Hipparcos

Hipparcos is a satellite that was used to make the Hipparcos catalog of 118,000 stars with unprecedented precision. The European Space Agency (ESA) launched it in 1989 and it operated until 1983. It was named for the ancient Greek astronomer Hipparchus and is also an acronym for HIgh Precision PARallax COllecting Satellite.

Hipparcos Media

• 

  Optical micrograph of part of the main modulating grid (top) and the star mapper grid (bottom). The period of the main grid is 8.2 micrometres.

• 

  Principles of the astrometric measurements. Filled circles and solid lines show three objects from one field of view (about 1° in size), and open circles and dashed lines show three objects from a distinct sky region superimposed by virtue of the large basic angle.

• 

  The path on the sky of one of the Hipparcos Catalogue objects, over a period of three years. Each straight line indicates the observed position of the star at a particular epoch: because the measurement is one-dimensional, the precise location along this position line is undetermined by the observation.

• 

  Typical accuracies of the FK5, Hipparcos, Tycho-1, and Tycho-2 Catalogues as a function of time. Tycho-1 dependencies are shown for two representative magnitudes. For Tycho-2, a typical proper motion error of 2.5 milliarc-sec applies to both bright stars (positional error at J1991.25 of 7 milliarc-sec) and faint stars (positional error at J1991.25 of 60 milliarc-sec).

• 

  Equirectangular plot of declination vs right ascension of stars brighter than apparent magnitude 5 on the Hipparcos Catalogue, coded by spectral type and apparent magnitude, relative to the modern constellations and the ecliptic

• 

  Artist's concept of the Milky Way galaxy, showing two prominent spiral arms attached to the ends of a thick central bar. Hipparcos mapped many stars in the solar neighbourhood with great accuracy, though this represents only a small fraction of stars in the galaxy.