Variable Stars

(Section Not Complete)

The adjacent image shows Henrietta Leavitt. Her work at the Harvard College Observatory early in this century was instrumental in the cataloguing of variable stars and in the realization that Cepheid variables could be used to establish a distance scale (Ref). The following figure shows the variation in brightness, temperature, spectral class, surface velocity, and radius for the prototype Cepheid variable, delta-Cephei, as a function of the phase of the pulsation period, as does this animation.

Data for Cepheid Variables (CGI script).

Hipparchos variable star light curves.

The adjacent image shows the spiral galaxy NGC 4414, as imaged by the Hubble Space Telescope. By making careful brightness measurements of Cepheid variable stars detected in this galaxy, it was possible to determine that it lies at a distance of 19.1 parsecs (about 60 million light years) (Ref).

Shown below is a Hubble Space Telescope image of the galaxy NGC 4603 (Ref). At a distance of 108 million light years, this is the most distant galaxy in which Cepheid variables have been observed. At this great distance, careful statistical analysis is required to distinguish genuine variability from statistical fluctuations in the measured brightness.