FUNDAMENTAL FUNDAMENTAL

ASTRONOMYASTRONOMY

Magda StavinschiMagda StavinschiAstronomical Institute of the Romanian AcademyAstronomical Institute of the Romanian Academy

No indication No indication of the of the distancedistance

to the objectsto the objects

The astrometric information is generally NOT the direction from which the light arrives, but a quantity more directly related to the geometric position of the celestial body in space in a certain reference coordinated system.

To achieve this one we must apply a certain number of corrections to the apparent direction in which the celestial body seems to lie.

The ensemble of these corrections constitutes the reduction of observations.

We intend to summarize all the possible effects, since the parameters that characterize some of them are often unknowns in the reduction of observations.

GEOMETRICAL EFFECTS

Several geometrical phenomena affect the transformation between

the instrument and the sky.

One is a purely geometrical transformation; others are due to kinematic properties of the ensemble Earth-celestial body.

FIELD-TO-FOCUS TRANSFORMATION

The final objective of an astrometric observation is to determine the position in the sky, in some C.R.F.

But, in many cases, the field of view of the instrument is limited and one has to refer the observation to neighboring objects

which are part of the C.R.F., or link to it.

For this, it is convenient to use a local system of celestial coordinates centered at a certain point A (α0, δ0).

The equatorial coordinates of a point in the vicinity of A are

 α0 + Δα , δ0 + Δδ

The image of this region of the celestial sphere on an ideal focal surface is planar

 one has to transform the differential coordinates Δα and Δδ into linear coordinates.

It is done by a conic projection from the center

of the unit celestial sphere on A.

Ax, Ay are tangents to the declination small circle => increasing right ascensions,

along the celestial meridian, the positive direction =>N

This local system of coordinates = standard coordinates

The transformation differential coordinates => standard coordinates

gnomonic or central projection

Annual ParallaxAnnual Parallax

apparentapparent displacement of a star displacement of a star on the celestial sphere on the celestial sphere

due to the due to the orbital motionorbital motion of the Earth of the Earth.

Correcting for parallax => the direction of the starCorrecting for parallax => the direction of the staras seen from the as seen from the barycenter barycenter BB of the Solar System. of the Solar System.

In evaluating In evaluating stellar parallaxesstellar parallaxes, , we assume that the observation we assume that the observation is performed from the is performed from the center of the Earthcenter of the Earth..

This is no longer This is no longer the case for the case for

bodies in the Solar Systembodies in the Solar System..

Let us observing a planet Let us observing a planet PP;; the vector the vector OP OP observer-planetobserver-planet has to be considered as the sum of has to be considered as the sum of 33 vectors in a vectors in a barycentric R.Sbarycentric R.S.:

OE, EB, BPOE, EB, BP

OE: obs - Earth center at time t of observation. It rotates around the axis of the Earth; produces a diurnal apparent motion of the direction of the planet = diurnal or geocentric parallax (observation performed from an artificial satellite)

EB: Earth center – SS barycenter at the time t (given by ephemerides)

BP: SS barycenter - planet. at t' when the light which reached the observer at t was emitted by P. (It takes the parallax proper, but also the planetary aberration, effect produced by the finite speed of light.)

=> direction in which the planet is visible at t is given byOP = OE(t) + EB(t) + BP(t')

Proper motions (p.m.)(p.m.)

= projection on the sky of the motion of a star w.r.t. the SS barycenter

= combination of the actual motions of the star and of the Sun within the Galaxy

p.m. μ in terms of yearly variations of α and δ

α0,δ0 of the star are given for a date t0

=>=> the coordinates at time t are:

α = α0 + (t - t0) μα

δ = δ0 + (t - t0) μδ

OPTICAL EFFECTS

They are produced by various They are produced by various properties of lightproperties of light:: •              finite velocity, finite velocity, •              non-linear propagation in gravity fields, non-linear propagation in gravity fields, •              its ondulatory nature.its ondulatory nature.

ABERRATION

due to the relative motion of the source P and the observer

The apparent direction from which the light is coming at t = the direction of the point where the light source was at t - Δt

(Δt = the time during which the light traveled from P to the observer)

In Newtonian space, if In Newtonian space, if rr (|r| = (|r| = rr) is the ) is the true true position vector, position vector,

=>=> the the apparentapparent position is given by position is given by rr’’, such that , such that

r' = r + r' = r + rr V/ V/cc

(V = velocity of the observer w.r.t. the star; (V = velocity of the observer w.r.t. the star; cc = speed of light) = speed of light)

VV can be split in can be split in 33 components components::

V = VV = V00 + V + V

EE - V - VSS

VE = velocity of Earth center of mass w.r.t. SS barycenter

It gives rise to the annual aberration ,in which V is replaced by VE.

Planets: the total aberration, caused by VE – VS,

is the planetary aberration.

VS = star velocity w.r.t. the SS barycenter

(For starsstars: not known; it is neglected:the corresponding displacement is taken into account by the p.m. of the star.For planetsplanets: known from ephemerides)

V0 = velocity of the observer w.r.t. Earth center of mass.

On the ground it is obtained from the Earth rotation parameters => diurnal aberration.

On an artificial satellite, it is the orbital aberration derived from the motion of the satellite.

EssentiallyEssentially: both : both velocitiesvelocities and and directionsdirections be computed in a be computed in a common reference framecommon reference frame. .

All of these are not sufficient for All of these are not sufficient for accurate astrometryaccurate astrometry. .

For the second order, one must make the computations For the second order, one must make the computations within the framework of within the framework of general relativitygeneral relativity..

Relativistic Light DeflectionRelativistic Light Deflection

A massive body produces a curvature of the space, and light is deflected towards the mass(following the geodesics of the space).

The effect is maximummaximum in the immediate neighborhood of the Sun (to 1.7").

Of the order of 4 mas in the perpendicular direction.

REFERENCEREFERENCE

SYSTEMS & FRAMESSYSTEMS & FRAMES

In In astronomy astronomy is ais a

reference system (R.S.), which is a theoretical concept

reference frame (R.F.)reference frame (R.F.), , a a practicalpractical realization of a R.S., which provides a realization of a R.S., which provides a

means of means of assigning coordinatesassigning coordinates to an object. to an object.

oror

REFERENCE SYSTEM

system of coordinates axes built in such a way that one might qualitatively assign

numbers, which represent unequivocally the position and the motion of material points

-        celestial reference system for positions, motions and dynamics of celestial bodies;

-        terrestrial reference system for positions on the Earth and its environment.

In both cases, no physical axes or great circles that would materialize the coordinate system.

One has to use the existing material points (or celestial bodies) to which positions should be referred.

Necessarily: by what procedure these ones can be used for determining the coordinates of an observed object?

The ensemble of fiducial points and algorithms to be used in the procedure = reference frame

IDEAL REFERENCE IDEAL REFERENCE SYSTEMSYSTEM

Dynamical definition

The Newtonian definition, applicable only locally in general relativity:

W.r.t. an ideal dynamical C.R.S., celestial bodies move such as the equations of motion have no kinematicno kinematic acceleration (due to the rotation, as in Coriolis acceleration, or due to an nonuniform linear motion).

 Kinematic definition

An ideal kynematic C.R.F. assumes that there existsin the Universe a class of objects, which have no global systematic motion and therefore are not rotating in the mean.

One must admit that its physical meaning is questionable: non-rotating w.r.t. what?

Actually, this means that there are no large regions in the sky where p.m. of these objects present a systematic behavior.

REFERENCE SYSTEMS

One can proceed in both directions and identify a physical structure that has the property required. At this step, one speaks of reference systems proper.

Dynamical definition

General choice: SSSS as a whole, center of coordinate axes in the SS barycenter.

Sometimes, other systems, e.g. for the motion of the Earth-Moon system or of artificial satellites: geocentric dynamical system.

Quasars (& other distant extragalactic objects) are so distant that, in practice, they have a transverse motion of the order of the cosmological recession rate, a very improbable situation.

Kinematic definition

The choice of a lot of most stable such objects as fiducial points is adequate at the level of a few 0.01"

The system obtained = extragalactic celestial R.S.

CONVENTIONAL REFERENCE SYSTEM

Choice is made => => one has to associate a quantitative model of the structure selected

It is based upon numerical values of a number of parameters

(not known exactly, since they result from observations)

one has to assign them some values the model is only an approximation to the ideal R.S. it is called the conventional reference system.

Dynamical definitionDynamical definition

The conventional system adopted in the past was determined by a choice of values of fundamental parameters:-        masses of planets and satellites, -        initial conditions of their motions, some specific constants (precession and nutation, constant of aberration; etc.).

They are part of the system of astronomical constants periodically revised by the IAU (1976)

This approach to C.R.F. frames is now obsolete and thedynamical definition is abandoned in favor of a kinematical definition.

Kinematic definitionKinematic definition

Not much modeling is necessary for an extragalactic R.S. =official IAU conventional R.S., called

International Celestial Reference System (ICRS)

starting January 1, 1998

the principal planeprincipal plane of the new conventional C.R.S. as near as possible to the main equator at J 2000.0main equator at J 2000.0 and

 the originorigin in this principal plane

as near as possible to the dynamical equinox of J 2000.0dynamical equinox of J 2000.0.

INTERMEDIARY REFERENCE SYSTEMTogether with the adoption of the ICRS

(axes independent of the vernal equinox)a new definition of the intermediary R.S. was needed.

Starting 1st January 2003, the new system is defined by:

Pole =Pole = Celestial Intermediate Pole Celestial Intermediate Pole (CIP) (CIP) Its motion is specified in the Geocentric C.R.S.

by the motion of the Tisserand mean axis of the Earth (the mean surface geographical axis) with periods >> 2 days.

OriginOrigin = = Celestial Ephemeris OriginCelestial Ephemeris Origin (CEO) (CEO) defined on the equator of the CIP such that it is insensitive

to changes in models for precession and nutation at the arc level. The corresponding point on the ITRS is the

Terrestrial Ephemeris OriginTerrestrial Ephemeris Origin (TEO). (TEO).

CONVENTIONAL REFERENCE FRAMES

The final step is to materialize the C.R.S. by assigning coordinates to a certain number of fiducial points (stars or extragalactic objects) in this system.

Result: reference frame

or, better, conventional reference frame

presented in the form of a catalogue of positions and proper motions.

For a dynamical definition, one has to establish(using the conventional model)

a numerical theory of the motion of planets, and the position of reference stars are determined w.r.t.

the observed positions of planets. => R.F. is realized by a fundamental star catalogue.

The last such catalogue is the The last such catalogue is the FK5FK5

The kinematic extragalactic R.S. is realized by ICRF = a catalogue of positions of

212 quasars and other extragalactic radiosources built from a combination of observations by VLBI

ICRS origin = SS center of mass (barycenter) (the only point of the SS, whose motion in the Galaxy is

not perturbed by the presence of planets, satellites and the Sun).

International Terrestrial Reference FrameInternational Terrestrial Reference FrameITRFITRF

positions and motions (due to plate motions) of a certain number of points on the surface of the Earth

To obtain the celestial equatorial coordinates rather than the hour angle H at the International Meridian,

we note that α is related to H by

α = T + H

T = Greenwich sidereal time

ROTATION ROTATION OF THE EARTHOF THE EARTH

TIMETIME

ROTATION OF THE EARTHROTATION OF THE EARTH- complicated ensemble of physical phenomena

- resulting motion is a complex function of time

It could be divided in 2 groups:

- precession and nutation, which describe the motion of the Earth's rotation axis in the C.R.S.

- Earth's rotation proper together with the polar motion

The The Earth's rotation axisEarth's rotation axis is is not fixednot fixed in space. in space. Like a rotating toy top, the direction of the rotation axis executes a slow precessionslow precession with a period of 26,000 years26,000 years.

Pole Stars are TransientPole Stars are Transient

Due to the precession of the rotation axis:- Polaris will not always be the Pole Star or North Star. - in 13,000 years, Vega (Lyra) = North Celestial Pole.- in 26,000 more years, Polaris will once again be the Pole Star.

POLAR MOTIONPOLAR MOTION

EulerEuler (1758): (1758): rotation axis moves w.r.t. an Earth-fixed R.F. rotation axis moves w.r.t. an Earth-fixed R.F.

ChandlerChandler (1891): (1891):determination from observations of the geographical determination from observations of the geographical latitudes of astronomical observatories. latitudes of astronomical observatories.

Chandler periodChandler period ( (435 days435 days) different from the ) different from the Euler periodEuler period ( (304 days304 days) because of the non-rigidity and the ) because of the non-rigidity and the inhomogeneous mass distribution of the Earth. inhomogeneous mass distribution of the Earth.

The The radius of the Chandler wobbleradius of the Chandler wobble of the rotation pole of the rotation pole is about 6 m. is about 6 m.

Polar motionsPolar motions caused by: caused by:

-gravitational forces of Sun and Moongravitational forces of Sun and Moon

- geophysical processes within atmosphere, oceans and geophysical processes within atmosphere, oceans and interior of the Earth. interior of the Earth.

1962: IPMS1962: IPMS (International Polar Motion Service) (International Polar Motion Service) 1988: IERS1988: IERS (International Earth Rotation Service) (International Earth Rotation Service)

1899 - ILS 1899 - ILS (International Latitude Service)(International Latitude Service)

Precession of the EquinoxesPrecession of the Equinoxes

Rotation axis is precessing in space=> orientation of the Celestial Equator precesses too, with the same period

position of the equinoxes changing slowly w.r.t. background stars

Precession of the equinoxes => α and δ change very slowly over a 26,000 year26,000 year period.

This effect is negligibly small for casual observing, but is an important correction for precise observations.

Earth mean figureEarth mean figure:ellipsoid flattened at its poles

(equatorial radius is about 21 km > polar radius).

There is thus an equatorial bulgeequatorial bulge on which the luni-solar attractionluni-solar attraction induces a torquetorque which tends to rock the equatorequator towards the eclipticecliptic.

Because of its rotation, exactly as a top, the Earth is animated by a precessional motionprecessional motion:

the rotation axis is doing a large motion around the perpendicular to the ecliptic in about 25,600 years25,600 years.

Relative positions of MoonMoon, EarthEarth and SunSun vary with tt => periodic additional motionsperiodic additional motions (nutationsnutations);their periodsperiods directly related to the periods of the periods of the orbital motionsorbital motions of the planetsplanets around the SunSun and of the MoonMoon around the EarthEarth.

Main Main nutationnutation periods periods:13.66 days, ½ year, 1 year, 9.3 years, 18.6 years.13.66 days, ½ year, 1 year, 9.3 years, 18.6 years.

Nutational motions in space, represented as angle variationsangle variations in longitudelongitude & in obliquityobliquity.

They are elliptical.elliptical. They can also be represented as the sum of two circular nutationssum of two circular nutations with the same periodsame period but different amplitudesdifferent amplitudes & directions (directions (one prograde, one retrograde).

NUTATIONNUTATION

Babylonians & GreeksBabylonians & Greeks: Earth : Earth restsrests at the center of the universe! at the center of the universe! = = = = = = = = = = = = = = = = = = = = = = = =

!!! Earth itself rotated on its axis !!!!!! Earth itself rotated on its axis !!!

Heraclides, AristotleHeraclides, Aristotle (4rd century B.C.) (4rd century B.C.)

= = = = = = = = = = = == = = = = = = = = = = =?! ?! PtolemyPtolemy (2nd century A.D.) (2nd century A.D.) ?! ?!

''provedproved' that the Earth could not move ' that the Earth could not move = = = = = = = = = = = == = = = = = = = = = = =

CopernicusCopernicus (16th century) (16th century)convincing arguments for the motion convincing arguments for the motion

EARTH’S ROTATION VARIABILITYEARTH’S ROTATION VARIABILITY

Its variability relative to the body of the planet or in inertial space is caused by the:

- gravitational torque exerted by the Moon, Sun and planets, - displacements of matter in different parts of the planet and - other excitation mechanisms.

The observed oscillations can be interpreted in terms of:The observed oscillations can be interpreted in terms of:- mantle elasticity, - Earth flattening, - structure and properties of the core-mantle boundary, - rheology of the core, - underground water, - oceanic variability,- atmospheric variability on time scales of weather or climate

Period of rotation of the Earth (Period of rotation of the Earth (LODLOD) ) assumed assumed constantconstant

until the 20th century, until the 20th century,

apart from a apart from a secular changesecular change

KantKant (1754) predicted that friction (1754) predicted that friction with the tidal forces on Earth with the tidal forces on Earth

would cause a would cause a decelerationdeceleration of the Earth's rotation.of the Earth's rotation.

FerrelFerrel and and DelaunayDelaunay (19 (19thth century) confirmed this effect. century) confirmed this effect.

Secular decreaseSecular decrease of the rotation rate causes a LOD of the rotation rate causes a LODincrease of about increase of about 2 ms/century2 ms/century

1936 (N. Stoyko): 1936 (N. Stoyko): seasonalseasonal irregularities irregularities

Days in Days in MarchMarch about about 1 ms1 ms longer than days in longer than days in JulyJuly. .

Abrupt,Abrupt, irregularirregular changes of changes ofthousandths of a secondthousandths of a second (interactions between motions in the (interactions between motions in the Earth's outer layers and core?)Earth's outer layers and core?)

The measurements of the Earth's rotation are The measurements of the Earth's rotation are under the form of time series of the so-calledunder the form of time series of the so-called

Earth Orientation ParametersEarth Orientation Parameters (EOP) (EOP)

UNIVERSAL TIMEUNIVERSAL TIME

UT1UT1 = time of the Earth clock (one revolution in about 24h)24h). Practically proportional to the sidereal timesidereal time. Excess revolution time = length of daylength of day (LOD)

Greenwich Mean Sideral Time (GMST)Greenwich Mean Sideral Time (GMST) = angle computed = angle computed from the from the UT1UT1 referred to the instantaneous position of the referred to the instantaneous position of the axis of rotation of the Earth (axis of rotation of the Earth (instantaneous poleinstantaneous pole). ).

COORDINATES COORDINATES OF THE POLEOF THE POLE

xx , y: Celestial Ephemeris PoleCelestial Ephemeris Pole (CEP), relative to IRP (IRP (IERS Reference Pole).

CEPCEP differs from the instantaneous rotation axisinstantaneous rotation axis by quasi-diurnalquasi-diurnal terms with amplitudes under 0.01".

x-axis:x-axis: in the direction of IRMIRM (IERS Reference Meridian) y-axis:y-axis: in the direction 9090°° West West longitude.

Timing techniques

A class of astrometric techniquesastrometric techniques is not based upon analyses of electromagnetic waves received from space, but on measurement of time intervals between events one of which, at least, originates from space or is connected with it.

Accuracies of the order of 10-14 or 10-15 .

10-16 is expected in the near future.

International Atomic Time (TAI): time reference established by the BIH (now BIPM) on the basis of atomic clocks operating in various establishments in accordance with the definition of the second, the unit of time of SI

TAI is a coordinate time scale defined in a geocentric R.F. whose scale unit is the SI second, realized on the rotating geoid

LEGAL SCALE TIMESLEGAL SCALE TIMES

based on UTC, differing from TAI by an integer numberinteger number of seconds of seconds.

LEAP SECONDSLEAP SECONDS

decided by IERS:decided by IERS:|UTC – UT1| < 0.9 s |UTC – UT1| < 0.9 s Now: Now: UTC - TAI = - 32 sUTC - TAI = - 32 s

LASTLAST: 1 January 19991 January 1999

NEXT:

2005 Dec 31 23h 59m 59s2005 Dec 31 23h 59m 59s2005 Dec 31 23h 59m 60s2005 Dec 31 23h 59m 60s2006 Jan 1 0h 0m 0s2006 Jan 1 0h 0m 0s

For astronomy: For astronomy: terrestrial time TTterrestrial time TT, , ideal form of ideal form of TAITAI, ,

it extends without discontinuity the old it extends without discontinuity the old Ephemeris TimeEphemeris Time (TE) in a (TE) in a geocentric R.F.geocentric R.F.

TT = TAI + 32.184 sTT = TAI + 32.184 s

The theoretical basis for The theoretical basis for TETE is wholly is wholly non-relativisticnon-relativistic. . 1984: : ETET replaced by the two relativistic timescales replaced by the two relativistic timescales

Barycentric Dynamical Time (TDB) (TDB)

Terrestrial Dynamical Time (TDT). (TDT). In In practicepractice, ,

the length of the the length of the TE secondTE second = = = the length of the = the length of the TDBTDB or or TDT secondTDT second.

SPACE ASTROMETRYSPACE ASTROMETRY

AdvantagesAdvantages

Absence of atmospheric refraction and turbulence ( image is a fixed diffraction pattern, which is much more accurate than on the Earth).

Quasi-absence of mechanical torques modifying the position of the image of the center of the field when the instrument changes orientation.

Possibility to observe the entire sky with a single instrument.

HIPPARCOS HIPPARCOS missionmission

The principle of HIPPARCOS was invented by Lacroute in 1966 .More than 10 years elapsed before space technology allowed serious consideration of its development.

Later E. Hog added the concept of scientific use of the star-mapper with 2 color channels and the Tycho experiment.

HIgh Precision PARallax COllecting Satellite

Hipparchus of Rodhesof Rodhes190-120 BC190-120 BC

-calculated the length of the year to within 6.5 min;

-discovered the precession of the equinoxes

-first known star catalogue (1080 stars)

Launched: August 8, 1989

Very elongated orbit instead of the expected geostationary one. Perigee 500 km high and an apogee close to 36500 km. Period = 10h 40min.

Last observation: March 1993.

General principle of HIPPARCOS

- global astrometry instrument - conceived to measure, or in due cause to determine,

large angles on the sky

HIPPARCOS Final Catalogue

Two catalogues were produced independently.

The most detailed and updated reduction is presented in Vol. 1 & 3 of the published catalogue (ESA, 1997).

The resulting astrometric parameters obtained by each consortium were not identical.

For obtaining a unique consistent catalogue, a merging of the two was performed.

Contents of the Hipparcos Catalogue

Published by Published by ESAESA (1997): (1997):

16 printed volumes and a set of ASCII CD-Rom discs16 printed volumes and a set of ASCII CD-Rom discs

117,955117,955 entries forentries for astrometry astrometry &&

118,204118,204 for thefor the photometric photometric resultsresults

Astrometric results

Positions and p.m. given in ICRS for mean epoch of observations 1991.25.

  Median standard uncertainty for:

 star positions with Hp < 9 at epoch is

0.77 mas (in α cos δ) and 0.64 mas (in δ) yearly p.m.: 0.88 mas/yr (in α cos δ) and 0.74 mas/yr (in δ)  parallaxes: 0.97 mas

Photometric results

median photometric uncertainty for Hp < 9 is 0.0015 mag.

11,600 recognized or suspected variables.

TYCHO CATALOGUETYCHO CATALOGUE

1,058,332 entries, < VT ~10.5 mag

(limiting magnitude VT ~11.5 mag)

Median astrometric standard uncertainty (VT < 9 mag) 7 mas

for position at 1991.25

Photometric median standard uncertainty: 0.012 mag for VT

For the entire catalogue: 25 mas for position

0.06 mag for VT photometry

Tycho-2 CatalogueTycho-2 Catalogue

positions and magnitudes of 2,538,913 stars, based on satellite data,

only for an observation epoch close to 1992.5

Median uncertainty - the same as for the Tycho for bright starsbright stars (VT < 9): 7 mas,

for all stars:all stars: 60 mas.

Mean standard uncertainty in p.m. is 2.5 mas/yr

SPACE GLOBAL ASTROMETRY PROJECTSSPACE GLOBAL ASTROMETRY PROJECTS

Ground-based astrometry precision will always remain limited by the atmosphere.

0.01 mas (or better) required by the many astrophysical problems cannot generally be met from the Earth =>=> only space astrometry can satisfy it.

The main principles of Hipparcos, namely the double field of view, slow rotation of the satellite, and a specific sky scanning law proved to be inescapable basics that are present in all projects.

G A I AG A I A

GGlobal lobal AAstrometry strometry IInstrument for nstrument for AAstrophysicsstrophysics

Based upon HIPPARCOS main principles Based upon HIPPARCOS main principles with two fields of view separated by 106°. with two fields of view separated by 106°.

It is intended to be placed on a It is intended to be placed on a Lissajous-type eclipse-free orbit Lissajous-type eclipse-free orbit around the Lagrange point Laround the Lagrange point L

22

of the Earth-Sun system. of the Earth-Sun system.

LAUNCH: LAUNCH: Dec-2011Dec-2011   END:   END:20202020

OBJECTIVES: OBJECTIVES:

The The largestlargest and most and most preciseprecise three-dimensional chart three-dimensional chart of our Galaxy by providing unprecedented of our Galaxy by providing unprecedented

positional positional and and radial velocityradial velocity measurements measurements

for about for about one billion starsone billion stars in our Galaxy and throughout the Local Group. in our Galaxy and throughout the Local Group.

This will amount to about 1% of the Galactic stellar population.

Combined with astrophysical information for each star, provided by on-board multi-color photometry, will have the precision necessary to quantify the early formation, and subsequent

dynamical, chemical and star formation evolution of the Milky Way Galaxy.

Additional Additional scientific productsscientific products:

• detection and orbital classification of tens of thousands of extra-solar planetary systems;• a comprehensive survey of objects ranging from huge numbers of minor bodies in our SS, through galaxies in the nearby Universe, to some 500000 distant quasars; • stringent new tests of general relativity and cosmology.

SIM SIM PlanetQuestPlanetQuest

Scheduled for launch in Scheduled for launch in 20112011: : positions and distances of stars positions and distances of stars several hundred timesseveral hundred times more accurately more accurately than any previous program. than any previous program.

This accuracy will allow it to determine This accuracy will allow it to determine the the distances to starsdistances to stars throughout the galaxy throughout the galaxy and to probe nearby stars forand to probe nearby stars for Earth-sized planets. Earth-sized planets.

IAU WORKING - GROUPIAU WORKING - GROUP  

THE FUTURE DEVELOPMENT OF GROUND-BASED ASTROMETRY

FDGBAFDGBA

As the Newsletter No.1 of the IAU 2000, Commission 8 announcedAs the Newsletter No.1 of the IAU 2000, Commission 8 announced

The post-Hipparcos era has brought an element of uncertainty as to the goals and future programs for all of ground-based astrometry

The WG has to identify scientifically important programs that can be realized using GBA or related observations, and to study what kind of modifications, upgrades or additions to the existing instruments should be performed in order to provide useful astronomical information with necessary accuracy, keeping in mind what the future astrometric satellites will contribute

http://www.astro.ro/wg

POSSIBLE PROGRAMSPOSSIBLE PROGRAMSfor FDGBAfor FDGBA

-astrometric observations of some natural satellites, asteroids & comets with small or medium-sized telescopes - monitoring selected asteroids approaching the Earth - observations of artificial objects and space events and other natural phenomena generating hazards in the vicinity of the Earth - improving double star orbits - astrometric re-reduction of old observations of bright main belt asteroids obtained at Golosiiv in the system of modern catalogues such as Tycho-2 to improve asteroid orbits - astrometric observations of the areas around extragalactic radiosources to extend Hipparcos system to the faint stars - rediscovering of recently discovered asteroids with the help of digital plate archive that we are creating now as a part of the work on the integration of our plate archive into national and international virtual observatories.

SELECTED BIBLIOGRAPHYSELECTED BIBLIOGRAPHY

Kovalevsky, J.,Modern Astrometry, Springer-Verlag, 1994, 2002

Danjon, A.,Astronomie Générale, 1980, Librairie Blanchard, Paris

Soffel, M.H., Relativity in Astrometry, Celestial Mechanics and Geodesy,Springer -Verlag, Berlin, Heidelberg, 1989

Woolard, E.W. and Clemence, G.M. Spherical Astronomy, Academic Press, New York, 1966

http://www.iers.org/http://scienceworld.wolfram.com/astronomy/Time.htmlhttp://cdsweb.u-strasbg.fr/hipparcos.htmlhttp://sci.esa.int/science-e/www/area/index.cfm?fareaid=26http://aira.astro.ro/wg/