NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

HOME

Re: Introduction to Modern Astrometry
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

What is NavList?

NavList is a community devoted to the preservation and practice of celestial navigation and other methods of traditional position-finding. We're a group of navigators, navigation enthusiasts and hobbyists, mathematicians and physicists, and historians interested in all aspects of navigation but primarily those techniques which are non-electronic.

To post a message, if you are already signed up as a NavList member, start a new discussion or reply to any posted message and use your posting code (this is a simple low-security password assigned when you join). You may also join by posting. Your first on-topic messsage automatically makes you a member, and a posting code will be assigned and emailed to you for future posts.

Uniquely, the NavList message boards also permit full interaction entirely by email. You can optionally receive individual posts or daily digests by email, and any member can post messages by email (bypassing the web site) by sending to our posting address which is "NavList@NavList.net". This functionality is similar to a traditional Internet mailing list: post by email, read by email, reply by email. Most members will prefer the web interface here for posting and replying to messages.

NavList is more than an online community... more about that another day.

© Copyright notice: please note that the rights to all messages and posts in this discussion group are held by their respective authors. No messages or text or images extracted from messages may be reproduced without the explicit consent of the message author. Email me, Frank Reed, if you have any questions.

Subject:
Author:
Start date:	(yyyymm dd)
End date:	(yyyymm dd)

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

NavList

What is NavList?

Join / Get NavList ID Code

Retrieve a NavList ID Code

Email Settings

Custom Index

Add Images & Files
Name or NavList Code:	Email:

Name:
	(please, no nicknames or handles)
Email:

NavList ID Code: