Are the stars that we see in constellations within the Milky Way galaxy?

In summary: Note the distances in the right-most column.In summary, the stars that we see in constellations within the Milky Way galaxy are within the Milky Way. It would be an interesting exercise to determine the farthest star that is part of a constellation.
  • #1

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Are the stars that we see in constellations within the Milky Way galaxy? Should I assume that they are close and within the Milky Way?
 
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  • #2
Yes, as far as I'm aware. There are naked-eye visible extra-galactic objects (the Magellanic clouds, Andromeda galaxy), but individual stars are too dim.
 
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  • #3
Ibix said:
Yes, as far as I'm aware. There are naked-eye visible extra-galactic objects (the Magellanic clouds, Andromeda galaxy), but individual stars are too dim.
Great majority of time. The brightest long term stars in Magellanic clouds are around magnitude +9, which is too dim to see. SN1987A was an easy naked eye object at +2,7, and it is a star, but these are not frequent.
 
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  • #4
FactChecker said:
Are the stars that we see in constellations within the Milky Way galaxy? Should I assume that they are close and within the Milky Way?
Yes. You actually CAN see galaxies (well, Andromeda, at least) outside of the milky way (with the naked eye) but not individual stars.
 
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  • #5
phinds said:
Yes. You actually CAN see galaxies (well, Andromeda, at least) outside of the milky way (with the naked eye) but not individual stars.
Thanks all. It sounds like it is a question of identifying the individual points of a constellation to determine if they are stars or galaxies. The stars will be within the Milky Way.
 
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  • #7
FactChecker said:
Thanks all. It sounds like it is a question of identifying the individual points of a constellation to determine if they are stars or galaxies. The stars will be within the Milky Way.
There are more options.
Omega Centauri is a naked eye object and a lettered part of the constellation. But it is neither a star nor a galaxy. It is perceptibly extended... for telescope. Ptolemy catalogues it as a star (on centaur´s back), it took Halley´s telescope to spot its nebulosity. It actually is a star cluster, in Milky Way. There are other clusters designated with star letters, such as Chi and h Persei (also in Milky Way). And more clusters under star numbers, such as 47 Tucanae (in Milky Way) and 30 Doradus (not in Milky Way).
But these do not seem to form parts of constellation figures. Andromeda herself is in northern sky and has a story, but her Nebula notoriously does not... Ptolemy makes no mention of nebula, only mentioned in 10th century Arab sources. And Doradus, Mensa and Tucana are southern sky. How far do the pictures of Goldfish and Toucan rely on the nebulosity of the Clouds, besides the stars in the foreground in Milky Way?
 
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  • #8
FactChecker said:
Thanks all. It sounds like it is a question of identifying the individual points of a constellation to determine if they are stars or galaxies. The stars will be within the Milky Way.
There are no galaxies that are included in the connect-the-points outlines of constellations. There may be others, but the only non-stellar object of which I can think that is included in a connect-the-points outline is the star-forming region M42 (Great Nebula; in our neck of the woods), which is part of Orion's sword.

https://en.wikipedia.org/wiki/Orion_Nebula
 
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  • #9
FactChecker said:
Are the stars that we see in constellations within the Milky Way galaxy? Should I assume that they are close and within the Milky Way?

Short answers: Yes and yes.

If, with the naked eye, you're looking at something [bright] in the night sky, and it looks like a "star" (i.e., a pinpoint of light), you can bet it's in the Milky Way galaxy and it's relatively close. While thousands of light-years away is possible, hundreds is more likely. Less than that is certainly possible too.

ancient_stars.png

[With mouseover: " 'The light from those millions of stars you see is probably many thousands of years old' is a rare example of laypeople substantially OVERestimating astronomical numbers."]
(Comic source: https://xkcd.com/1342/)

Here's a list of the 300 brightest stars, as seen from Earth (not sure if this list is still up to date, as stars vary in brightness somewhat, but it should suffice as a rough guide). Note the distances in the right-most column.
http://www.atlasoftheuniverse.com/stars.html
 
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  • #10
collinsmark said:
Short answers: Yes and yes.

If, with the naked eye, you're looking at something [bright] in the night sky, and it looks like a "star" (i.e., a pinpoint of light), you can bet it's in the Milky Way galaxy and it's relatively close. While thousands of light-years away is possible, hundreds is more likely. Less than that is certainly possible too.

[With mouseover: " 'The light from those millions of stars you see is probably many thousands of years old' is a rare example of laypeople substantially OVERestimating astronomical numbers."]
(Comic source: https://xkcd.com/1342/)

Here's a list of the 300 brightest stars, as seen from Earth (not sure if this list is still up to date, as stars vary in brightness somewhat, but it should suffice as a rough guide). Note the distances in the right-most column.
http://www.atlasoftheuniverse.com/stars.html
Another list, 92 brightest stars:
https://en.wikipedia.org/wiki/List_of_brightest_stars
It has the advantage of being sortable, which the atlasoftheuniverse list is not.
Out of the 92 brightest stars, I count 7 that are over 1000 ly away, the furthest is 2600 (and 2 more at 2000. Note that large distances tend to be less precise). 32 are less than 100 ly away.
 
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  • #11
snorkack said:
Another list, 92 brightest stars:
https://en.wikipedia.org/wiki/List_of_brightest_stars
It has the advantage of being sortable, which the atlasoftheuniverse list is not.
Out of the 92 brightest stars, I count 7 that are over 1000 ly away, the furthest is 2600 (and 2 more at 2000. Note that large distances tend to be less precise). 32 are less than 100 ly away.
Thanks! That reference also has a link to this (https://en.wikipedia.org/wiki/List_of_brightest_natural_objects_in_the_sky), which helps me to sort out what I can easily see, which are stars, which are galaxies, and what constellation they are in.
 
  • #12
collinsmark said:
...

Here's a list of the 300 brightest stars, as seen from Earth (not sure if this list is still up to date, as stars vary in brightness somewhat, but it should suffice as a rough guide). Note the distances in the right-most column.
http://www.atlasoftheuniverse.com/stars.html
Kind of weird how the stars on that list fit a Bell curve almost exactly.
Perhaps I'll turn that into a homework problem, as to why that is.

distribution of distances of visible stars from Earth. 2023-01-05 at 00.17.34.png

I wonder if this is how Planck got started developing his curve, sitting at home solving peculiar math problems.

I'm guessing the left side goes up like that because of increasing logarithmic volumes and the right side goes down because of the inverse square law.
Along with some distribution of star brightnesses thrown in to spice it up.
 
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  • #13
January 9, 2023 (Phys.org) Astronomers find the most distant stars in our galaxy halfway to Andromeda
https://phys.org/news/2023-01-astronomers-distant-stars-galaxy-halfway.html
Astronomers have discovered more than 200 distant variable stars known as RR Lyrae stars in the Milky Way's stellar halo. The most distant of these stars is more than a million light years from Earth, almost half the distance to our neighboring galaxy, Andromeda, which is about 2.5 million light years away.

The characteristic pulsations and brightness of RR Lyrae stars make them excellent "standard candles" for measuring galactic distances. These new observations have allowed the researchers to trace the outer limits of the Milky Way's halo.

"This study is redefining what constitutes the outer limits of our galaxy," said Raja GuhaThakurta, professor and chair of astronomy and astrophysics at UC Santa Cruz. "Our galaxy and Andromeda are both so big, there's hardly any space between the two galaxies."

Ostensibly, Andromeda and Milky Way galaxies could exchange stars.

Yuting Feng, a doctoral student working with GuhaThakurta at UCSC, led the new study and is presenting their findings in two talks at the American Astronomical Society meeting in Seattle on January 9 and 11.

According to Feng, previous modeling studies had calculated that the stellar halo should extend out to around 300 kiloparsecs or 1 million light years from the galactic center. (Astronomers measure galactic distances in kiloparsecs; one kiloparsec is equal to 3,260 light years.) The 208 RR Lyrae stars detected by Feng and his colleagues ranged in distance from about 20 to 320 kiloparsecs.
 
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  • #14
Hmmm....

RR Lyrae's are commonly found in globular clusters. So saying what galaxy they are from doesn't quite tell the story.
 
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  • #15
Vanadium 50 said:
RR Lyrae's are commonly found in globular clusters. So saying what galaxy they are from doesn't quite tell the story.
Is the underlying issue here that "which galaxy does this star belong to" is a classification problem, not a physics problem? So for edge cases like stars half way-ish between here and Andromeda it depends what (somewhat arbitrary) classification rule you apply and stuff like whether you ever count clusters as separate from a galaxy, etcetera, etcetera, while there's a stable answer for stars in our night sky under any even vaguely sensible rule.
 
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  • #16
Ibix said:
a classification problem, not a physics problem
Lots of things are like this. What is a merger and what is merely mass transfer?
 
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  • #17
As an aside, there are at least two globular clusters originally misidentified as stars, both mentioned in this thread. There is also an entire galaxy misidentified as a star, BL Lacertae,
 
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  • #18
Vanadium 50 said:
There is also an entire galaxy misidentified as a star, BL Lacertae,
Is BL Lacertae a galaxy, or a black hole?
Note that "asteroid" and "quasar" are two different spellings of "star-like". "Aster"-"oid", or "quasi"-"star".
 
  • #19
snorkack said:
Is BL Lacertae a galaxy, or a black hole?
That distinction makes no sense. It's an active galaxy, and like many galaxies has a central black hole.
 
  • #20
Well, "Sagittarius A" is a designation distinct from "Milky Way". What precisely is "Virgo A"? Is it a synonym of "M87", or is it the nucleus as disinct from the surrounding galaxy?
BL Lacertae shares the property with 3C 273 and many other quasars, that the nucleus outshines the surrounding galaxy (in case of 3C 273, by about 3 magnitudes).
 
  • #21
Honestly, I think this is a meaningless distinction you are trying to draw. The entire galaxy covers an angular extent comparable to a large star so there is little point in quibbling about parts of the galaxy.
 
  • #22
Vanadium 50 said:
Honestly, I think this is a meaningless distinction you are trying to draw. The entire galaxy covers an angular extent comparable to a large star so there is little point in quibbling about parts of the galaxy.
I see your point.

This wiki entry seems to read as if BL Lac is an entity implicitly distinct from what it refers to as its "host" galaxy - but in the context of the OP question that's a pretty moot point. As a sky object, it's a single object.
 
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  • #23
Vanadium 50 said:
Honestly, I think this is a meaningless distinction you are trying to draw. The entire galaxy covers an angular extent comparable to a large star so there is little point in quibbling about parts of the galaxy.
The biggest stars are R Doradus and Betelgeuse, around 5 centiseconds across. Which means about 1 in 4 millions. At the 280 Mpc distance of BL Lac, this makes around 70 pc. Is the galaxy really that small?
But an example about ambiguity of what you see is the Sword of Orion.
The brightest components are:
θ1 C is +5,13
θ1 A and D are +6,7, B +7,9, all of them within half a minute of C. (Other stars are below +10)
θ2 A is +5,02
θ2 B is +6,4 and C +8,2. And those are slightly more separated than the θ1 components.
θ2 A and θ1 C are bright enough that you might see them as single stars, and θ2 A is the slightly brighter of these. But since θ1 C has more companions with tighter separations, these sum up to a brighter visible spot. So what do you really see? A cluster, or the brightest star of the cluster?
 
  • #24
This is quibbling, nad IMO unhelpful to the OP.

Is there any doubt that the angular extent of BL Lac is much, much, much closer to that of R Doradus than ω Cen?
 
  • #25
OmCheeto said:
Kind of weird how the stars on that list fit a Bell curve almost exactly.
Perhaps I'll turn that into a homework problem, as to why that is.

View attachment 319817
I wonder if this is how Planck got started developing his curve, sitting at home solving peculiar math problems.

I'm guessing the left side goes up like that because of increasing logarithmic volumes and the right side goes down because of the inverse square law.
Along with some distribution of star brightnesses thrown in to spice it up.
This is a very surprising discovery, in fact I tend to think it must be a coincidence, though one hesitates to assume a lovely Gaussian is a coincidence! Generally you get a Gaussian when you mix enough independent parameters that go into how bright something looks (central limit theorem), but it's not obvious that enough independent things are being mixed. It seems like it is basically three-- the stellar luminosity, distance, and dust absorption per LY along the way. Each of those have their own distribution, but only dust absorption per LY would be likely to be distributed like a Gaussian, and it should not really matter for the closer stars.

If you neglect dust absorption, then everything else is pretty much distributed like a power law-- the distribution of stars over luminosity, the distribution of volume over distance, and how luminosity converts to a naked eye threshold with distance, are all power laws for the main-sequence stars (and the red giants have their own rules, but still that's only two sets of objects, dwarfs and giants, not really a lot of mixing there). So one expects the distribution to be a power law, or perhaps a sum of two power laws to include the red giants, until dust absorption comes into play (using ln(d) as the variable just increases the power by 1, it's still a power law). So the most natural interpretation of your result is that you start out with something like a power law, then start cutting it off at larger distance, presumably due to dust absorption. But that certainly doesn't explain the symmetric Gaussian you obtain!

Still, the possibility that the perfect Gaussian is a coincidence is further supported by the extremely good fit that is achieved, when such small number statistics should not produce such a good fit. Given the expectation of statistical variations on the order of the square root of the numbers plotted, only the central three values are anywhere near statistically significant enough to fit a curve right through them. So if you really only have three points to fit a curve through, and a Gaussian has three parameters, you can always do it. You might be skeptical of that conclusion because it does not explain why that same Gaussian fits the points out on the wings, but remember those points represent 25, 9, 3, and 1 star, so the statistical variances on those numbers are pretty large-- meaning that you should really not expect any curve that fits the central points to also fit right through those! It is an "embarrassment of riches", so I think it has to be a coincidence, given those statistics, even though it is rather amazing that it fits so well to that Gaussian.
 
  • #26
Vanadium 50 said:
This is quibbling, nad IMO unhelpful to the OP.
It is actually a point which addresses the OP: Orion´s Sword is a part of a major constellation outline the way 47 Tucanae clearly is not, and ω Centauri... is it? Yet what is θ Centauri? A star, or a star cluster? Identifying it as either is dubious.
 
  • #27
phinds said:
You actually CAN see galaxies (well, Andromeda, at least)
It's not much more than one hundred years ago that people thought that the so called Milky Way Galaxy was, in fact 'THE Galaxy'. The Andromeda Galaxy was thought to be just another Nebula (the Andromeda Nebula). It was only when the distances were measured // calculated that we discovered objects (galaxies) way outside our galaxy. Hubble's and other's work established that the distances in the universe are billions of light years; much greater than the diameter of the MW.
Big, space-born telescopes show incredible details of individual stars in distant galaxies. I find that mind boggling. We are living in a fantastic age of space observation.
 
  • #29
BWV said:
very few, if any, stars outside our galaxy cataloged by astronomers
Certainly the SN1987A progenitor was. Along with 1271 just like it in the same survey, Or maybe I should say 1271 remaining. :smile:

As far as the bell-like distribution, well, the shape needs to be generally "belly". At one end you need very bright stars to see them, and they are rare, and at the other end you need dim stars to be very close and they are rare too. (Trivia question: how many stars are visible to the naked eye and are dimmer than the sun?)

The x-axis is in magnitudes as opposed to something more reasonable like Janskies. So it's really not a normal distributiom - more like lognormal. Those show up when you have products of random numbers instead of sums, and that seems a lot more plausible.

Also, a normal distribution has 3 parameters and we only have 6 significant points. So I don't think this is surprising. More an "oh" than a "holy smokes!"
 
  • #30
Vanadium 50 said:
As far as the bell-like distribution, well, the shape needs to be generally "belly". At one end you need very bright stars to see them, and they are rare, and at the other end you need dim stars to be very close and they are rare too.
Dim stars don't need to be rare (they aren't really) to see the rise at low ##d## (why isn't this showing up as LaTeX?), they only have to not be way more common than the Sun (which indeed they aren't). For ##d## small enough that dust extinction is little issue (which does seem to be the case here), the distribution ##dN/dln(d)## with apparent brightness above some limit (in this case the limit determined by the list of brightest stars) is proportional to ##d^3 f(d^2)##, where ##f(L)## is the relative number of stars with intrinsic luminosity above ##L##, and ##d## is measured in units appropriate to the chosen brightness cutoff that defines the list. So as long as ##f## does not rise toward smaller ##L## faster than ##L^{-3/2}##, we will see a rising distribution at low ##d## due to the volume effect. (And if ##f(L)## did rise faster than that, the night sky would be chalk full of dim objects, which is your point, but that's why it doesn't require they be rare, just not super common-- for example, you'd need some 30 times the density of stars 1/10 the luminosity of the Sun to have this problem).

You make the point that the turn over in the plot could be due to a change in the ##f(L)## function where it does start to fall faster than ##L^{-3/2}##. That's probably right, the turnover is at a few hundred LY, but dust extinction should not be strong until several thousand. In fact, we can see that a lot of the dimmest stars that make this list are red giants that are about a hundred times more luminous than the Sun, and red giants don't spend a lot of time much brighter than that. So that's probably what we are seeing in the turnover of the distribution, the fact that to see stars that far away, a lot of the stars will need to be giants, and giants evolve faster as they get brighter, so they are rarely in those brighter stages that we need them to be in to see them at the largest distances in the plot.

The list also includes a smattering of massive stars, which are very bright while still on the main sequence, and in a region of steady-state star formation, there would be enough of them to keep the plotted distribution from turning over (their ##f(L)## would not be far from ##L^{-3/2}## as it happens). But our region of the Milky Way is not a place where there is steady-state star formation, since it's not inside a spiral arm, so a lot of the massive stars formed too long ago to still be on the main sequence, and that should also contribute to the turnover.

So yeah, the turnover is probably due to the rarity of very luminous stars. The Gaussian nature still seems like a coincidence, as the rising and falling parts are due to very different reasons and it really shouldn't look that symmetric or that Gaussian, and the statistics are too poor to expect that it would anyway.
Vanadium 50 said:
The x-axis is in magnitudes as opposed to something more reasonable like Janskies.
I believe the x axis is ln(distance), so the only place brightness comes into play is in the cutoff minimum apparent brightness that goes into the set of stars, which can be measured in any unit without consequence to the shape of the curve.

Vanadium 50 said:
Also, a normal distribution has 3 parameters and we only have 6 significant points. So I don't think this is surprising. More an "oh" than a "holy smokes!"
That's what I meant about the fact that there are really only 3 statistically well-quantified points, and the other 3 should have significant uncertainties so it's pretty coincidental they fit perfectly to any smooth curve, let alone a nice symmetric Gaussian. I suspect that a more complete distribution (say if it included the 10,000 brightest stars) would not be Gaussian, because the rise seems to be due to an ##f(L)## function that is less steep than ##L^{-3/2}## due to red giants, and the turnover is due to the fact that we live in a region where there has not been a lot of recent star formation, so that should not even make a symmetric curve, let alone Gaussian. So it's really a remarkable coincidence that the curve looks so perfect, given the statistics.
 
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  • #31
Vanadium 50 said:
At one end you need very bright stars to see them, and they are rare, and at the other end you need dim stars to be very close and they are rare too. (Trivia question: how many stars are visible to the naked eye and are dimmer than the sun?)
That depends on the magnitude threshold your eye and sky allow.
Adopting +6,00:
  1. ε Eridani +3,73 +6,19
  2. 61 Cygni +4,7 +7,5 (Not resolved by naked eye but combined magnitude is not commonly quoted. Simple mathematics but some taking of logarithms, so I rounded)
  3. ε Indi +4,69 +6,89
  4. τ Ceti +3,49 +5,68 the brightest of these, about nr. 280 of all stars
  5. ο2 Eridani +4,43 +5,93
  6. 70 Ophiuchi +4,00 +5,66
  7. σ Draconis +4,67 +5,87
  8. 33 Librae +5,64 +6,79
  9. 36 Ophiuchi +4,3 +6,2 (again AB combined magnitude rounded)
  10. 279 Sagittarii +5,31 +6,41
  11. e Eridani +4,26 +5,35
  12. Gliese 892 +5,57 +6,49
  13. ξ Bootis +4,7 +5,59
  14. Gliese 105 +5,79 +6,50
  15. 96 Piscium +5,74 +6,37
  16. 107 Piscium +5,24 +5,86
  17. μ Cassiopeiae +5,17 +5,78
  18. p Eridani +5,0 +6,25
  19. 61 Virginis +4,74 +5,09
  20. 41 Arae +5,55 +5,83
  21. 5 Capricorni +5,73 +6,00
  22. κ1 Ceti +4,84 +5,16
  23. 66 Centauri +4,89 +5,06
  24. 61 Ursae Majoris +5,31 +5,41
  25. 289 Hydrae +5,97 +6,06
  26. 12 Ophiuchi +5,77 +5,82
  27. Gliese 75 +5,63 +5,61
  28. α Mensae +5,09 +5,03 the dimmest lucida and the only lucida to be dimmer than Sun
  29. 54 Piscium +5,88 +5,65
  30. 11 Leonis Minoris +5,40 +5,16
  31. ζ1 Reticuli +5,52 +5,11. Note that ζ2, resolved by naked eye, is so close to Sun in brightness that sources differ on which is the brighter
  32. 85 Pegasi +5,81 +5,34
  33. ρ1 Cancri +5,96 +5,47
  34. 285 Puppis +5,95 +5,45
  35. 24 Virginis +5,54 +4,99
  36. 86 Sagittarii +5,85 +5,28
  37. 58 Eridani +5,63 +5,01
  38. π1 Ursae Majoris +5,63 +4,86
  39. ψ Serpentis +5,86 +5,03
  40. Gliese 1021 +5,80 +4,93
There is a possibility of a few more just beyond 15 pc, but likely not many.
 
  • #32
Ken G said:
So it's really a remarkable coincidence that the curve looks so perfect, given the statistics.
I think it's just a happy coincidence.
Expanding the grouping to 34 points yields a much dirtier fit.

Dirtier bell data. 2023-04-15 at 20.38.45.png

x-axis: 0.9 * ln( distance in light years )
y-axis: star count

Now if I can just figure out how to extract less than a billion data points from the Gaia database, I'll be able to make some more fancy graphs.
 
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