NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Introduction to Modern Astrometry
From: Paul Hirose
Date: 2023 Jul 16, 13:42 -0700
From: Paul Hirose
Date: 2023 Jul 16, 13:42 -0700
On 7/14/2023 1:06 PM, NavList Community wrote: > I'm especially interested in learning about the new > ICRS/GCRS coordinate system and how to convert to/from the traditional > coordinate systems like J2000.0. Also how to convert an apparent > position to an astrometric position in one of these new coordinate systems. Material at the SOFA (Standards of Fundamental Astronomy) site may be helpful. In particular, see "SOFA Tools for Earth Attitude" http://www.iausofa.org/cookbooks.html There's Section B of the Astronomical Almanac and the almanac glossary. https://archive.org/details/binder1_202003/page/n141/mode/2up?view=theater https://aa.usno.navy.mil/faq/asa_glossary The conversion from ICRS/GCRS to the J2000.0 frame or vice versa is straightforward since there's a fixed offset between the frames. See the Astronomical Almanac, page B51, rotation matrix B. https://archive.org/details/binder1_202003/page/n167/mode/2up?view=theater Regarding the conversion from apparent position to astrometric, that's the reverse of the normal sequence. I think it could be accomplished by iteration. Begin with a first approximation: astrometric = apparent. Convert that "astrometric" position to apparent. From the discrepancy with respect to the true apparent position, compute a correction to astrometric position and repeat the conversion. -- Paul Hirose sofajpl.com
