Cepheid variable
Uncertain distances

Delta Cephei is also of particular importance as a calibrator of the Cepheid period-luminosity relation since its distance is among the most precisely established for a Cepheid, partly because it is a member of a star cluster and the availability of precise parallaxes observed by the Hubble, Hipparcos, and Gaia space telescopes. The accuracy of parallax distance measurements to Cepheid variables and other bodies within 7,500 light-years is vastly improved by comparing images from Hubble taken six months apart, from opposite points in the Earth's orbit. (Between two such observations 2 AU apart, a star at a distance of 7500 light-years = 2300 parsecs would appear to move an angle of / arc-seconds = 2 x 10 degrees, the resolution limit of the available telescopes.)
combination:repeat_prompt