For relatively nearby objects. The parallax used is the apparent angular shift of an object as the earth orbits the sun. The angle gets very small the further a

For relatively nearby objects. The parallax used is the apparent angular shift of an object as the earth orbits the sun. The angle gets very small the further an object is and observing it will depend on the resolution of your telescope. In practice we can only use this method for objects within our galaxy or in very nearby galaxies/star clusters. These measurements are used to calibrate the cosmic distance ladder[0] which lets us get distance estimates for further objects using other methods. The calibration between different methods is still a very active area of research because of the discrepancy between measurements of the Hubble constant based on this ladder compared with the cosmic microwave background radiation. [0] https://en.wikipedia.org/wiki/Cosmic_distance_ladder https://en.wikipedia.org/wiki/Cosmic_distance_ladder