Are you comparing your naked eye observation of Milky Way with a naked eye observation of NGC891? Why make a conclusion based on different observation methods? Why subject yourself to such obvious bias?BDanielMayfield wrote:Thanks for that picture Geckzilla, which, naturally and unavoidably, is taken from the inside the Milky Way, and not about 30 million lys away as was today’s subject. But I still suspect that our galaxy has a more pronounced bulge than NGC 891 does. I come at this opinion merely from the naked eye impression I’ve gotten by looking toward the center of our galaxy.
APOD: NGC 891 Edge On (2013 Oct 11)
- geckzilla
- Ocular Digitator
- Posts: 9180
- Joined: Wed Sep 12, 2007 12:42 pm
- Location: Modesto, CA
- Contact:
Re: APOD: NGC 891 Edge On (2013 Oct 11)
Just call me "geck" because "zilla" is like a last name.
Re: APOD: NGC 891 Edge On (2013 Oct 11)
Nope. You'd hafta go a lot farther than that, Rob.rstevenson wrote:You're thinking of not by chance, which is, of course, a banned subject.Beyond wrote:haha, "not a chance", could mean "on purpose". No chance involved.![]()
Rob
![Yes. :yes:](./images/smilies/yes.gif)
To find the Truth, you must go Beyond.
- Chris Peterson
- Abominable Snowman
- Posts: 18459
- Joined: Wed Jan 31, 2007 11:13 pm
- Location: Guffey, Colorado, USA
- Contact:
Re: APOD: NGC 891 Edge On (2013 Oct 11)
I don't think this is at all comparable to the view we get of other galaxies. From our position, the bulge is a few tens of thousands of light years away, but a substantial amount of the rest of the Milky Way is much, much closer. So from within, the disc appears much thicker with respect to the bulge than it actually is.geckzilla wrote:That's something we have a lot of pictures of. It doesn't look much different from NGC891 to me. http://en.wikipedia.org/wiki/File:Milkyway_pan1.jpg
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory
https://www.cloudbait.com
*****************************************
Chris L Peterson
Cloudbait Observatory
https://www.cloudbait.com
- rstevenson
- Quis custodiet ipsos custodes?
- Posts: 2705
- Joined: Fri Mar 28, 2008 1:24 pm
- Location: Halifax, NS, Canada
Re: APOD: NGC 891 Edge On (2013 Oct 11)
Here, from the ESO, is an artist's conception of the Milky Way as seen from outside our galaxy. Our central bulge is not quite a sphere, as you can see, as it appears that both ends of the central bar are a little more puffed out than the area along the bar. ESO calls this a "peanut shaped glowing ball of stars".
For the sake of completeness, and to save you the trip, here's NGC 891.
Rob
For the sake of completeness, and to save you the trip, here's NGC 891.
Rob
Last edited by rstevenson on Fri Oct 11, 2013 10:48 pm, edited 2 times in total.
- geckzilla
- Ocular Digitator
- Posts: 9180
- Joined: Wed Sep 12, 2007 12:42 pm
- Location: Modesto, CA
- Contact:
Re: APOD: NGC 891 Edge On (2013 Oct 11)
So you're saying the perspective effect is much greater since we are within our own galaxy. Still, it's not that hard to imagine it being thinner, especially taking that into consideration.Chris Peterson wrote:I don't think this is at all comparable to the view we get of other galaxies. From our position, the bulge is a few tens of thousands of light years away, but a substantial amount of the rest of the Milky Way is much, much closer. So from within, the disc appears much thicker with respect to the bulge than it actually is.geckzilla wrote:That's something we have a lot of pictures of. It doesn't look much different from NGC891 to me. http://en.wikipedia.org/wiki/File:Milkyway_pan1.jpg
Just call me "geck" because "zilla" is like a last name.
-
- Don't bring me down
- Posts: 2524
- Joined: Thu Aug 02, 2012 11:24 am
- AKA: Bruce
- Location: East Idaho
Re: APOD: NGC 891 Edge On (2013 Oct 11)
Not at all. I don't think it would even be possible to see NGC 891 with the naked eye.geckzilla wrote:Are you comparing your naked eye observation of Milky Way with a naked eye observation of NGC891?BDanielMayfield wrote:Thanks for that picture Geckzilla, which, naturally and unavoidably, is taken from the inside the Milky Way, and not about 30 million lys away as was today’s subject. But I still suspect that our galaxy has a more pronounced bulge than NGC 891 does. I come at this opinion merely from the naked eye impression I’ve gotten by looking toward the center of our galaxy.
I was merely stating an opinion based on information received thruogh my eyes. I've looked at the bulge of the Milky Way many times, because it is always so impressive whenever I can see it. It's so impressive a sight that I can remember what it looks like, any time I think of it, because I can see it in my minds eye. So if a recorded image of another galaxy is presented as being like the Milk Way my mind can't help but compare the two images.Why make a conclusion based on different observation methods?
It's like if someone showed you a photo of a woman and then said, "Doesn't she look like the Mona Lisa?" The image of the Mona Lisa would instantly come to your mind and you would be able to make a judgement, wouldn't you?
Why not? I just wanted to know if my impression was valid or not. Apparently, it was from what Chris and Rob have posted here. Our galaxy does have a more pronounced bulge than NGC 891.Why subject yourself to such obvious bias?
Just as zero is not equal to infinity, everything coming from nothing is illogical.
- geckzilla
- Ocular Digitator
- Posts: 9180
- Joined: Wed Sep 12, 2007 12:42 pm
- Location: Modesto, CA
- Contact:
Re: APOD: NGC 891 Edge On (2013 Oct 11)
I just don't think that you can get a good feel for the structure of the Milky Way without a camera. I wouldn't make that comparison for anything other than a low light situation. A lot is revealed that our eyes can't discern in the darkest darkness. To me it would seem if you want to make a comparison ideally you'd want to use similar exposure conditions, but that's really hard since the Milky Way is right up next to us so there's some confounding factors like Chris mentioned. Still, just about any exposure compared to any other exposure should be more similar than naked eye versus CCD captured image.
Just call me "geck" because "zilla" is like a last name.
- geckzilla
- Ocular Digitator
- Posts: 9180
- Joined: Wed Sep 12, 2007 12:42 pm
- Location: Modesto, CA
- Contact:
Re: APOD: NGC 891 Edge On (2013 Oct 11)
I'd make the argument that the bulge was emphasized to illustrate the shape of the peanut for this image. Of course, the only evidence I have is more pictures of the Milky Way from within showing an absence of such an obvious double bulge. That, and the conspicuous absence of such strong features noted in other galaxies. NGC 4565 was the closest I could find to a real example of such a structure and I now realize that the Milky Way depiction is rotated in such a way to make it appear like a peanut. It's probably time to stop arguing about this since the bulge becomes more or less pronounced depending on viewing angle. Apparently we could send probes out and get data back from them a few million years later and get two different results supporting either opinion depending on which way they head out.rstevenson wrote:![]()
Just call me "geck" because "zilla" is like a last name.
- rstevenson
- Quis custodiet ipsos custodes?
- Posts: 2705
- Joined: Fri Mar 28, 2008 1:24 pm
- Location: Halifax, NS, Canada
Re: APOD: NGC 891 Edge On (2013 Oct 11)
The image of the Milky Way was from this Asterisk post of Sept. 13 this year. The Milky Way really does have a peanut shaped central bulge, whether or not the artist emphasized it. A viewer in another galaxy would be able to see the peanut if they were aligned for a side view, or not if they were aligned with the end view.
Rob
Rob
- geckzilla
- Ocular Digitator
- Posts: 9180
- Joined: Wed Sep 12, 2007 12:42 pm
- Location: Modesto, CA
- Contact:
Re: APOD: NGC 891 Edge On (2013 Oct 11)
Considering the discussion was about how pronounced the bulge is, it is important to note if an artist emphasized something about it for illustrative purposes, isn't it?
Just call me "geck" because "zilla" is like a last name.
- Chris Peterson
- Abominable Snowman
- Posts: 18459
- Joined: Wed Jan 31, 2007 11:13 pm
- Location: Guffey, Colorado, USA
- Contact:
Re: APOD: NGC 891 Edge On (2013 Oct 11)
Very. I find the vast majority of "artist's impressions" of astronomical phenomena to be flat out wrong or misleading. So even when I don't see something obviously wrong, I'm very skeptical about the degree to which these things actually represent reality in a meaningful way.geckzilla wrote:Considering the discussion was about how pronounced the bulge is, it is important to note if an artist emphasized something about it for illustrative purposes, isn't it?
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory
https://www.cloudbait.com
*****************************************
Chris L Peterson
Cloudbait Observatory
https://www.cloudbait.com
- neufer
- Vacationer at Tralfamadore
- Posts: 18805
- Joined: Mon Jan 21, 2008 1:57 pm
- Location: Alexandria, Virginia
Re: APOD: NGC 891 Edge On (2013 Oct 11)
![Image](http://academic.depauw.edu/aevans_web/HONR101-02/WebPages/Fall2009/Jeff/The%20Red%20Planet/Picture/santaclaus.jpg)
Chris Peterson wrote:Very. I find the vast majority of "artist's impressions" of astronomical phenomena to be flat out wrong or misleading. So even when I don't see something obviously wrong, I'm very skeptical about the degree to which these things actually represent reality in a meaningful way.geckzilla wrote:
Considering the discussion was about how pronounced the bulge is, it is important to note if an artist emphasized something about it for illustrative purposes, isn't it?
Art Neuendorffer
-
- Don't bring me down
- Posts: 2524
- Joined: Thu Aug 02, 2012 11:24 am
- AKA: Bruce
- Location: East Idaho
Re: APOD: NGC 891 Edge On (2013 Oct 11)
(Maybe I'm unwise to post this, but what the hey, I'm gona risk it.)geckzilla wrote:I just don't think that you can get a good feel for the structure of the Milky Way without a camera. I wouldn't make that comparison for anything other than a low light situation. A lot is revealed that our eyes can't discern in the darkest darkness. To me it would seem if you want to make a comparison ideally you'd want to use similar exposure conditions, but that's really hard since the Milky Way is right up next to us so there's some confounding factors like Chris mentioned. Still, just about any exposure compared to any other exposure should be more similar than naked eye versus CCD captured image.
Hello again group. I’ve been thinking for a while about this conversation and Geckzilla’s entry quoted above. I’ve been of two minds about saying anything more, because I don’t want to come off as being overly argumentative. But this conversation does demonstrate something that’s illustrative, and that is observational biases.
We all have a degree of bias in our view of things, based on our individual training and experiences. Arguments, often over trivial matters, arise when people can’t see eye to eye on something, but this is because they are looking at the issue through differing mental “filters”, if you will. Often nether party is wrong, they’re just seeing things differently.
In the case at hand here I have the admitted bias of being mainly an eyeball observer of the sky, at times from extremely dark sites, but also with the advantage of having seen many photos of other galaxies and diagrams of what the Milk Way was and is believed to look like as a whole. Therefore, when looking toward our galaxy’s core in Sagittarius and seeing how thick the Milky Way is in this direction, I came to an admittedly subjective impression that our galaxy’s bulge might be larger than that of the barely discernable (from our sideways view) bulge of NGC 891.
Geckzilla, you’re viewing this from a professional photographer’s standpoint, are you not? Of course our eyes can’t compare to the low light that cameras with long exposures can collect. But, apart from the rap around view of the sky you might see reproduced at a planetarium, one can’t (unless there’s a major blackout) see the grander of the Milky Way from New York City. I hope you don’t mind my asking, and I mean no disrespect, but have you done much observing with your own eyes from really dark locales at a time when Sagittarius is high? Maybe you have, and my inquiry is totally off base. If so my appologies in advance.
Cringing in fear of getting scorched, Bruce
Just as zero is not equal to infinity, everything coming from nothing is illogical.
Re: APOD: NGC 891 Edge On (2013 Oct 11)
I'm makin' popcorn; will share!
A closed mouth gathers no foot.
Re: APOD: NGC 891 Edge On (2013 Oct 11)
NGC 891 does appear to have a relatively small bulge, or maybe it just has a relatively flattened bulge. The latter is perhaps more likely, in which case we may suspect that NGC 891 may have a central bar.
My impression of the bulge of the Milky Way is that it is less flattened and more prominent and also more peanut-shaped than the bulge of NGC 891. I don't know if my impression is correct. But for what it's worth, I agree with BDanielMayfield.
My impression of NGC 891 is that it has a large yellow disk. It is always hard to judge the color and color distribution of a galaxy from a single photo, but in fact there exist many pictures of NGC 891 where the galaxy comes across as quite yellow. The U-B index of NGC 891 is 0.270 and the B-V index is 0.880. Its effective color indexes, which are redder, is 0.355 for the U-B index and 1.035 for the B-V index. We may compare these values with the color indexes for another famous and rather yellow-looking edge-on galaxy, NGC 4565. The total B-V index of NGC 4565 is 0.840, while its effective values are 0.525 (U-B) and 0.970 (B-V). In other words: NGC 891 and NGC 4565 are both relatively yellow galaxies, certainly reddened by their edge-on dusty appearance, but NGC 891 appears to be more dominated both by its old yellow population and its ultraviolet star formation than NGC 4565.
I suspect, although I definitely can't be certain, that the the disk of NGC 891 is yellower than the disk of the Milky Way.
Ann
My impression of the bulge of the Milky Way is that it is less flattened and more prominent and also more peanut-shaped than the bulge of NGC 891. I don't know if my impression is correct. But for what it's worth, I agree with BDanielMayfield.
My impression of NGC 891 is that it has a large yellow disk. It is always hard to judge the color and color distribution of a galaxy from a single photo, but in fact there exist many pictures of NGC 891 where the galaxy comes across as quite yellow. The U-B index of NGC 891 is 0.270 and the B-V index is 0.880. Its effective color indexes, which are redder, is 0.355 for the U-B index and 1.035 for the B-V index. We may compare these values with the color indexes for another famous and rather yellow-looking edge-on galaxy, NGC 4565. The total B-V index of NGC 4565 is 0.840, while its effective values are 0.525 (U-B) and 0.970 (B-V). In other words: NGC 891 and NGC 4565 are both relatively yellow galaxies, certainly reddened by their edge-on dusty appearance, but NGC 891 appears to be more dominated both by its old yellow population and its ultraviolet star formation than NGC 4565.
I suspect, although I definitely can't be certain, that the the disk of NGC 891 is yellower than the disk of the Milky Way.
Ann
Color Commentator
Re: APOD: NGC 891 Edge On (2013 Oct 11)
Do you deliverowlice wrote:I'm makin' popcorn; will share!
![Question :?:](./images/smilies/icon_question.gif)
![Mr. Green :mrgreen:](./images/smilies/icon_mrgreen.gif)
To find the Truth, you must go Beyond.
- geckzilla
- Ocular Digitator
- Posts: 9180
- Joined: Wed Sep 12, 2007 12:42 pm
- Location: Modesto, CA
- Contact:
Re: APOD: NGC 891 Edge On (2013 Oct 11)
I'm not a professional photographer and I haven't lived in NYC my whole life. I told you I grew up in rural Oklahoma. Prior to that, my childhood was spent on an even more rural hillside in a town called Lakeside, CA. Were they the darkest skies? Nope. Was it a long time ago? Yep. I spent a long time running around in the dark with my bare feet like a fearless little heathen child. Well, fearless until I almost stepped on a skunk. I used to think it was weird not to be able to see the Milky Way. When I first met Pat we broke down in the middle of nowhere in the middle of the night and I told him to look up and he got to see it for the first time. Anyway, I've seen it.
All that is beside the point that our eyes are piss poor at collecting photons. Our brains are really freakin' good at giving us a huge dynamic range which is superior to a camera but for low light conditions just about any camera is going to trump your eyes. Even next to other animals our eyes aren't the greatest at night.
All that is beside the point that our eyes are piss poor at collecting photons. Our brains are really freakin' good at giving us a huge dynamic range which is superior to a camera but for low light conditions just about any camera is going to trump your eyes. Even next to other animals our eyes aren't the greatest at night.
Just call me "geck" because "zilla" is like a last name.
Re: APOD: NGC 891 Edge On (2013 Oct 11)
I'm sorry, but that made me laugh out loud!!geckzilla wrote:fearless until I almost stepped on a skunk
(I still go barefoot...no skunks around here, though.)
Totally true; I have no trouble carrying popcorn! But I don't deliver, so you'll have to plop yourself down on the sofa here so I can hand you the bowl.Beyond wrote:Do you deliverAn owl of your stature shouldn't find it difficult to carry a light-weight bag of popcorn.
![Mr. Green :mrgreen:](./images/smilies/icon_mrgreen.gif)
A closed mouth gathers no foot.
- geckzilla
- Ocular Digitator
- Posts: 9180
- Joined: Wed Sep 12, 2007 12:42 pm
- Location: Modesto, CA
- Contact:
Re: APOD: NGC 891 Edge On (2013 Oct 11)
I don't understand why I am scary or how this is even possibly popcorn-worthy. I've been told I have a strong personality, though... "strong personality" being a kind way of putting it.
Just call me "geck" because "zilla" is like a last name.
Re: APOD: NGC 891 Edge On (2013 Oct 11)
Hmm... a bit of a drive, but...
To find the Truth, you must go Beyond.
-
- Don't bring me down
- Posts: 2524
- Joined: Thu Aug 02, 2012 11:24 am
- AKA: Bruce
- Location: East Idaho
Re: APOD: NGC 891 Edge On (2013 Oct 11)
Apologies from me to you are indeed in order then. Some things you had communicated to me had slipped my mind, I’ll try to explain why privately. I’m happy to again read that you haven’t been deprived of the joy of seeing the Milky Way with your own eyes. But, since you said that its been a long time ago, if you were to see it again, now that you have learned so much more about our galaxy you might come away with a slightly different thought, I suspect.geckzilla wrote:I'm not a professional photographer and I haven't lived in NYC my whole life. I told you I grew up in rural Oklahoma. Prior to that, my childhood was spent on an even more rural hillside in a town called Lakeside, CA. Were they the darkest skies? Nope. Was it a long time ago? Yep. I spent a long time running around in the dark with my bare feet like a fearless little heathen child. Well, fearless until I almost stepped on a skunk. I used to think it was weird not to be able to see the Milky Way. When I first met Pat we broke down in the middle of nowhere in the middle of the night and I told him to look up and he got to see it for the first time. Anyway, I've seen it.
I agree. And I apologize again in dust and ashes.All that is beside the point that our eyes are piss poor at collecting photons. Our brains are really freakin' good at giving us a huge dynamic range which is superior to a camera but for low light conditions just about any camera is going to trump your eyes. Even next to other animals our eyes aren't the greatest at night.
![Sad :(](./images/smilies/icon_sad.gif)
Just as zero is not equal to infinity, everything coming from nothing is illogical.
-
- Don't bring me down
- Posts: 2524
- Joined: Thu Aug 02, 2012 11:24 am
- AKA: Bruce
- Location: East Idaho
Re: APOD: NGC 891 Edge On (2013 Oct 11)
A strong personality is required when having to deal with assorted weirdoes.geckzilla wrote:I don't understand why I am scary or how this is even possibly popcorn-worthy. I've been told I have a strong personality, though... "strong personality" being a kind way of putting it.
Just as zero is not equal to infinity, everything coming from nothing is illogical.
- neufer
- Vacationer at Tralfamadore
- Posts: 18805
- Joined: Mon Jan 21, 2008 1:57 pm
- Location: Alexandria, Virginia
Re: APOD: NGC 891 Edge On (2013 Oct 11)
geckzilla wrote:
our eyes are piss poor at collecting photons. Our brains are really freakin' good at giving us a huge dynamic range which is superior to a camera but for low light conditions just about any camera is going to trump your eyes. Even next to other animals our eyes aren't the greatest at night.
http://math.ucr.edu/home/baez/physics/Quantum/see_a_photon.html wrote:
Can a Human See a Single Photon?
Original by Philip Gibbs 1996.
<<The human eye is very sensitive but can we see a single photon? The answer is that the sensors in the retina can respond to a single photon. However, neural filters only allow a signal to pass to the brain to trigger a conscious response when at least about five to nine arrive within less than 100 ms. If we could consciously see single photons we would experience too much visual "noise" in very low light, so this filter is a necessary adaptation, not a weakness.
Some people have said that single photons can be seen and quote the fact that faint flashes from radioactive materials (for example) can be seen. This is an incorrect argument. Such flashes produce a large number of photons. It is also not possible to determine sensitivity from the ability of amateur astronomers to see faint stars with the naked eye. They are limited by background light before the true limits are reached. To test visual sensitivity a more careful experiment must be performed.
The retina at the back of the human eye has two types of receptors, known as cones and rods. The cones are responsible for colour vision, but are much less sensitive to low light than the rods. In bright light the cones are active and the iris is stopped down. This is called photopic vision. When we enter a dark room, the eyes first adapt by opening up the iris to allow more light in. Over a period of about 30 minutes, there are other chemical adaptations that make the rods become sensitive to light at about a 10,000th of the level needed for the cones to work. After this time we see much better in the dark, but we have very little colour vision. This is known as scotopic vision.
The active substance in the rods is rhodopsin. A single photon can be absorbed by a single molecule that changes shape and chemically triggers a signal that is transmitted to the optic nerve. Vitamin A aldehyde also plays an essential role as a light-absorbing pigment. A symptom of vitamin A deficiency is night blindness because of the failure of scotopic vision.
It is possible to test our visual sensitivity by using a very low level light source in a dark room. The experiment was first done successfully by Hecht, Schlaer and Pirenne in 1942. They concluded that the rods can respond to a single photon during scotopic vision.
In their experiment they allowed human subjects to have 30 minutes to get used to the dark. They positioned a controlled light source 20 degrees to the left of the point on which the subject's eyes were fixed, so that the light would fall on the region of the retina with the highest concentration of rods. The light source was a disk that subtended an angle of 10 minutes of arc and emitted a faint flash of 1 millisecond to avoid too much spatial or temporal spreading of the light. The wavelength used was about 510 nm (green light). The subjects were asked to respond "yes" or "no" to say whether or not they thought they had seen a flash. The light was gradually reduced in intensity until the subjects could only guess the answer.
They found that about 90 photons had to enter the eye for a 60% success rate in responding. Since only about 10% of photons arriving at the eye actually reach the retina, this means that about 9 photons were actually required at the receptors. Since the photons would have been spread over about 350 rods, the experimenters were able to conclude statistically that the rods must be responding to single photons, even if the subjects were not able to see such photons when they arrived too infrequently.
In 1979 Baylor, Lamb and Yau were able to use toads' rods placed into electrodes to show directly that they respond to single photons.>>
http://cosmoquest.org/forum/showthread.php?108228-Photons-from-6th-magnitude-star wrote:
Q: How many visible light photons enter the eye each second from a star just barely bright enough to see?
Hornblower: I get a rough estimate of about 2,000 photons per second through fully dilated pupils (of 25 square millimeters).
StupendousMan: A good number to remember is that a star of magnitude zero produces roughly 1 million photons per second per square centimeter of collecting area in the V-band (or R-band or I-band). Since a mag 6 star is about 250 times fainter than a mag 0 star, that means a mag 6 star produces about 4,000 photons per square centimeter per second in the V-band. With Hornblower's estimate of the area of a dilated pupil, and allowing for the spectral sensitivity of the human eye, I'd say Hornblower's estimate is pretty good.
Last edited by neufer on Tue Oct 15, 2013 2:56 pm, edited 1 time in total.
Art Neuendorffer
- geckzilla
- Ocular Digitator
- Posts: 9180
- Joined: Wed Sep 12, 2007 12:42 pm
- Location: Modesto, CA
- Contact:
Re: APOD: NGC 891 Edge On (2013 Oct 11)
Fine, the brain-eye complex is piss-poor at collecting photons. ![Smile :)](./images/smilies/icon_smile.gif)
Supposedly, then, if you could hack your brain, you could use your eyes as more sensitive instruments.
![Smile :)](./images/smilies/icon_smile.gif)
Supposedly, then, if you could hack your brain, you could use your eyes as more sensitive instruments.
Just call me "geck" because "zilla" is like a last name.