APOD: NGC 7331 and Beyond (2011 Aug 12)

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Expand view Topic review: APOD: NGC 7331 and Beyond (2011 Aug 12)

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by alter-ego » Tue Aug 16, 2011 4:19 am

magicman wrote:you are of course correct, the original error was mine, sort of, mentally when I read size I worked in 2 dimensions and read as area, hence my original question based on inverse square of distance, which would have made it 100th not 10th. Got it straight but then the second point of equalizing distance came up and blew me off course again. Ain't language a peculiar thing?, even the computer incorrects my English spellings.
I want say that response was thoughtful and gracious. Language is amazingly subtle sometimes and written language today can be easily misinterpreted in this fast-pace, quick-response world. You are certainly right about that. This is often an underlying concern of mine. Did I read that right?? What the hek did I just write?? There is always two sides to a story, and you did have an important point to make. And, as usual, the Devil's in the details
Thanks for your reply.

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by magicman » Mon Aug 15, 2011 5:02 pm

you are of course correct, the original error was mine, sort of, mentally when I read size I worked in 2 dimensions and read as area, hence my original question based on inverse square of distance, which would have made it 100th not 10th. Got it straight but then the second point of equalizing distance came up and blew me off course again. Ain't language a peculiar thing?, even the computer incorrects my English spellings.

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by alter-ego » Mon Aug 15, 2011 5:17 am

maicman wrote:Interestingly, I had started to do precisely that, when I remembered Arp's work, and conclude it would not prove anything. But I stand by my original statement, it was not meant facetiously, and believe my negative response was in fact a contribution to the discussion because it will, I hope, prevent the propagation of potentially fallacious statements and ensure that individuals state any assumptions they have made explicitly. In today's world of instant communication and internet, what is put in writing seems to be there virtually forever, or at least until our galaxy collides with another, we should not condone possible inaccuracy, the next reader may not know that the information is unproven.
Generally speaking, no argument with your point of how easy it is to publish false statements on the web, and the importance of asking questions (true with all media by the way). But I'm not sure what theoretical foundation(s) you have to evaluate conjectures, true or false. Regarding this APOD, you seemed to grapple onto a statement by R. Jay Gabany:
magicman wrote:see, there it is again "NGC7337, NGC7335, NGC7336 are ten times farther away and would dwarf the largest in this scene if their distances were equalized." For the original statement of one tenth size so 10 times further to be true they would have to be the same size if distance was equalised.
Had you trusted existing GR theory, and dug into the NASA data extragalactic database, some good would've come from it. Long story short, you would have realized that it is Gabany's statement about relative sizes appears plain wrong. In fact, when distances are equalized with NGC 7331, NGC 7337 and 7335 are the same size or smaller (within 20% or so), and NGC 7336 is about half the size. The point is, you posed a question about distance and angular size dependence which was wrong. Then you used Gabany's comment to criticize assumptions, or lack of, made by the APOD. When in essence, the general, simply put, APOD statements about approximate distances and angular sizes of neighboring galaxies were correct. In fact it was your objections that were founded in falsehoods, or at least you showed the desire to criticize without facts. I sincerely appreciate your points about representing truth, but unless you have some basis from which you can find the truth for youself, don't expect people to take your criticisms seriously. I apologize if you have taken offense, none is intended.

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by maicman » Sun Aug 14, 2011 10:51 pm

Interestingly, I had started to do precisely that, when I remembered Arp's work, and conclude it would not prove anything. But I stand by my original statement, it was not meant facetiously, and believe my negative response was in fact a contribution to the discussion because it will, I hope, prevent the propagation of potentially fallacious statements and ensure that individuals state any assumptions they have made explicitly. In today's world of instant communication and internet, what is put in writing seems to be there virtually forever, or at least until our galaxy collides with another, we should not condone possible inaccuracy, the next reader may not know that the information is unproven.

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by Chris Peterson » Sun Aug 14, 2011 3:37 pm

magicman wrote:Okay, now I'm getting it, in amongst all this scientific data and facts, lots of people are just making assumptions without any provable observations, not the method I was taught. Interesting that so few seem to question those assumptions.
Nobody said anything that was unreasonable, or likely deviated far from the truth. Why don't you apply a little of that scientific method yourself, and look up the redshift values for the more distant galaxies and let us all know just how far away they actually are?

You can complain, or you can add something positive to the discussion.

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by magicman » Sun Aug 14, 2011 3:21 pm

Okay, now I'm getting it, in amongst all this scientific data and facts, lots of people are just making assumptions without any provable observations, not the method I was taught. Interesting that so few seem to question those assumptions.

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by neufer » Sun Aug 14, 2011 1:21 am

NoelC wrote:
saturn2 wrote:
What there were before of zero point? ( million years before of zero point )
There was nothing.
________ King Lear Act 1, Scene 1

KING LEAR: Nothing will come of nothing: speak again.

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by NoelC » Sun Aug 14, 2011 1:13 am

saturn2 wrote: What there were before of zero point? ( million years before of zero point )
There was nothing. Time did not exist, no more than space or matter existed.

You're finding it hard to think outside the box (in this case, outside the universe) because you're inside it.

-Noel

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by Chris Peterson » Sat Aug 13, 2011 3:03 pm

magicman wrote:see, there it is again "NGC7337, NGC7335, NGC7336 are ten times farther away and would dwarf the largest in this scene if their distances were equalized." For the original statement of one tenth size so 10 times further to be true they would have to be the same size if distance was equalised.
The APOD caption assumes the more distant galaxies are about the same actual size as NGC7331, and are therefore ten times farther away (because they are 1/10 the size). R. Jay Gabany may be making a different assumption (or using different data) to assess the actual size of the background galaxies.

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by magicman » Sat Aug 13, 2011 12:58 pm

see, there it is again "NGC7337, NGC7335, NGC7336 are ten times farther away and would dwarf the largest in this scene if their distances were equalized." For the original statement of one tenth size so 10 times further to be true they would have to be the same size if distance was equalised.

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by geckzilla » Sat Aug 13, 2011 2:22 am

That's where the philosophers take over, saturn2.

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by saturn2 » Sat Aug 13, 2011 2:16 am

The scientifics calculate the age of Universe with the bottom radiation.
The Universe has 14 billon years old. Zero point the Big Bang.
But I think that the Big Bang theory has many errors.
For example, What there were before of zero point? ( million years before of zero point )

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by bystander » Fri Aug 12, 2011 11:42 pm

ExplorerAtHeart wrote:I dont see a bar.
neufer wrote:I think that Ann may have been posting from a bar.
[attachment=0]NGC7331 © Ken Crawford zoom.png[/attachment][/i]

That may be, but I think Ann was referring to the small
image just above and left of NGC 7331, see the zoom.

Also check out the description in R. Jay Gabany's
portrayal of NGC 7331: The Deer Lick Group.
The easily identifiable galaxies in this group are (left to right, from the top) NGC7340, NGC7337, NGC7335, NGC7336, NGC7331 (the largest), NGC3727 (the upper fuzzy component of the red-blue "double star" below the right edge of the largest) & NGC 7326.

NGC7337, NGC7335, NGC7336 are ten times farther away and would dwarf the largest in this scene if their distances were equalized.
Attachments
NGC 7331 Zoom (© Ken Crawford)
NGC 7331 Zoom (© Ken Crawford)

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by neufer » Fri Aug 12, 2011 9:10 pm

ExplorerAtHeart wrote:
I dont see a bar.
I think that Ann may have been posting from a bar.

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by ExplorerAtHeart » Fri Aug 12, 2011 8:53 pm

I dont see a bar.

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by alter-ego » Fri Aug 12, 2011 4:47 pm

Chris Peterson wrote:
Sam wrote:You're thinking of gravity.
Angular diameter varies with the arctangent of the distance.
Angular diameter varies linearly with distance (or an inverse linear relationship, depending on how you look at it). Double the distance, the angular extent is reduced by two. Ten times the distance, it is reduced by ten. When you're simply looking at how the angle varies with distance, the trig terms drop out.
Sam is technically correct here. However, subtended angle is nearly linear with distance for almost all astronomical objects. For subtended full angles <20º, the deviation from linearity is <1%.

Of course, the linearity principal for astronomical objects is not perfect either, GR affects this too.

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by Ann » Fri Aug 12, 2011 4:43 pm

orin stepanek wrote:
APOD Robot wrote:Image NGC 7331 and Beyond

Explanation: Big, beautiful spiral galaxy NGC 7331 is often touted as an analog to our own Milky Way.
Nice galaxy! 8-) Any galaxy that is similar to the Milky Way has to be nice. 8-)
Ooohh!! Congratulations, beyond! :D :D :D

It's a very nice APOD. I particularly like all the background galaxies. There is one that I can't remember having seen before, the faint bluish one at two o'clock. It is probably a dwarf galaxy made up of an intermediate population, or else of old metal-poor stars.

The Deer Lick Group looks very nice. Note NGC 7337, the pretty barred galaxy with thin, beautiful, well-formed arms.

As for NGC 7331 itself, note how we can clearly see that its arms seem to "end" or "open" at lower left. That is why we can be sure that it rotates clockwise, at least from this point of view.

In the more or less opposite direction from NGC 7331, you can find the famous Stephan's Quintet group. See here.

Fascinatingly, Stephan's Quintet and the Deer Lick Group have similar redshifts. These galaxies all recede from us at between 6,000 and 7,000 kilometers per second. (Well, except the biggest-looking member of Stephan's Quintet, which is a foreground dwarf galaxy.)

It is fascinating to consider that the Deer Lick Group and Stephan's Quintet may be at a similar distance from us. The galaxies appear to be similar in size, too. Comparing the Deer Lick Group with Stephan's Quintet really brings home how close together the Stephan's Quintet members really are.

What about NGC 7320, the interloper in Stephan's Quintet? Would you believe that it appears to be at about the same distance from us as NGC 7331?

So there are a whole lot of galaxies in this part of the sky, but maybe the Deer Lick Group and Stephan's Quintet form a kind of association, and maybe NGC 7320 is associated with NGC 7331!

Ann

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by tamarshall » Fri Aug 12, 2011 4:38 pm

Would it help the discussion about the size and age of the universe to say that the expansion of the universe is not constrained by the constant (speed of light) so the universe is bigger than it is older? That is the size of the universe is not the same as the age of the universe, i.e. it is bigger than approx 14 billion l.y.

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by tECH hIPPY » Fri Aug 12, 2011 4:34 pm

Thanks Chris. I think I'm beginning to see the photon!

Re: hubble

by Chris Peterson » Fri Aug 12, 2011 4:27 pm

tECH hIPPY wrote:I don't fully understand - if an object emitted light 13 billion years ago (which is just reaching us now), how could that object have gotten so far away from the origin point of the Big Bang (billions of lightyears) to the point at which we observe it (which is closer to us than its actual current position) without moving faster than light?
With respect to the physical point where the photon was emitted, that photon is moving faster than light. That just means that point is outside the observable Universe, and that we are causally disconnected from it. No rules are being broken here.

The speed of light (or more properly, c) does not constrain the rate at which two points in the Universe can move with respect to each other due to the cosmological expansion of the intervening space.
Or is that actually what the Big Bang was (FTL expansion) and therefore isn't it likely the universe is considerably larger than anything we could possibly measure?
In all likelihood most of the Universe is outside the observable Universe, and therefore unmeasurable. But that has nothing to do with this discussion of the size of the observable Universe.

Re: hubble

by tECH hIPPY » Fri Aug 12, 2011 4:21 pm

Chris Peterson wrote:
casubelli wrote:Thanks, Chris.
So, are you saying the universe then is at least 46 billion years old?
No, the Universe is 13.7 billion years old. But when you consider the size of the Universe, you need to consider that it has been expanding that entire time. So the most commonly given size for the observable Universe, based on comoving distance is 46 billion light years in radius. In other words, a photon that was emitted 13.7 billion years ago and is just reaching us came from a source which is now 46 billion light years away.
I don't fully understand - if an object emitted light 13 billion years ago (which is just reaching us now), how could that object have gotten so far away from the origin point of the Big Bang (billions of lightyears) to the point at which we observe it (which is closer to us than its actual current position) without moving faster than light? Or is that actually what the Big Bang was (FTL expansion) and therefore isn't it likely the universe is considerably larger than anything we could possibly measure?

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by saturn2 » Fri Aug 12, 2011 3:57 pm

Constellation Pegasus.
Distance from Earth to NGC 7331, 50 million light- years.
NGC 7331 and Our Milky Way are twin galaxies.
Two galaxies very beautiful, indeed.
Messier didn´t "saw" spiral galaxy NGC 7331.

Re: hubble

by Chris Peterson » Fri Aug 12, 2011 3:25 pm

casubelli wrote:Thanks, Chris.
So, are you saying the universe then is at least 46 billion years old?
No, the Universe is 13.7 billion years old. But when you consider the size of the Universe, you need to consider that it has been expanding that entire time. So the most commonly given size for the observable Universe, based on comoving distance is 46 billion light years in radius. In other words, a photon that was emitted 13.7 billion years ago and is just reaching us came from a source which is now 46 billion light years away.

hubble

by casubelli » Fri Aug 12, 2011 3:09 pm

Thanks, Chris.
So, are you saying the universe then is at least 46 billion years old?

Re: APOD: NGC 7331 and Beyond (2011 Aug 12)

by Chris Peterson » Fri Aug 12, 2011 1:59 pm

casubelli wrote:This picture makes me want to say: sorry folks, the universe is bigger than 14 billion light years across.
The observable universe is about 93 billion light years across, so the most distant objects we can see are about 46 billion light years away. However, this image doesn't come close to going deep enough to see any objects more than a fraction of that distance.

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