Hey there! Sign in to join this conversationNew here? Join for free

redshift formula: z = change in wavelength / original wavelength (need clarification) Watch

    • Thread Starter
    Offline

    0
    ReputationRep:
    lets say wavelength = l and change in wavelength dl

    z = dl/l, where l = original wavelength

    Light from a distant galaxy has an emission line with wavelength 445nm. The line has wavelength 410nm when measured in the lab. Calculate the galaxy's redshift

    Ans: 35/310


    i thought it would be z = 35/445? why is 410nm the original wavelength?

    any help appreciated, thanks in advance
    Offline

    1
    ReputationRep:
    (Original post by the maths guy)
    lets say wavelength = l and change in wavelength dl

    z = dl/l, where l = original wavelength

    Light from a distant galaxy has an emission line with wavelength 445nm. The line has wavelength 410nm when measured in the lab. Calculate the galaxy's redshift

    Ans: 35/310


    i thought it would be z = 35/445? why is 410nm the original wavelength?

    any help appreciated, thanks in advance
    Original wavelength means the wavelength in the frame it was emitted, i.e. measured when there is no relative motion between the source and the observer. Given we are trying to infer the relative motion of the galaxy, it makes much more sense to define it this way.
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Did TEF Bronze Award affect your UCAS choices?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.