How do astronomers measure the distance of planet, stars, and galaxies?
Different methods are used depending upon distance.
Inside solar system radar is used to find distances.
For stars in other galaxies and far away stars the method of parallax is used to find distance. Cepheid variable stars are used as standard candles fore stars.in our galaxy.
For very far away galaxies Type 1 a supernova is used as standard candles.
Red shift is used s for measurement of expansion of universe.