Hipparcos

Infobox Space telescope
name = Hipparcos


caption = Artist's conception of Hipparcos in space
organization = European Space Agency
major_contractors =
alt_names =
nssdc_id =
location =
orbit_type = Geostationary transfer orbit
height = 507 to 35,888 km
period =
velocity =
accel_gravity =
launch_date = 8 August 1989
launch_location =
launch_vehicle = Ariane 4
mission_length = 3.5 years
deorbit_date =
wavelength = Visible light
mass =
website =
style =
diameter = 29 cm
area =
focal_length = 1.4 m
coolant =
instrument_1_name =
instrument_1_characteristics =
instrument_2_name =
instrument_2_characteristics =
instrument_3_name =
instrument_3_characteristics =
instrument_4_name =
instrument_4_characteristics =

Hipparcos (an acronym for "High Precision Parallax Collecting Satellite") was an astrometry mission of the European Space Agency (ESA) dedicated to the measurement of stellar parallax and the proper motions of stars. The project was named in honor of Hipparchus. Ideas for such a mission dated from 1967, with the mission accepted by ESA in 1980.

Mission

The Hipparcos satellite was a product of Matra Marconi Space, Alenia Spazio and their industrial partners. The optical system had a 290 mm aperture, 1400 mm focal length folded Schmidt telescope. The expected precision of the instrument was in the range of 0.001–0.002 arcsecond. The satellite also included solar panels for power and an s-band antenna for communication. [cite conference
first = A. | last = Peraldi
title =The Hipparcos payload optics
booktitle =Technology for Space Astrophysics Conference: The Next 30 Years
pages =88-95
publisher =American Institute of Aeronautics and Astronautics
date =October 4-6, 1982 | location =Danbury, CT
url =http://adsabs.harvard.edu/abs/1982tspa.conf...88P
accessdate = 2007-06-12 ]

The satellite was launched by an Ariane 4 on 8 August 1989. The launch mass of Hipparcos was 500 kg. [cite web
author=Staff | date=June 12, 2007
url=http://sci.esa.int/science-e/www/area/index.cfm?fareaid=20
title=Hipparcos | publisher=ESA
accessdate=2007-06-12 ] The original goal was to place the satellite in a geostationary orbit above the earth, but failure of the apogee boost motor resulted in a highly elliptical geostationary transfer orbit with an altitude varying between 507 and 35,888 km . Despite this difficulty, all of the scientific goals were accomplished. Communications were terminated on 15 August 1993.

The program was divided in two parts: the "Hipparcos experiment" whose goal was to measure the five astrometric parameters of some 120,000 stars to a precision of some 2 to 4 milliarcseconds and the "Tycho experiment", whose goal was the measurement of the astrometric and two-colour photometric properties of some 400,000 additional stars to a somewhat lower precision.

Due to the built-in beam-splitter, Hipparcos continuously scanned the sky in two directions, separated by 58°. The image was split into a grid by 3,000 parallel slits, allowing the separation of the stars in the field of view to be measured to a high degree of accuracy. [cite web
last=Turon | first=Catherine | year=1997
url=http://wwwhip.obspm.fr/hipparcos/SandT/hip-SandT.html
title=From Hipparchus to Hipparcos: Measuring the Universe, One Star at a Time
publisher=Sky Publishing Corporation
accessdate=2007-06-12 ]

Results

The final Hipparcos Catalogue (120,000 stars with 1 milliarcsec level astrometry) and the final Tycho Catalogue (more than one million stars with 20-30 milliarcsec astrometry and two-colour photometry) were completed in August 1996. The catalogues were published by ESA in June 1997.

The Hipparcos and Tycho data have been used to create the Millennium Star Atlas: an all-sky atlas of one million stars to visual magnitude 11, from the Hipparcos and Tycho Catalogues and 10,000 nonstellar objects included to complement the catalogue data.

There were questions over whether Hipparcos has a systematic error of about 1 milliarcsec in at least some parts of the sky. The value determined by Hipparcos for the distance to the Pleiades is about 10% less than the value obtained by some other methods. As of 2007, the controversy remained unresolved. [cite web
last=den Hond | first=Bas | date=September 30, 2004
url=http://www.astronomy.com/asy/default.aspx?c=a&id=2496
title =Did the Pleiades "blind" Hipparcos?
publisher =Astronomy Magazine
accessdate = 2007-06-12 ] [cite journal
author=Soderblom, D. R.; Nelan, E.; Benedict, G. F.; McArthur, B.; Ramirez, I.; Spiesman, W.; Jones, B. F
title=Confirmation of Errors in Hipparcos Parallaxes from Hubble Space Telescope Fine Guidance Sensor Astrometry of the Pleiades
journal=The Astronomical Journal | year=2005
volume=129 | pages=1616–1624
accessdate=2007-06-12
doi=10.1086/427860]

See also

*Full-Sky Astrometric Mapping Explorer
*Gaia mission

References

External links

* [http://www.rssd.esa.int/Hipparcos/hipparcos.html The Hipparcos Space Astrometry Mission]
* [http://cdsweb.u-strasbg.fr/viz-bin/Cat?I/239 The Hipparcos and Tycho Catalogues]