| | ICRS Narrative (Site not responding. Last check: 2007-10-09) |
 | | The equinox, therefore, is a direction in space along the nodal line defined by the intersection of the ecliptic and equatorial planes; equivalently, on the celestial sphere, the equinox is at one of the two intersections of the great circles representing these planes. |
 | | Furthermore, because these radio sources are very distant extragalactic objects (mostly quasars) that are not expected to show measurable intrinsic motion, a reference frame defined by VLBI positions should be "more inertial" (less subject to spurious rotation) than a reference frame defined by galactic objects such as stars or pulsars. |
 | | International Celestial Reference Frame (ICRF) is a catalog of adopted positions of 608 extragalactic radio sources observed with VLBI, all strong (>0.1 Jy) at S and X bands (wavelengths 13 and 3.6 cm) [9]. |
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