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Star question

  1. Apr 6, 2003 #1
    Explain how scientists are able to identify the elements in a star without sending a space probe question.

    I remember my teacher telling me that the answer was something about the spectrum, dont know what my teacher meant about it or what it means. Anyone can explain to me?
  2. jcsd
  3. Apr 6, 2003 #2
    Atoms undergo what are known as electronic transistions.
    this involves electrons moving from lower energy levels (sub-shells)
    to higher energy levels..u may have studied this.
    in order that an atom move from a lower energy level to a higher energy level some work (so to speak ) needs to be done and the atom needs to consume energy to make this transition..(in the form of light of specific wavelengths depending on the kind of transition etc.)
    now , to answer your question , the reverse also occurs.
    ie. when electrons in an atom move from higher energy levels to lower
    energy levels they give out energy in the form of light .

    The light emitted will have frequency or wavelength characteristic to that particular element and that particular transition .of course each atom can emit a range of frequencies (spectrum) because there are several energy levels .

    therefore, suppose we were to compare to frequency of sun light , we would find principally that it correlated with the frequency (ie. the range of frequencies -spectrum )emitted by hydrogen . so we can say that sun contains hydrogen , or helium for that matter.
    well it is'nt this simple...but it's the basic idea

    hope the above helps!!!
  4. Apr 6, 2003 #3

    Thx alot. I now get what my teacher means with the spectrum.
  5. Apr 7, 2003 #4
    quick question

    Since the composition of some stars changes with its life (hydrogen fusing into helium, helium into carbon) does the frequency of light emmited change with the core of the star? it would seem logical to me that it does but im not sure.

  6. Apr 7, 2003 #5
    logically , the frequency should change over time as the life cycle of the star progresses but my guess is that the changes involved are way too minimal to observe over even a thousand years ....that is why with respect to the sun the frequencies emitted seem more or less constant.
    so how do we know that stars go through the carbon phase..well , we know from stars that are very far away and have already come to their white giant stage,by studying their spectrum..and their spectra has shown evidence of carbon.
  7. Apr 8, 2003 #6

    Claude Bile

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    Helium was discovered by observing the spectral lines of the sun. The name Helium is derived from the word Helios which was what the ancient Greeks (I think) called the sun.
  8. Apr 8, 2003 #7


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    That is correct. But this is usually swamped by the effect of changes in temperature in the star. Eg. as star fuses helium, it cools greatly and glows red instead of orange/blue.

    What is important is generally not the spectrum in it's entirity, but the spectral lines(visible as black lines) on them. These correspond to the emmission/absorption spectra of various elements, and so allow our match.
  9. Apr 9, 2003 #8
    Well Ill be. I knew that temp changed its color but for whatever reason -probably because im slow sometimes - but I never put 2 and 2 together. Thanks for the info it is greatly appreciated :)

    and by the way...excellent board you guys have here!

  10. Apr 10, 2003 #9


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    Well, the exact relation between temperature and frequency of radiation is very complex. A high temperature increases the rate of radiation of energy from the surface of the object, and this affects it's frequency distribution of radiation by planck's equations.
    http://zebu.uoregon.edu/~js/glossary/planck_curve.html [Broken]
    Last edited by a moderator: May 1, 2017
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