274:
216:(μas) and a reference axis stability of approximately 20 μas; this was an order-of-magnitude improvement over the previous reference frame derived from (FK5). The ICRF1 contains 212 defining sources and also contains positions of 396 additional non-defining sources for reference. The positions of these sources have been adjusted in later extensions to the catalogue. ICRF1 agrees with the orientation of the Fifth Fundamental Catalog (FK5) "
1501:
187:. In August 2021 the International Astronomical Union decided in Resolution B3 of its XXXIst General Assembly "that as from 1 January 2022, the fundamental realization of the International Celestial Reference System (ICRS) shall comprise the Third Realization of the International Celestial Reference Frame (ICRF3) for the radio domain and the Gaia-CRF3 for the optical domain."
1525:
1477:
1513:
1489:
947:
Fey, A. L.; Gordon, D.; Jacobs, C. S.; Ma, C.; Gaume, R. A.; Arias, E. F.; Bianco, G.; Boboltz, D. A.; Böckmann, S.; Bolotin, S.; Charlot, P.; Collioud, A.; Engelhardt, G.; Gipson, J.; Gontier, A.-M.; Heinkelmann, R.; Kurdubov, S.; Lambert, S.; Lytvyn, S.; MacMillan, D. S.; Malkin, Z.; Nothnagel, A.;
144:
It is useful to distinguish reference systems and reference frames. A reference frame has been defined as "a catalogue of the adopted coordinates of a set of reference objects that serves to define, or realize, a particular coordinate frame". A reference system is a broader concept, encompassing "the
252:
effects. The observations resulted in about 6.5 million group-delay measurements among pairs of telescopes. The group delays were processed with software that takes into account atmospheric and geophysical processes. The positions of the reference sources were treated as unknowns to be solved for by
713:
A reference system ... defines the origin and fundamental planes (or axes) of the coordinate system. It also specifies all of the constants, models, and algorithms used to transform between observable quantities and reference data that conform to the system. A reference frame consists of a set of
240:. ICRF2 is defined by the position of 295 compact radio sources (97 of which also define ICRF1). Alignment of ICRF2 with ICRF1-Ext2, the second extension of ICRF1, was made with 138 sources common to both reference frames. Including non-defining sources, it comprises 3414 sources measured using
351:
catalogue were aligned with the extragalactic radio frame. In August 1997, the
International Astronomical Union recognized in Resolution B2 of its XXIIIrd General Assembly "That the Hipparcos Catalogue was finalized in 1996 and that its coordinate frame is aligned to that of the frame of the
244:. The ICRF2 has a noise floor of approximately 40 μas and an axis stability of approximately 10 μas. Maintenance of the ICRF2 will be accomplished by a set of 295 sources that have especially good positional stability and unambiguous spatial structure.
819:
247:
The data used to derive the reference frame come from approximately 30 years of VLBI observations, from 1979 to 2009. Radio observations in both the S-band (2.3 GHz) and X-band (8.4 GHz) were recorded simultaneously to allow correction for
285:
of the solar system, a new feature over and above ICRF2. ICRF3 also includes measurements at three frequency bands, providing three independent, and slightly different, realizations of the ICRS: dual frequency measurements at 8.4 GHz
318:
band) for 678 sources. Of these, 303 sources, uniformly distributed on the sky, are identified as "defining sources" which fix the axes of the frame. ICRF3 also increases the number of defining sources in the southern sky.
45:, with axes that are intended to "show no global rotation with respect to a set of distant extragalactic objects". This fixed reference system differs from previous reference systems, which had been based on
435:-CRF3 had "largely superseded the Hipparcos Catalogue" and was "de facto the optical realization of the Celestial Reference Frame within the astronomical community." Consequently, the IAU decided that
352:
extragalactic sources with one sigma uncertainties of ±0.6 milliarcseconds (mas)" and resolved "that the
Hipparcos Catalogue shall be the primary realization of the ICRS at optical wavelengths."
383:, appeared in 2018 and has been described as "the first full-fledged optical realisation of the ICRS, that is to say, an optical reference frame built only on extragalactic sources." The axes of
233:
458:
1417:
161:, distributed around the entire sky. Because they are so distant, they are apparently stationary to our current technology, yet their positions can be measured very accurately by
237:
463:
339:
recommended "that observing programmes be undertaken or continued in order to ... determine the relationship between catalogues of extragalactic source positions and ... the
281:
ICRF3 is the third major revision of the ICRF, and was adopted by the IAU in August 2018 and became effective 1 January 2019. The modeling incorporates the effect of the
714:
identifiable fiducial points on the sky (specific astronomical objects), along with their coordinates, that serves as the practical realization of a reference system.
1384:(Technical report). Frankfurt am Main: International Earth Rotation and Reference Systems Service (IERS) and Verlag des Bundesamts für Kartographie und Geodäsie.
176:
resolved in
Resolution B2 of its XXIIIrd General Assembly "that the Hipparcos Catalogue shall be the primary realization of the ICRS at optical wavelengths." The
68:) is a realization of the International Celestial Reference System using reference celestial sources observed at radio wavelengths. In the context of the ICRS, a
770:
Ma, C.; Arias, E. F.; Eubanks, T. M.; et al. (July 1998), "The
International Celestial Reference Frame as Realized by Very Long Baseline Interferometry",
826:
258:
1545:
852:
79:
i.e., the reference frame is the set of numerical coordinates of the reference sources, derived using the procedures spelled out by the ICRS.
673:
Wilkins, G.A. (1990). Lieske, J. H.; Abalakin, V. K (eds.). "The Past, Present and Future of
Reference Systems for Astronomy and Geodesy".
1414:
820:"IERS Technical Note No. 35: The Second Realization of the International Celestial Reference Frame by Very Long Baseline Interferometry"
86:
53:, right ascension and declination" and had adopted as "privileged axes ... the mean equator and the dynamical equinox" at a particular
1389:
1372:
562:
241:
162:
98:
336:
229:
201:
173:
34:
948:
Ojha, R.; Skurikhina, E.; Sokolova, J.; Souchay, J.; Sovers, O. J.; Tesmer, V.; Titov, O.; Wang, G.; Zharov, V. (24 July 2015).
439:-CRF3 shall be "the fundamental realization of the International Celestial Reference System (ICRS) ... for the optical domain."
1409:
46:
1442:
1429:
204:
as of 1 January 1998. ICRF1 was oriented to the axes of the ICRS, which reflected the prior astronomical reference frame
1555:
262:
105:-CRF is an inertial barycentric reference frame defined by optically measured positions of extragalactic sources by the
50:
83:
911:"The Second Realization of the International Celestial Reference Frame (ICRF2) by Very Long Baseline Interferometry"
1467:
30:
205:
154:
166:
1379:
145:
totality of procedures, models and constants that are required for the use of one or more reference frames".
950:"The Second Realization of the International Celestial Reference Frame by Very Long Baseline Interferometry"
90:
1015:"The third realization of the International Celestial Reference Frame by very long baseline interferometry"
1014:
273:
282:
1296:
1244:
1188:
1036:
961:
922:
860:
779:
641:
590:
415:–CRF3) is based on 33 months of observations of 1,614,173 extragalactic sources. As with the earlier
1550:
1529:
1277:
Gaia
Collaboration (2022), "Gaia Early Data Release 3: The celestial reference frame (Gaia-CRF3)",
344:
181:
133:
228:
An updated reference frame ICRF2 was created in 2009. The update was a joint collaboration of the
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1234:
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1178:
1054:
1026:
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910:
797:
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113:
69:
949:
387:-CRF2 were aligned to a prototype version of the forthcoming ICRF3 using 2820 objects common to
120:
bodies, these reference frames are important because they do not exhibit any measurable angular
376:–CRF2), based on 22 months of observations of over half a million extragalactic sources by the
1385:
1368:
987:
558:
377:
106:
54:
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555:
Astrometry of
Fundamental Catalogues: The Evolution from Optical to Radio Reference Frames
965:
926:
783:
257:
across group-delay measurements. The solution was constrained to be consistent with the
1079:
578:
213:
1105:
579:"The Extragalactic Reference System of the International Earth Rotation Service, ICRS"
1539:
1318:
1058:
973:
801:
301:
1264:
1208:
431:
frequency bands. In August 2021 the
International Astronomical Union noted that the
180:
Celestial
Reference Frame (HCRF) is based on a subset of about 100,000 stars in the
1493:
999:
825:. International Earth Rotation and Reference Systems Service (IERS). Archived from
42:
1309:
1256:
1200:
1161:
Gaia
Collaboration; Mignard, F.; Klioner, S.; Lindegren, L.; et al. (2018), "
1049:
909:
Boboltz, David A.; Gaume, R. A.; Fey, A. L.; Ma, C.; Gordon, D. (1 January 2010).
1131:
1439:
1426:
1132:"The Hipparcos Catalogue as a realisation of the extragalactic reference system"
249:
209:
117:
1331:
488:"Resolution No. A4; Recommendations from the Working Group on Reference System"
748:
686:
448:
38:
1381:
IERS Technical Notes - The International Celestial Reference System and Frame
1221:
Lindegren, L.; Hernandez, J.; Bombrun, A.; Klioner, S.; et al. (2018), "
991:
700:
523:
The XXlIIrd General Assembly of the International Astronomical Union (1997).
347:." Using a variety of linking techniques, the coordinate axes defined by the
640:
The XXXIst General Assembly of the International Astronomical Union (2021).
453:
49:
that had published the positions of stars based on direct "observations of
486:
The XXIst General Assembly of the International Astronomical Union (1991).
132:-CRF are now the standard reference frames used to define the positions of
121:
1405:
883:
726:
607:
982:
308:
217:
1130:
Kovalevsky, J.; Lindegren, L.; Perryman, M.A.C.; et al. (1997).
294:
287:
158:
94:
89:
reference frame whose axes are defined by the measured positions of
1488:
1291:
1239:
1183:
1031:
792:
525:"Resolution No B2; On the international celestial reference system"
1460:
272:
1359:
Kovalevsky, Jean; Mueller, Ivan Istvan; Kołaczek, Barbara (1989)
427:-CRF3 were aligned to 3142 optical counterparts of ICRF-3 in the
1455:
300:) for 4536 sources; measurements of 824 sources at 24 GHz (
124:
since the extragalactic sources used to define the ICRF and the
577:
Arias, E.F.; Charlot, P.; Feissel, M.; Lestrade, J.-F. (1995),
340:
751:. U S Naval Observatory, Astronomical Applications Department
112:
and whose axes are rotated to conform to the ICRF. Although
1013:
Charlot, P.; Jacobs, C.S.; Gordon, D.; et al. (2020).
277:
Sky distribution of the 303 "defining sources" in the ICRF3
1110:
International Earth Rotation and Reference Systems Service
234:
International Earth Rotation and Reference Systems Service
1440:
ICRF page from the International Earth Rotation Service
220:" frame to within the (lower) precision of the latter.
642:"Resolution B3, On the Gaia Celestial Reference Frame"
459:
Barycentric and geocentric celestial reference systems
116:
implies that there are no true inertial frames around
1465:
1106:"The International Celestial Reference System (ICRS)"
238:
International VLBI Service for Geodesy and Astrometry
16:
Current standard celestial reference system and frame
1378:
Jean Souchay; Martine Feissel-Vernier, eds. (2006).
915:
American Astronomical Society Meeting Abstracts #215
464:
International Terrestrial Reference System and Frame
853:"NASA - New Celestial Map Gives Directions for GPS"
729:. U.S. Naval Observatory, Astronomical Applications
703:. U.S. Naval Observatory, Astronomical Applications
307:), and dual frequency measurements at 32 GHz (
749:"International Celestial Reference System (ICRS)"
727:"International Celestial Reference System (ICRS)"
701:"International Celestial Reference System (ICRS)"
608:"International Celestial Reference System (ICRS)"
75:(RF) is the physical realization of a reference
1406:International Celestial Reference System (ICRS)
1165:Data Release 2. The celestial reference frame (
200:The ICRF, now called ICRF1, was adopted by the
884:"The International Celestial Reference Frame"
814:
812:
810:
649:Resolutions adopted at the General Assemblies
532:Resolutions adopted at the General Assemblies
495:Resolutions adopted at the General Assemblies
165:(VLBI). The positions of most are known to 1
8:
1361:Reference Frames in Astronomy and Geophysics
1225:Data Release 2 – The astrometric solution",
675:Symposium - International Astronomical Union
668:
666:
1436:(defines ICRS and other related standards)
553:Walter, Hans G.; Sovers, Oscar J. (2000),
1308:
1290:
1238:
1182:
1048:
1030:
981:
791:
259:International Terrestrial Reference Frame
1367:, Volume 154 Kluwer Academic Publishers
23:International Celestial Reference System
1472:
1332:"Gaia Early Data Release 3 (Gaia EDR3)"
635:
633:
631:
629:
518:
516:
514:
512:
481:
479:
475:
128:-CRF are so far away. The ICRF and the
62:International Celestial Reference Frame
1365:Astrophysics and Space Science Library
202:International Astronomical Union (IAU)
681:. Cambridge University Press: 39–46.
7:
206:The Fifth Fundamental Catalog (FK5)
651:. International Astronomical Union
534:. International Astronomical Union
497:. International Astronomical Union
391:-CRF2 and to the ICRF3 prototype.
82:More specifically, the ICRF is an
14:
242:very-long-baseline interferometry
163:Very Long Baseline Interferometry
153:The ICRF is based on hundreds of
99:very-long-baseline interferometry
1523:
1511:
1499:
1487:
1475:
337:International Astronomical Union
331:Celestial Reference Frame (HCRF)
230:International Astronomical Union
174:International Astronomical Union
35:International Astronomical Union
1546:Astronomical coordinate systems
557:, Berlin: Springer, p. 1,
47:Catalogues of Fundamental Stars
423:reference frames, the axes of
1:
890:. US Naval Observatory (USNO)
1279:Astronomy & Astrophysics
1227:Astronomy & Astrophysics
1171:Astronomy & Astrophysics
263:earth orientation parameters
155:extra-galactic radio sources
140:Reference systems and frames
37:(IAU). Its origin is at the
1310:10.1051/0004-6361/202243483
1257:10.1051/0004-6361/201832727
1201:10.1051/0004-6361/201832916
1050:10.1051/0004-6361/202038368
411:celestial reference frame (
399:celestial reference frame (
372:celestial reference frame (
360:celestial reference frame (
283:galactocentric acceleration
1572:
1136:Astronomy and Astrophysics
1019:Astronomy and Astrophysics
974:10.1088/0004-6256/150/2/58
583:Astronomy and Astrophysics
31:celestial reference system
29:) is the current standard
1415:Overview of ICRS and ICRF
1394:. IERS Technical Note 34.
687:10.1017/S0074180900086149
1420:1 September 2012 at the
954:The Astronomical Journal
191:Radio wavelengths (ICRF)
1445:4 February 2012 at the
1301:2022A&A...667A.148G
1249:2018A&A...616A...2L
1193:2018A&A...616A..14G
1041:2020A&A...644A.159C
595:1995A&A...303..604A
859:. NASA. Archived from
614:. US Naval Observatory
278:
51:equatorial coordinates
1432:19 April 2014 at the
1427:IERS Conventions 2003
276:
212:of approximately 250
91:extragalactic sources
772:Astronomical Journal
345:Hipparcos catalogues
314:) and 8.4 GHz (
293:) and 2.3 GHz (
208:. It had an angular
172:In August 1997, the
167:milliarcsecond (mas)
134:astronomical objects
1556:Frames of reference
1461:ICRS Product Center
1452:General information
1086:. Paris Observatory
966:2015AJ....150...58F
927:2010AAS...21546906B
851:Steigerwald, Bell.
784:1998AJ....116..516M
323:Optical wavelengths
863:on 3 December 2020
279:
255:mean squared error
114:general relativity
1454:on the ICRS from
97:) observed using
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1447:Wayback Machine
1434:Wayback Machine
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921:. AAS: 469.06.
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470:References
449:Astrometry
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