Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: A Question On Redshift

  1. Mar 23, 2010 #1
    A redshift survey has identified a galaxy cluster for which it infers a di stance of 520 Mpc. At what redshift is this cluster observed to be? You may use H0 = 72 km s−1 Mpc−1

    Now call me old fashioned but don't i need some kind of relativistic speed to calculate the redshift, i mean i have a distance of 520Mpc (=16.12x10^21m) and the hubble constant...but im sure i need a value for how fast its travelling away from me...

    Thanks

    EDIT i think i just realised that i times its distance by Ho to get its speed as its Kms-1 Mpc-1
     
  2. jcsd
  3. Mar 23, 2010 #2
    Your edit is correct.
     
  4. Mar 23, 2010 #3

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Then as long as this speed is much less than 'c' you can just use classical redshift.
    When you get redshifts approaching (or larger than) 1 you need to take into account the expansion of the universe.
     
  5. Mar 23, 2010 #4
    yeah the Lorentz factor was 1.00... so i just used z=v/c
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook