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Homework Help: What is the redshift and velocity of the galaxy relative to us

  1. Mar 14, 2007 #1
    hey everyone... so im tryna solve this problem :

    a galaxy shows an emission line at a wavelenght of 6610.2 A, which we identify as the H-alpha line in the Balmer series of Hydrogen. what is the redshift and velocity of the galaxy relative to us.

    period= 4.3 days
    magnitude= 26.25
    absolute magnitude= -3.21
    distance= 7 800 000

    okay so my main problem is trying to get planck's constant. I'm tryna use v(redshift velocity)=H0(planck's constant) * D

    OR should i use Z(redshift)= (wavelenght observed-wavelenght emitted) / wavelenght emitted

    thanks!
     
  2. jcsd
  3. Mar 14, 2007 #2

    Mentz114

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    H0 is the Hubble constant, here.
     
  4. Mar 14, 2007 #3
    yes it is ....
     
  5. Mar 14, 2007 #4

    Mentz114

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    Use
    Z(redshift)= (wavelength observed-wavelength emitted) / wavelength emitted
     
  6. Mar 14, 2007 #5
    yea but i dont have 'wavelenght emitted'... i only have wavelenght observed :S
     
  7. Mar 14, 2007 #6

    Mentz114

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    Wavelength emitted is given as

    "H-alpha line in the Balmer series of Hydrogen"

    look it up.
     
  8. Mar 14, 2007 #7
    the wavelenght is not exact... and thats not what they meant by that (i think?) cuz they gave the wavelenght and i think they just mentioned the balmer series for clarification... at a wavelenght of 6610.2 A, which we identify as the H-alpha line
     
  9. Mar 14, 2007 #8
    okay i re-did the problem and now i have these values:

    distance = 29.46 m
    M (absolute magnitude)= -3.21
    period= 4.3 days
    m(magnitude)= 26.25

    i just cant seem to find an equation WITHOUT another value for wavelenght (emitted wavelenght value_)
     
  10. Mar 14, 2007 #9

    Mentz114

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    The whole point about red-shift measurements is to get the frequency difference. The emitted frequency is different and we can measure it here on earth and compare with what we received.

    Your post #7 is just wrong.
     
    Last edited: Mar 14, 2007
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