Statistics – Computation
Scientific paper
Oct 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995xmm..pres...22.&link_type=abstract
XMM Press Release INFO 22-1995
Statistics
Computation
Scientific paper
The Hipparcos project was recommended by the leading scientific advisors to the European Space Agency back in 1980. Its sole objective was to tackle he most rudimentary yet one of the trickiest questions in the whole of astronomy : in what directions do the various stars comprising our Milky Way lie ? How far away are hey ? And how fast are they moving through the enormous expanses of space ?
One million million bits of data were acquired by the satellite during its thee-year operational lifetime. After a flawless launch by an Ariane 4 rocket in August 1989, he boost motor on he satellite failed to ignite, and the satellite was destined to conduct its scientific observations from he wrong orbit. Ingenious ESA and industry engineers, assisted by scientists, a NASA ground- station, and strong political and scientific support, resolutely declined to forfeit he mission, and designed ever more complex control systems to keep he data flowing. In this way, contact between he satellite and the European Space Operations Centre (ESOC) - and a relentless stream of high quality scientific data - was maintained until August 1993. And since shortly after launch, number-crunching computers across Europe have been digesting he huge data stream, and piecing together the information in the largest computational jig-saw in the history of astronomy.
For thousands of years, astronomers have defined the sky's shape as an imaginary celestial sphere, with the direction to any single star given by angles like he longitude and latitude used by geographers. But the stars move, and the Earth is a moving, wobbling platform. Its atmosphere makes star images shimmer, and its gravity causes telescopes on its surface to droop as they scan the heavens. Observatories on the ground are limited to studying parts of he sky, and trying to piece together a celestial survey from the ground has run into insurmountable problems. The ingenuity of scientist involved in positional astronomy, or astrometry, led them, almost 30 years ago, to propose carrying out these observations from the relatively benign environment of space.
Hipparcos is, by present standards, a medium-sized satellite, with a 30 cm telescope sensing simply ordinary light. But it has been described as the most imaginative in the short history of space astronomy. This foresight has been amply repaid. In the long history of stargazing it ranks with the surveys by Hipparchus the Greek in the 2nd Century BC and by Tichy Brahe the Dane in the 16th Century AD, both of which transformed human perceptions of the Universe. Positions derived from the Hipparcos satellite are better than a millionth of a degree, and newly a thousand times more accurate than star positions routinely determined from he ground. This accuracy makes it possible to measure directly the distances to the stars. While it took 250 years between astronomers first setting out on the exacting task of measuring the distance to a star, and a stellar distance being measured for the first time, ESA's Hipparcos mission has revolutionised this long, painstaking, and fundamental task by measuring accurate distances and movements of more than one hundred thousand.
The measurement concept involved he satellite triangulating its way between he stars all wound the sky, building up a celestial map in much the same way as land surveyors use triangulation between hill-tops to measure distances accurately. Only the angles involved are much smaller : the accuracy that has been achieved with the Hipparcos Catalogue is such that he two edges of a coin, viewed from he other side of the Atlantic Ocean, could be distinguished. The results from Hipparcos will deliver scientists with long-awaited details of our place in he Milky Way Galaxy. Most of he stars visible to the naked eye are, to a large extent, companions of the Sun, in a great orbital march around the centre of the Galaxy, a journey so long that it takes individual stars 250 million years to complete, in itself a time so inconceivably long that only a few revolutions of our Galaxy have been completed since its formation - dinosaurs ruling our planet less than one quarter of a revolution ago. Hipparcos has measured the details of this cosmic procession, and will allow a clear disentangling of the motions of the individual stars ; which lie relatively close to our Sun? which are massive highly-luminous stars at great distances from it ? which are moving in an orbit close to our Sun's ? and which are racing away from it hundreds of times faster than the speed of sound ?
After eight years in the planning and construction stages, Matra Marconi Space, Alenia Spazio, and their 30 or so high-technology industrial partners delivered the Hipparcos satellite to ESA, on schedule and within cost. With the exception of its boost motor, the satellite and all its instruments functioned flawlessly, and indeed surpassed all expectations - in spite of he harsh environment that it was subjected to in its unintended orbit. The Matra Marconi Space Project Manager, Michel Bouffard, expressed his own satisfaction with the Hipparcos Catalogue completion, and remarked hat "the Hipparcos project is definitely one of the best examples of intense and fruitful collaboration between ESA, industry and scientist".
A few more months work will be required before the Hipparcos Catalogue, and its companion Tycho Catalogue of more than a million stars, can be released by the European Space Agency. "We have to fit into the completed catalogue all of the double stars, and all of the magnitude measurements, that have been acquired", explained Dr Michael Perryman, ESA's scientist working with the European scientific teams. "But the schedule for this has now been drawn up " he added. Scientists who formulated parts of the satellite's observing programme, and who were involved in the analysis of the satellite data, will be given the first opportunity to try to understand what the data mean, from an astronomical perspective, when the results are delivered to them at the end of March 1996. The final product of the Hipparcos mission, a monumental 14-volume catalogue, with page upon page of astronomical results of unprecedented accuracy, will be published by ESA and the scientific teams at the end of March 1997.
The four leaders of he European scientific teams, who have been involved in the project since its earliest days, announced hat he Hipparcos and Tycho Catalogues have passed all he test that they have been able to devise to assess he quality of he data. Professor Jean Kovalevsky (Observatoire de la Cote d'Azur, Grasse, France), Dr Lennart Lindegren (Lund Observatory, Sweden), Professor Erik Hog (Copenhagen Observatory, Denmark), and Dr Catherine Turon (Observatoire de Paris-Meudon), and other scientific representatives from the ESA member states, are delighted with he latest developments. "There will be thousands of direct and indirect users of the Hipparcos results over the coming years", said Catherine Turon who lead the team responsible for putting together the satellite's observing programme, "and they will not only have access to a magnificent catalogue, but one which has been finalised somewhat more rapidly than our expectations before launch ". Some ten thousand known double star systems have been observed by Hipparcos, and nearly ten thousand more have been discovered for the first time. In these binary systems, two stars orbit around each other, and Hipparcos promises to provide measurements of the masses of he stars in such systems, information which is impossible to determine in any other way. "Many of our scientific colleagues who have waited patiently for the results of this mission will be astonished with what the final catalogue contains" said Professor Hog, originator of he Tycho Catalogue concept, and one of the hiving forces behind the mission.
In thousands of cases, the stars are seen to be variable by Hipparcos. In these cases, the light output from he star changes with time, and these changes have been accurately measured by the satellite. Astronomers rely on a subset of variabl
No affiliations
No associations
LandOfFree
Hipparcos to deliver its final results catalogue soon does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Hipparcos to deliver its final results catalogue soon, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hipparcos to deliver its final results catalogue soon will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1357534