# Thread: Distance of earliest emission from ancient galaxy

1. ## Distance of earliest emission from ancient galaxy

Is it possible to calculate from a galaxy of particular redshift, etc, how far away it was from our current location when it emitted the photon that has just been detected? say for a Z = 10.3 Galaxy how distant was it at the time of emission. And what is the name of this distance?

2. Order of Kilopi
Join Date
Nov 2002
Posts
6,235
Yep. This paper by Davis and Lineweaver does a good job of explaining some misconceptions of the redshift and recession in cosmology. But, in section A, on page 18, they go into detail about how to calculate distances and how to determine previous or even future distances between objects, as long as you know the distances, now.

3. I found this calculator that determines the distance between two redshifts, if one z =zero, then the distance to the other redshift seems to correspond to the previous separation distance... not quite sure how, though.

4. This is the calculator I use:

http://www.astro.ucla.edu/~wright/CosmoCalc.html

Put 10.3 into the box marked z, then hit the button marked "flat".

The distance you are looking for is known as the angular size or angular diameter distance.

For a galaxy with a redshift of z=10.3, the angular size distance is 860.6 Mpc or 2.8070 Gly, so that galaxy was 2.8 billion light-years away when the photons we currently detect were originally emitted.

For a simple overview of the different distance measures used in cosmology:
http://www.atlasoftheuniverse.com/redshift.html

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