Actually for lurkers, standard candles are valid science that "circular belief and thinking" ignorance cannot make wrong. It is a
cosmic distance ladder.
Rung 1: Measure the distance from the Sun to the Earth to get the astronomical unit.
Rung 2: Use the easily understood geometry of parallax (the movement of an object against a distant background form 2 different angles, e.g. look at your thumb with one eye against the horizon, swap eyes and it moves!). Measure the angle that a star seems to move from either side of the Earth's orbit. Use simple trigonometry and
rung 1 (the AU) to calculate the distances to stars. We currently have over a billion of these distances.
Rung 3: Notice that some stars that have measured distances from
rung 2 have periodic variations in brightness. These are the
Cepheid variables and a standard candle. Work out a relationship between the period and distances.
Rung 4: Use
rung 3 to calculate distances to galaxies. There are type 1a supernova in those galaxies. Their light curves gives another standard candle.
There are over 26 of these rungs, some of which overlap:
The ABC's of Distances