Modern Developments in Parallax Measurement

Even with recent telescope technology, the smallest parallax angle measurable from Earth has been about 0.01". Only approximately 3000 stars have been observed with a reasonable degree of accuracy. In order to improve this figure, astronomers have launched a satellite designed specifically to measure the tiny angles involved to excellent accuracy. Parallaxes as small as 0.002" are possible. Named HIPPARCOS (HIgh Precision PARallax COllecting Satellite) in honour of the Greek astronomer Hipparchus , the satellite was put into orbit by the European Space Agency in 1989.

Despite one of its motors failing, Hipparcos has functioned brilliantly and is expected to give parallaxes for up to 120 000 stars. These results are expected to make valuable contributions to our understanding of the galaxy.

* Click here to learn about the history of stellar measurement

* Click here to find out how to calculate a star's distance from its parallax