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Author(s) of the publication: A. Finkelstein

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One important division of astronomy-fundamental coordinate and time service (FCTS) - has appeared at the junction of astrometry, ephemeris astronomy, celestial mechanics, geodynamics and thanks to new ground-based and space measuring technologies, bandwidth recording and high-rate data communications. Today all this is in the mainstream of IAA work.

Pages. 23


By Andrei FINKELSTEIN, Dr. Sc. (Phys. & Math.), Director of the Institute of Applied Astronomy (IAA), Russian Academy of Sciences

Revolutionary changes have occurred in the science of astronomy over the last ten to fifteen years. These changes relate above all to problem solving in a wide range of areas-from traditional astrometry and ephemeris astronomy to geophysics, global tectonics, physics of the ocean and of the atmosphere, astrophysics and cosmology. Verification of basic physical theories is likewise an important part of this work. Ever higher demands are now being made on the accuracy of coordinate-time measurements, the upper boundary of which is in the millimeter (relative to terrestrial coordinates) and in the submillisecond (relative to the coordinates of galactic and extragalactic objects, and of celestial bodies within the solar system) regions of the arc. Researchers are now armed with novel measuring technologies (space technologies too), such as radiolocation of small and large planets, laser detection and ranging, the global navigation systems GPS, GLONASS and DORIS; or very long baseline interferometers (VLBI), astrometric satellites, ground- and space-based interferometers. All that has made it possible to up observation accuracy by 3 to 5 orders.

Simultaneously, innovative information and telecommunication technologies are being assimilated so as to bring together dozens and hundreds of instruments on different continents into integrated global networks in real time; such technologies can process as broadcast dataflows from each station at a rate of dozens of gigabits per second. And last, we are almost through with the work on long term (up to ten years) international observation programs, CORE programs in particular, that cover dozens of countries within permanently operating networks. Let me stress that our research center, IAA, is actively involved in these breakthrough efforts.

Yet ephemeris astronomy is still the main line of our research. Now, ephemeris astronomy takes in high-precision precomputation and evaluation with respect to all types of observations of various objects in the universe. We are determining the basic astronomical constants, verifying the general theory of relativity, attacking the problems of navigation, of space flights planning and so forth.

Our researchers have developed a program for studying new phenomena in ephemeris astronomy, one that has no analogs in the world in its universality. Once in command of it, any expert can formulate as good as any problem explicitly, in ordinary astronomical terms. Our program makes it possible to compute the ephemerides of the sun, of large and small planets, comets as well as of any points on their surface. It will enable us to compute the ephemerides of space probes and of artificial satellites of the earth. This program boosts the modeling precision greatly compared with conventional techniques. It enables not only classical observation methods but also those involving radar, radiolocation and radiointerferometry with the aid of GPS, GLONASS and DORIS, and by means of laser detection and ranging of artificial earth satellites and the moon.

Our research institute has created a system of planetary ephemerides, EPM-2002, which, along with the analogous DE-405 of NASA's Jet Propulsion Laboratory, is a well-spring of knowledge on the large planets and the moon. In the course of this work we made use of the data obtained in 300,000 radiotechnical observations of interior planets, Mars and Jupiter, and of the results of optical observations of outer planets.* This way we got an idea of the correlation dynamics of accuracies shown by the world's best ephemerides EPM and DE in 1991, 1996, 1999 and 2002. In some parameters, our results are even better than those of the DE-405 system developed abroad. Small wonder that our computations were used in testing the NASA-designed ephemeris support of the Martian satellite, MARS Global Survey (MGS).

Geodynamics and astrometry are another important area of our research. Beginning in the 1990s, we got down to regular work in loca-


* Internal and outer problems are determined by their position relative to the earth.- Ed.

Pages. 24


ting and computing the coordinates of radio sources and parameters of earth orientation (PEO) on the basis of data obtained with the aid of most up-to-date technical facilities. The accuracy of such methods is among the world's highest. Let me add: our Institute is the world's only research center involved with the proximate analysis of observation results by using the basic methods for determining parameters of earth orientation.

Besides, we are going ahead with the work of ascertaining the coordinates and rates of 152 stations and 337 radio sources employed for studying variations of long bases, deformations of the earth crust, and for constructing catalogs of these radio sources within the international system ICRS. This is a much more complicated task than that of determining earth orientation parameters, for it involves locating the coordinates well correlated with other numerical values, above all with the parameters of the atmosphere and time. To get on top of this problem we have developed the multipurpose QUASAR package designed for a multiserial processing of VLBI observation data in global networks*.

Our idea boils down to this: use different methods in assessing both regular parameters (constant coefficients of resolutions within a 24 h interval) and those of stochastic (probabilistic) nature. This is the most effective way of assessing random elements of the polar coordinates, universal time, the humid component of the tropospheric delay and atomic time scales.

Such systems as VLBI, GPS and SLR are now the commonest ground-based facilities of basic coordinate-time support (BCTS). Each has a good future. For instance, in the last thirty years VLBI has been improving its accuracy by


See: A. Finkelstein, "Radiointerferometric Network QUASAR", Science in Russia, No. 5, 2001.-Ed.

Pages. 25


Structure of the system of ephemeris astronomy.

Accuracy of PEO parameters of earth orientation determination by VLBI, SLR and GPS data.

Center

X, mas

Y, mas

UT, 0.1 ms

ULBI data

GSFC, USA

0.11

0.07

0.06

RASIAA

0.14

0.12

0.05

USNO, USA

0.14

0.12

0.06

SLR data

TSUP (Right Control Center), Russia

0.18

0.19

-

RASIAA

0.22

0.2

-

OUT, Netherlands

0.35

0.35

-

CSR, USA

0.41

0.40

-

GPS data

 

X, mas

Y, mas

LOD.O.I ms

CODE, Switzerland

0.04

0.15

0.24

JPL, USA

0.06

0. 1 1

0.34

GFZ, Germany

0.08

0.10

0.33

FMR, Canada

0.09

0.18

0.37

SIO, USA

0.10

0.14

0.22

RASIAA

0.17

0.13

0.32

ESOC, Europe

0.12

0.14

0.34

NOAA, USA

0.17

0.37

0.60

two orders in just 15 years. This has become possible through expanding the registration bandwidth and increasing the number of radio telescopes. The GPS facilities have come to be upgraded thanks to the use of a new generation of multifrequency receivers and due to hundreds of GPS stations set up on all continents. But the situation is different in what concerns laser detection and ranging technologies on orbital satellites. There has been no improvement ever since the late 1980s in de- termining earth rotation parameters and global bases. These facilities must have exhausted their potential. Since we in Russia have been unable to design laser rangers in the sub-centimeter band, the focus will still be on VLBI interferometry and GPS/GLONASS.

What all this means-given innovative ground- and space-based measuring devices and their application techniques-is that relativistic astrometry concerned with phenomena in the domain of the general theory of relativity is now a hands-on problem. In conjunction with ephemeris astronomy and geodynamics, relativistic astrometry should help solve a hard puzzle. The point is that such

Pages. 26


Corrections for right ascensions  and declinations  of radio sources through QUASAR package.

Pages. 27


Radio sources mapped by the SVETLOYE - ZELENCHUKSKAYA radiointerferometer.

Radio source mapped by the SVETLOYE - ZELENCHUKSKAYA - KALYAZIN radiointerferometer.

Pages. 28


conventional notions as equator, ecliptic, polar motion and the like are based on Newtonian mechanics predicating absolute space and time. We can overcome this contradiction only by taking account of four-dimensional space-time dependences between the relativistic systems of readings as well as corresponding linkages between mathematical values and physical parameters. This approach has been developed in resolutions of the International Astronomical Union filed by research bodies of the United States, Germany and Japan in collaboration with our Institute, IAA. These documents define methods of transforming spatial and temporal coordinates. Accordingly, the two chief astronomical systems-ICRIS and ITRS- should be regarded as relativistic four-dimensional with the TCB (barycen-tric) and the TCG (geocentric) time. And so the barycentric reference system (BCRS) has been introduced for celestial coordinates, one that is intermediate between ICRS and ITRS.

In a decade or so, FCTS space facilities will come to play a major role: their accuracy of measuring the optical positions of stars is 10 to 20-fold higher than that achieved in the Hipparcos project (USA). In another development, NASA is to launch its FAME satellite to locate the positions of something like 40 mln stars in the 5 m - 15 m range, accuracy up to 50  of the arc. NASA will also launch its GAIA and ROMER projects (accuracy up to 10 - 2  of the arc) for stars and extragalactic objects in a range to 20 m . As to Russia, it zeroes in on the space radio- interferometer RADIOASTRON showing an accuracy of 100  of the arc in spotting radio sources. In addition, our Institute has designed relativistic models for positional observations to microsecond accuracy which, besides the post-Newtonian effects caused by the rotation and form of heavenly bodies, will also make for post-post-Newtonian solar effects.

Closely allied with this work is also our procedure of permanent registration of the structure of radio sources in RSLB data processing, with an angular resolution of 1 ms of the arc and higher. This mandatory reduction should be part of any contemporary software packages for analysis of high-precision astrometric, geodynamic and geodetic VLB I measurements. Furthermore, radio sources imaging is of considerable interest for a wide range of astrophysical problem solving.

Our scientists have also designed new nonlinear information methods for radio sources mapping. In particular, their accuracy has been demonstrated in mapping radio sources with submillisecond angular resolution. This work involved RSLB observation data obtained with the use of Svetloye-Zelenchukskaya and Svetloye - Zelenchukskaya - Kalyazin radio-interferometers. It takes but 20 or 30 minutes to make a map like that from geodetic VLB I observation data.

Our story will not be complete unless we say something about the many-sided and substantive activity of IPA in the publishing business. For instance, our Astronomichesky sbornik (Astronomical Collection} has been out in St. Petersburg for as long as 82 years already. In it you can find the geocentric ephemerides of the sun, moon and large planets; you will find data essential to physical observations of our luminary, data on solar eclipses as well as other bits of information on so many space objects. And without our Morskoi astronomichesky yezhegodnik (Maritime Astronomical Annual), now in the press for 74 years, no Russian naval ship will put out to sea or call at a port. The format of this yearbook has been changed a good deal of late: its right-hand pages now carry information on visibility spots for 67 lodestars within a span of three days. Also, we have modified tables of altitudes and azimuths, something that has made this annual a welcome aid to navigators (alongside our latest handbook, the Morskoi astronomichesky almanakh [Maritime Astronomical Almanac]. We do not depend any longer on data carried by other handbooks for navigators.

Our research staff has done a good job in drawing up catalogs of asteroids.* The interest in the small planets goes beyond their dynamic impact on the motion of other bodies in the solar system. One important reason for such preoccupation is the danger of their collision with our planet. Approaching the earth, asteroids, comets and other bodies pose a threat of global disasters involving climate changes, millions of victims and such kind of things. Some countries (USA, Japan, Britain) have worked out national programs for studying the asteroid hazard; as a matter of fact, all small celestial bodies above 1 km in diameter** should be spotted and identified.

We do not stand idly by either. Our catalog of 400 asteroids and 30 comets that may threaten the globe ascertains their orbits and supplies data on their dimensions, physical characteristics and on the potential energy of their impact should they collide with the earth. We also assess the consequences of a like disaster.

To sum up: research in fundamental coordinate and time service (FCTS) is a very difficult and multifarious job. However, the measuring systems now in use are quite effective based as they are on the latest know-how. Even though this work calls for great efforts and expenses, it will recoup with a vengeance: in fact, we cannot visualize the future of science at home and abroad without a knowledge of astronomy.


See: A. Litvak et al., "Cosmic Wanderers", Science in Russia, No. 2, 2002.-Ed.

** See: Ya. Renkas, "Eternal Monument", Science in Russia, No. 2, 2003.- Ed.

Illustrations supplied by the author.


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A. Finkelstein, ASTRONOMY: COORDINATE-TIME SUPPORT // London: Libmonster (LIBMONSTER.COM). Updated: 07.09.2018. URL: https://libmonster.com/m/articles/view/ASTRONOMY-COORDINATE-TIME-SUPPORT (date of access: 22.04.2021).

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