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Re: Calculating nutation with a spreadsheet?
From: Paul Hirose
Date: 2025 Jun 26, 22:14 -0700
From: Paul Hirose
Date: 2025 Jun 26, 22:14 -0700
> *From: *Brian Villmoare > *Date: *2025 Jun 26, 17:02 -0700 > > Right now I am running it against Stellarium, just spot-checking random > dates. Using the IAU 2006 Precession model and the IAU-2000B, 10-term > nutation model I seem, at least preliminarily, to be able to get within > ~.5 arcseconds. But then it just became a question of whether I could > improve it - it seemed like I should be able to get it better, based on > what Paul said. But maybe that's all that can be obtained with just > Excel and those two models (and the "frame-bias" matrix). Frame bias corrects for the misalignment between the J2000 frame and ICRS. The latter was intended to be close to the former, but there's a small discrepancy. It's 10 - 20 mas and can be disregarded at 0.1" precision. Any troubleshooting of the error in your spreadsheet depends on what coordinates you're looking at. Geocentric apparent equatorial vs. topocentric horizontal, for instance. And are you sure Stellarium is right? One good test is the stellar reduction example in the Astronomical Almanac. It uses the 2006/00A precession / nutation model. I use the simplified B nutation model in my Lunar software and get this: geocentric apparent equinox RA, dec 14h40m52.33093s -60°54'21.916" Lunar 14h40m52.3309 -60°54'21.915" Almanac https://archive.org/details/binder1_202003/page/n189/mode/1up?view=theater -- Paul Hirose sofajpl.com
