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The atmosphere in our galaxy

  1. May 20, 2004 #1
    Would you please tell me what is in there ? I mean what substances are existing ? Where can i find out some information about this ?

    Thank you very much,
  2. jcsd
  3. May 20, 2004 #2


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    Can you clarify your question? Do you mean Earth's atmosphere? Or do you mean what substances are present in the galaxy in general? Or our solar system? Or something else?

    In general, the "galaxy" - - which includes hundreds of billions of stars, etc. - - is mostly empty space (no atmosphere at all) except for a few atoms of hydrogen scattered about.
  4. May 20, 2004 #3
    Oh yes, i am so sorry, i am just really absolutely ignorant about this, that is why I didn't know how to say about what I would like to know...Honestly, i don't know..

    Thanks for your help.
    That is what i would like to know, and from what you explained, that means there is only hydrogens and no other atoms ?
    If there is any object flying in space, there will be no frictions or if any, they will be very small, right ?

    Thank you very much
  5. May 23, 2004 #4


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    The ISM (inter-stellar medium) is, as Phobos said, pretty close to a vaccuum. In fact, it's mostly a better vaccuum than we can create here on Earth. :surprise:

    However, it's not a total vaccuum, rather (for the most part) a very thin plasma. But then, looking more closely, it's actually a plasma with an enormous variation in density, even though all of it is still a very good vaccuum! :eek:

    When I return to the world of decent internet connections (about 10 days), if folk are still interested, I'll post a few links (though an hour's search with Google will probably give you much of what I'd post anyway).

    The composition of the plasma? Mostly hydrogen, some helium, and ~<a few % of all other elements.

    Interestingly, the ISM also has a 'dust' component, made up of fine grains, of varying sizes. A small %-age of the meteorites that you see (mostly the very faint ones) are interstellar dust grains; it may be that the Stardust mission has captured a few too; we'll know in a few years' time.
  6. May 23, 2004 #5
    Okay, Thank you very much and much more if you are willing to give me an answer to Where are your links ?...:sm:
    Last edited: May 26, 2004
  7. May 24, 2004 #6


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    No problem - - We like explaining this stuff. :smile:

    When the universe first formed (roughly speaking), about 75% of all matter was hydrogen. The rest was nearly all helium and a tiny bit of lithium. So that is what you would expect to find a scattering of in empty space.

    Gravity pulled together some of the denser clouds of this hydrogen-helium and formed stars. Stars jammed those atoms together (fusion) to form the heavier elements. Large stars "died" as supernova explosions which sent those heavier atoms (and created some even heavier atoms) out into space. Gravity then made new generations of stars, planets, etc.

    But nearly everywhere, atoms are very thinly spread such that "outer space" is empty...a vacuum...with just a few atoms here and there.

    Right. Essentially no friction. Take for example, the Earth going around the sun for billions of years and still going strong.

    As Nereid said, there is also some dust here and there (e.g., heavier elements that have yet to accumulate into something larger...or dust blown off comets, etc.). That is not much of a friction factor either unless you design a spacecraft that starts getting close to the speed of light...then those tiny collisions get very energetic & hazardous to space travel.
  8. May 26, 2004 #7
    In the galaxy, the hydrogen sometimes groups in certain "clouds", 3 of the most notorious are the following
    -HI regions: They are clouds of neutral hydrogen,the hydrogen is in form of atoms
    -HII regions: Also known as emission nebulae. Composed of ionized hydrogen. For example the Pelican nebula
    -Molecular clouds: Hydrogen forming molecules
  9. May 26, 2004 #8


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    In a recent scientific american they discussed the fact that there are clouds of hydrogen entering our galaxy from intergalactic space.
  10. May 26, 2004 #9
    Oh well, it is very nice of you to do that for me....I read all of what you tried to explain, Thanks alot,

    Again, Thanks Meteor and Mee a lot, also. <<<smile>>>
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