Misleading lurkers with an obvious "circular reasoning" lie when it is the
cosmic distance ladder,
dad.
The science for lurkers:
This is the
cosmic distance ladder and its linear reasoning truth.
Rung 1: We use parallax to measure the distance to stars
inside this galaxy . Some of these stars are standard candles (
Cepheid variable stars).
Rung 2: Those standard candles are then used to measure distances to
other galaxies. Some of these galaxies contain standard candles such as Type 1a supernova.
Rung 3: Those standard candles allow the measurement of distances to more distant galaxies.
Each rung builds on the previous rung. We do not use
Cepheid variable stars to do parallax measurements. We do not use Type 1a supernova to measure the distances to
Cepheid variable stars or do parallax measurements. Thus "circular reasoning" is an obvious lie.
This is a basic list - there are up to 26 "rungs":
The ABC's of Distances.
Edwin Hubble famously used
Cepheid variable stars to measure the distance to galaxies and measured their redshift. That gave the Hubble–Lemaître law. Add 80 years of measurements and there is an enormous body of evidence that this law is correct. Thus it is a convention in astronomy to write the distances to galaxies as redshifts using the symbol z.
How is it possible to measure astronomical distances using the Doppler effect when the speed of light is always constant, regardless of the source and the observers motion?
.
