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Thread: Question about visible stars

  1. #1
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    Question about visible stars

    Hi,
    I have a question about the stars we look at any night we go outside and look up. Sometimes you may see just a few stars, other times you see many depending on the where you are (in the city or in the country away from light). But what occured to me is that every star we see must be in the Milky way galaxy. Is that right? I mean, none of the stars can be in other galaxies unless the star you think you are looking at is in fact another galaxy (and as far as I am aware, there are not a lot of galaxies visible to the naked eye!). Can anyone give me an opinion?

    Thanks!

  2. #2
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    I think the vast vast majority (if not all, as you said) of stars are in the Milky Way. As for galaxies, Andromeda (M31) is visible to the naked eye on a VERY dark night away from light pollution. That's really all I know for sure, I'm sure others will know more about the star bit.

  3. #3
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    Normandy pretty much got it right, all the stars we can see with the naked eye are in our galaxy. M-31 and sometimes M-33 are the only galaxys visible to the unaided eye. But they are very faint and can only be seen on a clear, moonless night and far from any light pollution.

  4. #4
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    Don't forget the Magellanic Clouds! I'm not sure if any individual stars can be seen with the unaided eye (maybe S Doradus can?), but some of the clusters must be bright enough to be seen without any trouble. Can any of our Southern Hemisphere contributors please enlighten us!

  5. #5
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    S Doradus is not naked eye visible. It is a variable star that varies from 8.6 to 11.7 magnitude. Since S Doradus is the brightest star in the Large Magellanic Cloud, it is quite certain that (except for supernovae) any star you see without aid is part of the Milky Way.

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    That makes sense I suppose. That it of course unless we got a real treat and a distant star went supernova!

  7. #7
    Actually, Supernova 1987A in the Large Magellanic Cloud was probably the first time in a loooong time that a star in another galaxy was visible to the unaided eye.

    I believe it peaked at around Magnitude 4.5, just visible from a suburban backyard.

  8. #8
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    Hi guys, thanks for the replies. So if you think about it, a regular star (non super-nova) has to be REALLY close to us for it to be visible to the naked eye. Even the majority of stars in the Milky way are not visible except for a light 'misty' band you see if you are out in the country, away from any sources of light. I expect this is due to the fact that the further you are from a star, the less of its light will reach you due to the fact that the light spreads out as a spherical shell away from the star.

  9. #9
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    Quote Originally Posted by Ryback
    Hi guys, thanks for the replies. So if you think about it, a regular star (non super-nova) has to be REALLY close to us for it to be visible to the naked eye. Even the majority of stars in the Milky way are not visible except for a light 'misty' band you see if you are out in the country, away from any sources of light. I expect this is due to the fact that the further you are from a star, the less of its light will reach you due to the fact that the light spreads out as a spherical shell away from the star.
    Be careful in teh terms you use when referring to Stars or any astronomical ideas. A regular star could be construed as a Main sequence star whish would have to be farely lose to our solar system to see with the unaided eye. BUt some stars that are very luminous can be seen with the unaided eye and they are very far away. Beetleguese is 600 ly distant. Thats far. But it is a red giant and very luminous.

    The distant fromt eh observer to the observed affects the magnitude of teh star as well as the luminoisty of the star. A red giant and supergiants are more lumious than a main sequence star. So they can be furhter away but still be seen.

    And yes the majority of the stars itn eh milkyway are not visable to teh naked eye. I believe the most visable to teh naked eye is around 3000.
    The milkyway has millions.

    If you are interested get yoursefl a used Astronomy Text book from a books store. Make sure its for a College 101 level course. It should help.

  10. #10
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    Quote Originally Posted by SouthofHeaven

    And yes the majority of the stars itn eh milkyway are not visable to teh naked eye. I believe the most visable to teh naked eye is around 3000.
    The milkyway has millions.
    I thought it was more like tens or hundreds of billions (I've seen 60 and 600 billion both given as likely numbers)

  11. #11
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    The number of naked eye stars is about 6000.

    Current estimates of the number of stars in the Milky Way are in the range of 100 billion to 400 billion stars. There is a lot of uncertainty as to how many really small star are out there. Recently a new spectral class was discovered which is called the L-class. They are smaller and cooler than the M-class that previously was at the end of the spectral sequence.

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    Just out of curiosity, what is the most distant star that can normally be seen with the naked eye? Hipparcos 5926 (V762) in Cassiopeia is 16,308 light-years away but is magnitude 5.84. That's the furthest I know of.

  13. #13
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    What amazes me is that you can see a supernovae with the naked eye which is in another galaxy but you cannot see the galaxy itself!! That means that the supernovae is producing more light than hundreds of billions of stars put together? That is unbelievable!

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    Quote Originally Posted by Ryback
    What amazes me is that you can see a supernovae with the naked eye which is in another galaxy but you cannot see the galaxy itself!!
    If you can see the supernova with the naked eye, then the parent galaxy should be close enough to be seen with the naked eye as well. Besides galaxies in the Local Group, I don't think you'll find a galaxy in which you can see the supernova with the naked eye. But you can see them if you break out a backyard telescope.

  15. #15
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    Quote Originally Posted by dgruss23
    The number of naked eye stars is about 6000.

    .
    Is that 6000 per hemisphere in the dark or total viewable combining both hemispheres. I think i just read 3000 per hemisphere.

  16. #16
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    Quote Originally Posted by SouthofHeaven
    Quote Originally Posted by dgruss23
    The number of naked eye stars is about 6000.

    .
    Is that 6000 per hemisphere in the dark or total viewable combining both hemispheres. I think i just read 3000 per hemisphere.
    Yep ~3000 per hemisphere - although how many a person can actually see depends upon latitude. An observer at the equator should be able to see all of them.

  17. #17
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    Quote Originally Posted by Eroica
    Just out of curiosity, what is the most distant star that can normally be seen with the naked eye? Hipparcos 5926 (V762) in Cassiopeia is 16,308 light-years away but is magnitude 5.84. That's the furthest I know of.
    That beats any of the stars I know of; seems there are a lot of bright distant stars in Cassiopea, what with Kappa Cass and Rho Cass;

    mind you 16,308 ly is not likely to be exact; at that distance estimates could be as much as a thousand or more light years out, I should think. Do you have any more info on this star?

  18. #18
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    Quote Originally Posted by dgruss23
    Quote Originally Posted by SouthofHeaven
    Quote Originally Posted by dgruss23
    The number of naked eye stars is about 6000.

    .
    Is that 6000 per hemisphere in the dark or total viewable combining both hemispheres. I think i just read 3000 per hemisphere.
    Yep ~3000 per hemisphere - although how many a person can actually see depends upon latitude. An observer at the equator should be able to see all of them.
    Heh, I knew I was correct. Just different reference.

  19. #19
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    Quote Originally Posted by dgruss23
    If you can see the supernova with the naked eye, then the parent galaxy should be close enough to be seen with the naked eye as well. Besides galaxies in the Local Group, I don't think you'll find a galaxy in which you can see the supernova with the naked eye. But you can see them if you break out a backyard telescope.
    A type 1a supernova with an absolute magnitude of -19.5 would be just visible to the naked eye, mag. 6, at a distance of 4,104,097 light years.
    Using m = M + 5log(d) - 5 ( M = absolute magnitude, d is in parsecs (3.26 LY))
    You're right, the limit for naked eye visible supernova is within the local group.

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