Cosmological and doppler redshift

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Cosmological redshifts arise from the metric expansion of space, while Doppler shifts result from relative motion through space. Early astronomers distinguished these causes by observing the uniformity of redshifts across distant galaxies, which suggested a systematic rather than random motion. Hubble's law provided a framework for understanding the relationship between redshift and distance, indicating a universal expansion. However, quantifying the contributions of Hubble flow versus Doppler effects for individual objects remains complex. The discussion highlights the challenge of separating these mechanisms in the context of cosmic observations.
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cosmological redshifts are caused by the metric expansion of space, whereas doppler shift is a result of relative velocities through space. So before the development of the modern cosmological models, how did astronomers originally distinguish these two causes of redshifts (e.g. when they tried to verify the Hubble's law) ? Even with the use of Hubble's law and the standard cosmological model, can we tell how exactly these two mechanisms contribute to these redshifts?
 
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It was a question of appearances. It would be very strange if distant galaxies were all moving away from us at random.
 
mathman said:
It was a question of appearances. It would be very strange if distant galaxies were all moving away from us at random.

doesn't that only imply the existence of the Hubble flow? I mean how did astronomers ascertain how much of the redshift of a single object is caused by the Hubble flow and how much by doppler shift?
 

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