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.

The ICRF2, submitted for adoption by IAU at the XXVII General Assembly (august 2009), contains precise positions of 3414 compact radio astronomical sources, more than five times the number as in ICRF1.

It used instead a smaller number of extragalactic radio objects measured by VLBI with much higher accuracy and established celestial coordinate axes independent of equator, ecliptic, and epoch.

The ICRF3 was adopted as the new fundamental celestial reference frame by the IAU during its XXXth General Assembly in Vienna, 30 August 2018, replacing the ICRF2 as of 1 January 2019.

2015年7月24日 · We present the second realization of the International Celestial Reference Frame (ICRF2) at radio wavelengths using nearly 30 years of Very Long Baseline Interferometry observations. ICRF2 contains precise positions of 3414 compact radio astronomical objects and has a positional noise floor of ~40 μ as and a directional stability of the frame ...

The Second Realization of the International Celestial Reference Frame (ICRF2) was adopted at the XXVII General Assembly of the International Astronomical Union (IAU) in Rio de Janeiro, Brazil as Resolution B3.

Further, the ICRF2 is found to have a noise floor of only ≈ 40 µas, some 5−6 times better than ICRF1, and an axis stability of ≈ 10 µas, nearly twice as stable as ICRF1.