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The satellite was launched, by an Ariane 4, on August 18 1989. The original goal was to place the satellite in a geostationary orbit above the earth, however a booster rocket failure resulted in a highly elliptical orbit from 315 to 22,300 miles altitude. Despite this difficulty, most of the scientific goals were accomplished. CommunicationsThe term communications is used in a number of disciplines: communications also known as communication studies is the academic discipline which studies communication. In geography, communications are the physical routes ( roads, rivers, canals, railways, were terminated on August 17August 17 is the 229th day of the year (230th in leap years) in the Gregorian Calendar. There are 136 days remaining. Events 1807 Robert Fulton's first American steamboat leaves New York City for Albany, New York on the Hudson River, inaugurating the firs, 19931993 is a common year starting on Friday and marked the Beginning of the International Decade to Combat Racism and Racial Discrimination (1993-2003 Events January January 1 Czechoslovakia divides. Establishment of independent Slovakia and Czech Republic..
The program was divided in two parts: the Hipparcos experiment whose goal was to measure the five astrometricAstrometry is a part of Astronomy and deals with the positions of stars and other celestial bodies, their distances and movements. Part of astrometry involves creating the cosmic distance ladder. It is one of the oldest subfields of the science, the succe parameters of some 120,000 stars to a precision of some 2 to 4 milliAn SI prefix is a prefix which can be applied to any unit of the International System of Units ( SI) to give subdivisions and multiples of that unit. As part of the SI system they are officially determined by the Bureau International des Poids et Mesures.- arcsecA second of arc or arcsecond is a unit of angular measurement which comprises one-sixtieth of an arcminute, or 1/3600 of a degree of arc or 1/1296000 ≈ 7. 7E-7 of a circle. It is the angular diameter on object of 1 unit diameter at a distance of 360 and the Tycho experiment, whose goal was the measurement of the astrometric and two-colour photometricIn astronomy, photometry is the measurement of the flux or intensity of an astronomical object's electromagnetic radiation. In physics, optics, and illuminating engineering, photometry is in general the measurement of quantities associated with light. properties of some 400,000 additional stars to a somewhat lower precision.
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 is an ongoing controversy 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 2004, the controversy remains unresolved. [1]
See Also:
See also: The Hipparcos Space Astrometry Mission
Satellites