International Celestial Reference Frame

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The International Celestial Reference Frame ( ICRF ) is a quasi- reference system with the barycenter of the solar system as its center. It is defined by the positions of quasars and other extragalactic objects with strong radio radiation measured with radio telescopes .

Although the general theory of relativity implies that there can be no correct reference systems around gravitational bodies, the ICRF is useful because there has been no measurable displacement of the extragalactic objects since its creation because they are extremely distant. The ICRF is currently the reference system with which the positions of planets, stars and other astronomical objects are defined.

The positions of the ICRF are obtained by VLBI , whereby at least two radio telescopes must be involved in each measurement.

ICRF1

The first version ICRF1 was adopted by the International Astronomical Union on January 1, 1998 . The ICRF1 has a noise floor of approx. 250 micro-angular seconds (µas) and an axis stability of approx. 20 µas, which represents an improvement of several orders of magnitude compared to Fundamentals Catalog 5 (FK5). The first version from 1998 contains 212 extragalactic objects that were used to define the reference system, as well as the positions of 396 other objects that are not used for the reference system. Their positions were partially adjusted in later extensions. The ICRF is the first implementation of the International Celestial Reference System (ICRS) in the radio sector.

A first expansion took place in 1999 with ICRF-Ext.1. 59 new objects were added, and existing objects received improved position data. In 2004 ICRF-Ext followed. 2 a second extension with 109 additional objects and improved position data.

ICRF2

The ICRF2 was created in 2009. ICRF2 is defined by the position of 295 radio sources , of which only 97 are also included in ICRF1 as defining sources. Together with the sources not used for definition, it comprises 3,414 objects, measured using Very Long Baseline Interferometry , it has a noise floor of 40 µas and an axis stability of 10 µas.

ICRF3

On August 30, 2018, the General Assembly of the International Astronomical Union (IAU) in Vienna decided to use the new, celestial reference frame ICRF3 as the international reference system from January 1, 2019, in order to be able to specify directions in space more precisely than before. It is based on the measurement of 4,536 extragalactic radio sources using VLBI and has an accuracy of approx. 30 µas. The objects were examined in different frequency bands: 4,536 in S / X, 824 in K and 678 in X / Ka band.

Individual evidence

  1. ↑ a b IERS Technical Note No. 35: The Second Realization of the International Celestial Reference Frame by Very Long Baseline Interferometry . International Earth Rotation and Reference Systems Service (IERS). Archived from the original on July 25, 2015. Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved April 5, 2014. @1@ 2Template: Webachiv / IABot / ww2.iers.org
  2. ↑ MVS Import: New coordinate system for space . In: scinexx | The knowledge magazine . September 3, 2018 ( scinexx.de [accessed December 1, 2018]).
  3. ↑ Julien Frouard, Megan C. Johnson, Alan Fey, Valeri V. Makarov, Bryan D. Dorland: Towards the ICRF3: astrometric comparison of the USNO 2016A VLBI solution with ICRF2 and Gaia DR1 . April 25, 2018, arxiv : 1804.10240 ( arxiv.org [PDF]).
  4. ^ IERS ICRS Center. Accessed December 1, 2018 .

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