Apparent distance to far galaxies

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SUMMARY

The discussion centers on measuring the apparent distance to galaxies that emitted light 13 billion years ago. It highlights that the light from these galaxies, observed now, appears much closer due to the expansion of the universe. Specifically, a galaxy that emitted light 2 billion years ago is approximately 1.75 billion light-years distant today. The Cosmic Microwave Background (CMB) represents the oldest light we can observe, originating from about 380,000 years after the Big Bang, translating to approximately 44 million light-years.

PREREQUISITES
  • Understanding of light-cone graphs in cosmology
  • Familiarity with the concept of redshift and cosmic expansion
  • Knowledge of the Cosmic Microwave Background (CMB)
  • Basic principles of distance measurement in astronomy
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  • Research the methodology for measuring cosmic distances using parallax
  • Explore the implications of redshift on the apparent distance of galaxies
  • Study the properties and significance of the Cosmic Microwave Background (CMB)
  • Investigate the concept of light-cone diagrams in cosmological models
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Astronomers, astrophysicists, and students of cosmology interested in understanding the dynamics of distant galaxies and the implications of cosmic expansion on distance measurements.

gptodd
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TL;DR
How far away were galaxies when they emitted the light we now see?
If we had a way to measure the apparent distance to 13billion light year galaxies (parallax or something) what would it be? The light left the source 13 billion years ago, so it would appear much closer.
I can't find an answer and I'm hoping you know.
 
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Hi, gptodd. Welcome to PF.

The proper distance at emission of all the light being received now is shown on the light-cone graph below:
1600812950738.png

Think of it as tracing all the light from all the galaxies which were emitting at different times on the x axis, and which we observe now (at the 13.8 point on the x axis). So e.g. a galaxy which emitted light 2 billion years ago (11.8 Gy after the big bang), and whose light we are just receiving, was approx 1.75 billion light years distant.
The oldest light we can see, from the CMB, would be near the left edge of the x-axis (at the ~380 thousand point, translating to approx. 44 million light-years on the y axis).
Whereas the farthest emitters emitted their light approximately 9 billion years ago, when they were less than 6 Gly distant.
 
Thank you so much!
-gptodd
 

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