan Scale (0)

Anonymous Coward | more than 3 years ago | (#35037428)

Pfft. By that measure, the universe is a galaxy.

You mean Super Galaxy.

Re:Use the Carl Sagan Scale (0)

Anonymous Coward | more than 3 years ago | (#35037526)

And the solar system is a who gives a shit.

Re:Use the Carl Sagan Scale (0)

Anonymous Coward | more than 3 years ago | (#35037556)

Yep. The universe is just a Super Duper Galaxy.

Re:Use the Carl Sagan Scale (0)

Anonymous Coward | more than 3 years ago | (#35037356)

Why why do do you you have have to to repeat repeat all all those those words words??

You you look look silly silly.

Re:Use the Carl Sagan Scale (0)

Anonymous Coward | more than 3 years ago | (#35037510)

Your Mom = Mega Galaxy

Black hole (1)

gurps_npc (621217) | more than 3 years ago | (#35036800)

In my opinion, w galaxy should be a group of at least 1,000 stars orbiting one or more black holes

Amended (1)

rsborg (111459) | more than 3 years ago | (#35037340)

In my opinion, w galaxy should be a group of at least 1,000 stars orbiting one or more black holes

I think your definition fits our current known facts [wikipedia.org] succinctly.

A more important question is whether the definition should extend to say that the galaxy is the simply the accretion disk that forms around the black hole center.

Furthermore, star count could play a part in naming in the range cluster->dwarf galaxy->galaxy.

Amateur Opinion (1)

daemonburrito (1026186) | more than 3 years ago | (#35036840)

IANAAP, but I was up late last night thinking about this one (coincidentally).

My vote: SMBh and dark matter separates GCs from galaxies nicely. However, I think that large numbers of extant stars should not be required; ie, dark matter galaxies are galaxies. In this epoch, at least.

Would a rose, by any other name (1)

Vornzog (409419) | more than 3 years ago | (#35036888)

Still smell as sweet?

Naming and labeling things in science is as old as science itself. Often, though, as our understanding changes, so to must the old naming scheme. Usually the knowledge change becomes obvious in the scientific community - the facts are the facts, after all.

What causes all of the consternation is almost always semantics about the classification.

If there is a clear-cut scientific definition, go ahead and assign names and classifications.

Too often, though, there is no clear-cut definition, the labels don't correspond directly to the categories they are supposed to describe, and the 'formal' language fails to form a commonly accepted means of communicating your ideas, which was probably the whole point of assigning labels in the first place. SO DON'T ASSIGN THE LABELS! They don't solve the problem they are supposed to solve, they make new problems, don't bother with them.

Instead, let the language evolve as the knowledge does. I'm sure all practicing astronomers interested in galaxy scale structures share a roughly isomorphic understanding of what a galaxy is, and would agree about how to classify a pretty large subset of galaxy-ish objects. The interesting stuff - they things they actively research - will often be in the grey areas, anyway, defying classification. Don't worry about it, just go write the paper describing 'weird new not quite galaxy thing I found', and describe it as best as possible. The knowledge base will grow, the language will evolve right along with it, and we won't have to undo some silly bit of formalism the next time someone finds something that defies description.

Re:Would a rose, by any other name (1)

Belial6 (794905) | more than 3 years ago | (#35037228)

And there is the answer. Just ad '-ish' to the end of all definitions, and the problem is solved. Who can argue that Pluto is a 'planet-ish' object. Of course it is. Really, you are mostly right. Getting hung up on which noises we should grunt out to describe a particular shade of gray isn't really that productive.

[OT] Re:Would a rose, by any other name (1)

Black Parrot (19622) | more than 3 years ago | (#35037568)

Still smell as sweet?

FWIW, I always thought that Shakespeare's observation, though technically correct, was a strange sentiment for a poet.

Parable of the Heap (0)

Anonymous Coward | more than 3 years ago | (#35036890)

Sounds like what I studied in Elementary Logic.

http://www.logicalparadoxes.info/heap/

Ostensible Definition (2)

jimmerz28 (1928616) | more than 3 years ago | (#35036896)

We have this ambiguity all the time in language, debating it might be "interesting" but is really useless.

What's a "house"? How many rooms does it have? Is it a house if it has no bathroom/basement/attic? etc.

Try the same thing with "chair".

How do you know something is a "house"? You know when you see it. Just like teaching a child you point to it; ostensibly defined.

The Most Distant Known Galaxy (1)

archer, the (887288) | more than 3 years ago | (#35036910)

Finally, someone's found my marbles!

What about a super massive black hole? (0)

Anonymous Coward | more than 3 years ago | (#35036954)

If all galaxies have them, then they are the requisite phenomenon for a galaxy. To my knowledge globular clusters and alike don't have these.

map of distant galaxies (1)

Onymous Coward (97719) | more than 3 years ago | (#35036956)

The Sloan Digital Sky Survey [wikipedia.org] is a great scan of the visible universe.

You can view it in Google Sky, NASA makes the raw data available, and you can even get a 3D crystal etching [bathsheba.com] of it.

Ask Mario. (1)

JustAnotherIdiot (1980292) | more than 3 years ago | (#35036986)

He's been through two of them, I bet he knows what a Galaxy is by now.

Let me rephrase the question (1)

gstrickler (920733) | more than 3 years ago | (#35037020)

How do you divide space? In the vacuum of space, what constitutes a clear, measurable boundary?

Geographical boundaries are often based upon some physical feature, a body of water, river, mountain, etc. Some are arbitrary, such as a line of latitude or longitude, but it's something that's pretty easy to identify and measure. As far as we know, you don't have such neat boundaries in interstellar space.

Even the concept of "gravitationally bound" isn't sufficient, as stars and planets have objects gravitationally bound to them, and clusters of stars are gravitationally bound to each other, and the stars and clusters are bound to the "galaxy", and clusters of galaxies are gravitationally bound to one another. Where does one level end and the next level begin?

Re:Let me rephrase the question (1)

nschubach (922175) | more than 3 years ago | (#35037456)

Even the concept of "gravitationally bound" isn't sufficient, as stars and planets have objects gravitationally bound to them, and clusters of stars are gravitationally bound to each other, and the stars and clusters are bound to the "galaxy", and clusters of galaxies are gravitationally bound to one another. Where does one level end and the next level begin?

That's why I prefer Bound/Unbound Satellite instead of calling Earth a planet. The Moon is bound to Earth and the Earth bound to the Sun. Galaxies can be considered Generally Bound Satellites of each other.

What is a galaxy/ (0)

Anonymous Coward | more than 3 years ago | (#35037262)

What is a galaxy? A miserable little pile of planets! But enough talk, have at you!

Wrong Galaxy (1)

kiehlster (844523) | more than 3 years ago | (#35037476)

And here I thought we were talking about Android OS fragmentation and Samsung's product line being completely doomed.

what is it? (0)

Anonymous Coward | more than 3 years ago | (#35037504)

it's that game where you control a spaceship at the bottom of the screen and you try to shoot all of the bug-looking aliens at the top of the screen.

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