Tuesday, 9 December 2014

cosmology - How to find the distance between two quasars

I want to calculate the distance between two quasars of which I know the angular position and the red shift. Let Q1=(alpha1,delta1,z1) and Q2=(alpha2,delta2,z2) and suppose z2>z1.



I know how to find the angular separation theta between them by means of the angular coordinates. But how to find the comoving distance (at epoch z=0) from them ? I know how to find the comoving distance from the Earth of the two quasars, can we find the distance between them using these two distances?



A related question is to find the redshift of Q2 as seen by Q1 at the epoch when Q1 received the light emitted from Q2 .



There is some standard method to solve this problem ?

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