How do we measure distances in space?
Distances with in solar system are measured by radars.Near by stars by a method called parallax.Far way stars and galaxies they use Cepheid variables or type Ia supernova s standard candles.,
Radars Radio signals travel to planet return echo time is measured and speed of Radar waves in known.
Earth travel 300 KM in its orbit in one year.This is used as base and the parallax angle is measured.measured. By using trigonometry we calculate the distance..
Cephied variable stars have a relation in their pulsation period and luminosity.So they are used as standard candles.
Red shift is measured and distance calculated.