How do someone calculate the wavelength of a receding object in space? Is it possible to calculate the original wavelength of a star, say, which is subjected to cosmological redshift?
if yes, how?
Looking at the answers I think I need to edit it to be more specific.
Suppose I'm observing a galaxy, I observe it's spectrum. From the doppler shift I indeed can calculate its velocity. Now say, z>6 then you can see it's not any sort of normal redshift, rather its the cosmological redshift.
Now my question is, from z value I'll get the a(expansion factor ), it's distance and hence how old the radiation is, but can I calculate its original wavelength and hence its temperature.
how do I calculate these??
 A: A pattern of Fraunhofer lines can identify atoms. The ratio of frequencies for pairs of lines from a pattern for a particular atom is independent of redshift. The ratio of a frequency of a line from a distance source compared with the known laboratory frequency is the observed redshift which has three components: (a) Doppler, (b) gravitational, and (c) cosmological. If you want more details, please ask.
A: You can use the redshift equation to find the original wavelength if you know the velocity that the star is moving away from you.

If you do not know the recession velocity you can utilize the oscillation of the star. If the star is stably oscillating there should be periods when you see a blue shift and periods where you see a red shift. By comparing the blue shift and red shift you can pull out an original wavelength. ( This will depend on the type of oscillation and our perspective to this oscillation.)
Hope that helps be warned I don't study astro physics. I am geared more towards mechanical engineering and applied physics, but I hope this helps :).
