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

Observation frequency

  1. Oct 9, 2015 #1
    I believe that when we say that this is radio telescope, it means that reciving frequency of it is in radio band. And also it means an observed object by that is in a particular redshift that its emission has a particular frequency that when recieves us, is in radio band. Am I right?
    For ex. We say cynus A is a radio galaxy. But it doesn't mean that it emits in radio freq. So it doesn't give us any info about physical activities happening in the galaxy, it just tells us about its distance from us.
    Sorry for my confusing question! I'm just wondering observing fre just tells us about distance?
  2. jcsd
  3. Oct 9, 2015 #2


    User Avatar
    Science Advisor

    It is true that "it doesn't mean that its emission has a particular frequency that when recieves us, is in radio band." However, the rest of what you say, in particular "it just tells us about its distance from us" seems to be assuming that what we receive as "radio band" is redshifted visible light. That is not in general true.
  4. Oct 9, 2015 #3
    Are all the radio galaxies in the (approximarely) same distance from us? And is the reciveing frequency from all of them in radio band?
    I am wondering whether the difference between a radio and x-ray galaxy is their redshift or their emission mechanism ?
  5. Oct 9, 2015 #4


    User Avatar
    Science Advisor
    Gold Member

    Can you cite where you have seen these terms "radio galaxy" and "x-ray galaxy" and such? I am not familiar with them as standard terminology, but it could be something I haven't heard until now. Also, I think this thread belongs better in the Astronomy and Astrophysics section.
  6. Oct 9, 2015 #5
    Oh, you are right! I'm sorry, I was supposed to post them in astronomy section.
    Thanks though!
  7. Oct 11, 2015 #6


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    That is an extremely standard and common term in astronomy
    in another thread earlier today I posted an example ... The Centaurus A radio galaxy


    as can be seen, it pumps out masses of EM right across the spectrum


    Last edited: Oct 11, 2015
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook