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Re: How to calculate daily advance of GHA Aries?
From: Ian Gifford
Date: 2025 Aug 16, 10:54 -0700
Ian Gifford 42° 38' N, 71° 24' W
From: Ian Gifford
Date: 2025 Aug 16, 10:54 -0700
Hi Marc,
Have you tried asking your favorite AI?
Not sure I completely understand your ask but here's Grok4's take:
"The daily advance of GHA Aries (approximately 59.139') is derived from the tropical year's length (365.24219 solar days), yielding 366.24219 sidereal days, a sidereal/solar day ratio of 0.99726957, and thus an excess angular rotation of 0.985648° (or 59.139') per solar day; to calculate GHA Aries without almanacs for any date/time, compute the Julian Date, then Greenwich Mean Sidereal Time (GMST) using epoch-based formulas incorporating daily (0.06570982441908 hours/day) and hourly (1.00273790935) rates plus precession, add nutation correction for apparent time, and convert to degrees by multiplying hours by 15."
HTH
Ian Gifford 42° 38' N, 71° 24' W
