Starship Asterisk*

by **Beyond** » Mon Jul 29, 2013 10:26 pm

ta152h0 wrote:high tech leg pulling is an art

Yes... we have one of those here.

by **ta152h0** » Mon Jul 29, 2013 6:55 pm

high tech leg pulling is an art

by **rstevenson** » Mon Jul 29, 2013 5:45 pm

Chris Peterson wrote:The pixel scale isn't important, since we can't spatially resolve stars in any other galaxy in any case. The pixel scale is only important because it defines how far apart two bright stars must be to be resolved as separate point sources. As long as we meet that condition, the only thing that determines whether we can detect individual stars in an image is the intrinsic brightness of those stars, and the S/N of the camera. Even a tiny amateur telescope can resolve supernovas (which are nothing more than very bright stellar sources) in galaxies much farther away than Hoag's Object.

Consider a typical luminous star, with an absolute magnitude of -11. Hoag's Object is 600 million ly away, or 184 million parsecs. That means from Earth, the luminous star will have an apparent magnitude of 25. That is very easily detected by Hubble, which has a limiting magnitude around 31. So I think it is completely possible that we are seeing individual stars in the sparse sections of this galaxy where luminous ones are far enough apart that they don't blend into the background.

Thanks Chris, that clarifies things greatly. My brain pixels are now much brighter, though no larger.

Rob

by **geckzilla** » Mon Jul 29, 2013 5:33 pm

neufer wrote:
geckzilla wrote:
In any case, I think that gonzo may have actually been referring to the galactic bulge as a red star. If I had realized that yesterday I could have more clearly stated that the central bulge is millions or billions of stars and not a singular entity.

"Gonzo" was pulling your leg.

Despite all of my cynicism I'm still rather gullible.

by **Sum Buddy** » Mon Jul 29, 2013 4:36 pm

geckzilla wrote:
Galaxian wrote:Friend, this cosmos is chock full of coincidences, lucky breaks and things that are downright weird. I am in it and that's extremely unprobable. If you really want a coincidence, how about a huge great rock slamming into the Ocean just when it was most needed to help the little furries grow into Hominids? Or Sol just happening to be in a quiet part of the galaxy for long enough for humans to get born? (Ooooh, anthropic principle alert.)
This cosmos is itself unlikely, or maybe it's absolutely certain. Whatever, it's certainly fun and it is decorated with some truly gorgeous special effects. Ring galaxies are among the loveliest.
If the Universe is destined to expand forever until it dies and becomes dark, wouldn't the Universe spend most of its time in that state? I mean, it could be in that state infinitely longer than it is in its living, moving, bright state. Coincidentally, we happen to exist in this tiny slice of time. That's my ultimate coincidental conundrum. (Something isn't right with it.)

Two days and 25 posts late but I still have to say it - Comedic Axiom #1: Timing is Everything. That should be proof enough that the universe has a sense of humor.

by **neufer** » Mon Jul 29, 2013 4:03 pm

geckzilla wrote:
In any case, I think that gonzo may have actually been referring to the galactic bulge as a red star. If I had realized that yesterday I could have more clearly stated that the central bulge is millions or billions of stars and not a singular entity.

"Gonzo" was pulling your leg.

by **geckzilla** » Mon Jul 29, 2013 3:59 pm

In any case, I think that gonzo may have actually been referring to the galactic bulge as a red star. If I had realized that yesterday I could have more clearly stated that the central bulge is millions or billions of stars and not a singular entity.

by **Chris Peterson** » Mon Jul 29, 2013 3:48 pm

rstevenson wrote:I suppose any of those individual pixels could be stars. So how big is a pixel in the image?

Hoag's object is about 100,000 light years across. Conveniently, this APOD shows Hoag's Object as about 1000 pixels wide, or a scale of about 1 pixel = 100 light years. (It's closer to 1100 pixels wide actually, but let's keep the math head-doable.) Our Sun is about 4.7 light seconds wide, for comparison. VY Canis Majoris, the largest star we know of, is about 1425 times larger than the Sun, or a little less than 2 light hours wide, still nowhere near large enough to be seen in this image if it were in Hoag's Object.

Note that I'm not saying we can't see stars in other galaxies using our best telescopes. Just not in this image.

The pixel scale isn't important, since we can't spatially resolve stars in any other galaxy in any case. The pixel scale is only important because it defines how far apart two bright stars must be to be resolved as separate point sources. As long as we meet that condition, the only thing that determines whether we can detect individual stars in an image is the intrinsic brightness of those stars, and the S/N of the camera. Even a tiny amateur telescope can resolve supernovas (which are nothing more than very bright stellar sources) in galaxies much farther away than Hoag's Object.

Consider a typical luminous star, with an absolute magnitude of -11. Hoag's Object is 600 million ly away, or 184 million parsecs. That means from Earth, the luminous star will have an apparent magnitude of 25. That is very easily detected by Hubble, which has a limiting magnitude around 31. So I think it is completely possible that we are seeing individual stars in the sparse sections of this galaxy where luminous ones are far enough apart that they don't blend into the background.

by **Chris Peterson** » Mon Jul 29, 2013 3:05 pm

geckzilla wrote:Some of those might be single stars. Or they might be multi-star systems. I don't understand how you can say with any certainty that any of them are single stars.

I'm not saying it with certainty. I simply suspect that some of the brighter, star-colored spots in that region are, in fact, stars. There's no reason they couldn't be. I'm not sure what the expected distribution of globular clusters is in the case of a ring galaxy like this.

Is it even possible to look at just one and make that determination? I still wonder if the dots around the central nebula are something like globular clusters or if they are massive stars. They seem blurry so I'm guessing they are clusters.

At that distance, I don't think clusters would be optically resolved as anything other than point sources, the same as stars. So geometrically, there is no way to distinguish the two. That could only be done by other methods, such as spectroscopically or photometrically. In either case, diffraction will make the objects larger than single pixels, and will make them "fuzzy".

Also, there are some single pixel anomalies that do happen across channels. I'm not saying I see any of them here but I'd have to go get the FITS files and spend a lot more time on it to try to make that argument. Usually those are stark white, though.

Right. Hot, warm, cool, and cold pixels are always present. Warm and cool pixels are usually eliminated by calibration, but hot and cold ones may not be. If they aren't taken care of by some sort of bad pixel mapping, they usually show up as either white or black dots. They can usually be distinguished from actual signal because they are only one pixel in extent. That can't be seen in JPEG images, but is usually not hard to see in the released TIFFs, and of course in the original FITS files.

by **rstevenson** » Mon Jul 29, 2013 12:17 pm

Chris Peterson wrote:... Looking at the image, it appears that quite a few individual stars within the galaxy are resolved.

I suspect not, at least not in this partcular image.

Here is a screen capture of a portion of this image, just inside the outer ring at about the 3 o'clock position, shown at 500% magnification.

I suppose any of those individual pixels could be stars. So how big is a pixel in the image?

Hoag's object is about 100,000 light years across. Conveniently, this APOD shows Hoag's Object as about 1000 pixels wide, or a scale of about 1 pixel = 100 light years. (It's closer to 1100 pixels wide actually, but let's keep the math head-doable.) Our Sun is about 4.7 light seconds wide, for comparison. VY Canis Majoris, the largest star we know of, is about 1425 times larger than the Sun, or a little less than 2 light hours wide, still nowhere near large enough to be seen in this image if it were in Hoag's Object.

Note that I'm not saying we can't see stars in other galaxies using our best telescopes. Just not in this image.

Rob

by **geckzilla** » Mon Jul 29, 2013 6:13 am

Some of those might be single stars. Or they might be multi-star systems. I don't understand how you can say with any certainty that any of them are single stars. Is it even possible to look at just one and make that determination? I still wonder if the dots around the central nebula are something like globular clusters or if they are massive stars. They seem blurry so I'm guessing they are clusters. Also, there are some single pixel anomalies that do happen across channels. I'm not saying I see any of them here but I'd have to go get the FITS files and spend a lot more time on it to try to make that argument. Usually those are stark white, though.

by **Chris Peterson** » Mon Jul 29, 2013 5:20 am

geckzilla wrote:Quite a few of them? I'm not sure which ones you mean. The central bulge of stars is probably the best place to look since the dust is cleared out but I assumed even the solitary looking ones in that were clusters of stars. When I process Hubble images I always have a hard time distinguishing the single pixel specks from noise, cosmic rays, or actual stars.

Actually, the central bulge is the worst place to look, because that's where the insufficient resolution is a problem. The place to look is where there aren't many stars- between the bulge and the ring. There are a number of star-like objects in there which I don't think are clusters.

Noise and cosmic rays can be distinguished from stars because only the latter are present in each color channel. Since the objects I'm seeing are white, yellow, or orange, they aren't single channel artifacts.

by **Ann** » Mon Jul 29, 2013 4:46 am

Chris Peterson wrote:
geckzilla wrote:The idiot astronomers have to grapple with questions of distance all the time and have come up with a few ways to make such determinations. However, any idiot also knows there aren't any single stars visible within the galaxy. It's too far away and the resolution is not fine enough.
I'm not so sure about that. Looking at the image, it appears that quite a few individual stars within the galaxy are resolved. Certainly, both Hubble and ground-based telescopes regularly resolve individual stars inside galaxies. This galaxy is only a little outside the range where Cepheid variables can be used to assess distance. In any case, resolution only determines the distance stars must be apart for them to be isolated from each other. Since this galaxy has very sparse regions (as between the core and ring), even a single bright star has a good chance of being resolved (detected).

You made me pay a lot of attention to the region between the core and the ring now, Chris. There are a number of rather faint yellow dots there, which I take to be globular clusters due to their sheer number and the uniformity of their color and brightness. There are, however, also two much brighter spots, one white at 6 o'clock, one bluish at 2 o'clock. I can't believe they are stars, since they are much brighter than the faint yellow dots that I take to be globular clusters. Are they clusters too, but younger and brighter? They do seem to be extended.

Ann

by **FLPhotoCatcher** » Mon Jul 29, 2013 3:48 am

This image of Hoag's Object is several years old - does anyone know if a higher resolution image of it exists?
What about a reprocessed image? I have seen several in the past that were of significantly higher quality than the originally released version.

by **geckzilla** » Mon Jul 29, 2013 2:59 am

Chris Peterson wrote:I'm not so sure about that. Looking at the image, it appears that quite a few individual stars within the galaxy are resolved. Certainly, both Hubble and ground-based telescopes regularly resolve individual stars inside galaxies. This galaxy is only a little outside the range where Cepheid variables can be used to assess distance. In any case, resolution only determines the distance stars must be apart for them to be isolated from each other. Since this galaxy has very sparse regions (as between the core and ring), even a single bright star has a good chance of being resolved (detected).

Quite a few of them? I'm not sure which ones you mean. The central bulge of stars is probably the best place to look since the dust is cleared out but I assumed even the solitary looking ones in that were clusters of stars. When I process Hubble images I always have a hard time distinguishing the single pixel specks from noise, cosmic rays, or actual stars.

by **Chris Peterson** » Mon Jul 29, 2013 1:23 am

neufer wrote:
Chris Peterson wrote:
gmPhil wrote:
It's fasscinating to ponder what the night sky might look like to a being on a planet orbiting a small star somewhere towards the inner edge of the outer ring....
I expect it would look very similar to our own night sky.
Wouldn't there be a noticeable sparsity of nearby stars?

Most of our nearby stars are within a few hundred ly, so I think you'd need to be very, very close to the edge to have much effect on that.

by **cbak80** » Mon Jul 29, 2013 1:10 am

Do you supose the Sombrero Galaxy would look like this if it were viewed from above or below rather than edge on?

by **neufer** » Mon Jul 29, 2013 1:10 am

Chris Peterson wrote:
gmPhil wrote:
It's fasscinating to ponder what the night sky might look like to a being on a planet orbiting a small star somewhere towards the inner edge of the outer ring....
I expect it would look very similar to our own night sky.

Wouldn't there be a noticeable sparsity of nearby stars?

by **Chris Peterson** » Sun Jul 28, 2013 11:43 pm

geckzilla wrote:The idiot astronomers have to grapple with questions of distance all the time and have come up with a few ways to make such determinations. However, any idiot also knows there aren't any single stars visible within the galaxy. It's too far away and the resolution is not fine enough.

I'm not so sure about that. Looking at the image, it appears that quite a few individual stars within the galaxy are resolved. Certainly, both Hubble and ground-based telescopes regularly resolve individual stars inside galaxies. This galaxy is only a little outside the range where Cepheid variables can be used to assess distance. In any case, resolution only determines the distance stars must be apart for them to be isolated from each other. Since this galaxy has very sparse regions (as between the core and ring), even a single bright star has a good chance of being resolved (detected).

by **Chris Peterson** » Sun Jul 28, 2013 11:30 pm

gmPhil wrote:It's fasscinating to ponder what the night sky might look like to a being on a planet orbiting a small star somewhere towards the inner edge of the outer ring....

I expect it would look very similar to our own night sky.

by **ta152h0** » Sun Jul 28, 2013 11:05 pm

This is why I stay up late, just to see what misteries the sky controller sends our way

by **Beyond** » Sun Jul 28, 2013 9:52 pm

neufer wrote: Gonzo journalism disregards the strictly edited product favored by newspaper media and strives for a more personal approach; the personality of a piece is equally as important as the event the piece is on. Use of sarcasm, humor, exaggeration, and profanity is common.

This somehow seems somewhat familiar to me, except for the profanity part. It's like I've run across examples of "Gonzo" journalism at various places in the Asterisk* at various times, but just don't really remember where and when, to be able to point any of them out. I seem to remember that a lot of them were of a good sort, but i also seem to remember not thinking of them as being "Gonzo" journalism. "Gonzo journalism" doesn't seem to be a term that "sticks" with me as a description of something. Perhaps it's more of a "City Dwellers" term?

by **Ann** » Sun Jul 28, 2013 9:18 pm

Can't resist going off topic again. But you started the "Ring" song, Art!

Click to play embedded YouTube video.

(If nothing else, this video gives you the chance to wonder at the kind of stage clothes worn by the members of ABBA. Fascinating.)

Ann

by **neufer** » Sun Jul 28, 2013 9:02 pm

http://en.wikipedia.org/wiki/Gonzo_journalism wrote:
<<Gonzo journalism is a style of journalism that is written without claims of objectivity, often including the reporter as part of the story via a first-person narrative. The word "gonzo" is believed to be first used in 1970 to describe an article by Hunter S. Thompson, who later popularized the style. The term has since been applied to other subjective artistic endeavors.

Gonzo journalism involves an approach to accuracy through the reporting of personal experiences and emotions, as compared to traditional journalism, which favors a detached style and relies on facts or quotations that can be verified by third parties. Gonzo journalism disregards the strictly edited product favored by newspaper media and strives for a more personal approach; the personality of a piece is equally as important as the event the piece is on. Use of sarcasm, humor, exaggeration, and profanity is common.

The term "gonzo" was first used in connection with Hunter S. Thompson by The Boston Globe magazine editor Bill Cardoso in 1970. He described Thompson's "The Kentucky Derby Is Decadent and Depraved", which was written for the June 1970 Scanlan's Monthly, as "pure Gonzo journalism." Cardoso claimed that "gonzo" was South Boston Irish slang describing the last man standing after an all-night drinking marathon. He also claimed that it was a corruption of the French Canadian word "gonzeaux", which means "shining path", although this is disputed.>>

by **geckzilla** » Sun Jul 28, 2013 7:54 pm

gonzo gonzales wrote:First, I have no astronomy training - I dropped AST 301 due to a personality conflict with the idiot teaching it.
But, I am considered a very good amateur photographer, so I understand "perspective" and "depth of field".
This leads me to ask myself (and you): how are you so certain that the red star is WITHIN the ring nebulae?
Could it not be that the angle from Hubble is such that the star APPEARS to be within the ring, but in actuality is many light years BEHIND (?) it? This would mean that the star is even larger than you surmise, or that the ring is smaller by X times than you previously measured.

But, kudos to you anyway, I very much enjoy the site and encourage you in your endeavors.

Ramon "gonzo" Gonzales

The idiot astronomers have to grapple with questions of distance all the time and have come up with a few ways to make such determinations. However, any idiot also knows there aren't any single stars visible within the galaxy. It's too far away and the resolution is not fine enough. Anything that appears to be a single star is actually either a foreground star from our own galaxy, some distant smudge of a galaxy, or some other large clumping of multiple stars in Hoag's object. Anyway, this idiot is unsure what "star" you are referring to, "gonzo".

Starship Asterisk*

APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Post a reply

Expand view Topic review: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)

Re: APOD: Hoags Object: A Strange Ring Galaxy (2013 Jul 28)