Sidereal Time formula / 1 second divergence 1 by Petr9 Hello, I'm trying to calculate exact Sideral Time (ST0). I found several formulas based on Julian Dates (JD and JD0) which differ very slightly: === T = (JD0 - 2451545.0)/36525; ST0 = (6.697374558) + (2400.051336 * T) + (0.000025862 * T*T); === T = (JD0 - 2451545.0)/36525; ST0 = (6.697374558) + (2400.05133691 * T) + (0.000025862 * T*T) - (0.0000000017 * T*T*T); === D0 = JD0 - 2451545.0; T = (JD - 2451545.0)/36525; ST0 = 6.697374558 + (0.06570982441908 * D0) + (0.000026 T*T); === All of these formulas give almost the same results rounded to 0.000x seconds (00:00:00.000x). But if I compare the results with astro.com or Morinus software, there is almost always +-1 second divergence (00:00:0x) eg: May 9, 1983 (00:00UT) ST0 15:04:59.081x (all formulas) ST0 15:04:58 (astro.com) ST0 15:04:57 (morinus) eg: December 16, 2009 (00:00UT) ST0 05:39:04.144x (all formulas) ST0 05:39:05 (astro.com) ST0 05:39:05 (morinus) Do you know, if there is another formula; or something wrong, with these formulas, please? === EDIT: I know it's just 1'' second divergence, but this 1 second is causing bigger divergences in further calculations - especially in Primary Directions to angles MC/ASC (1'' in ST0 <=> cca 15'' in RA arcs <=> cca 1,5 days in PD) I would be thankful for any help. Quote Thu Aug 03, 2017 9:58 pm
2 by Petr9 Maybe I figured it out. Astrodienst and Morinus is (probably) using Apparent Sidereal Time, which takes into account nutation and differs ±1.2s from Mean Sideral Time. I found additional equations and corrections for nutation and now it calculates the same results. === https://horoscopes.astro-seek.com https://horoscopes.astro-seek.com/traditional-astrology https://es.astro-seek.com (ES) https://de.astro-seek.com (DE) https://ru.astro-seek.com (RU) https://it.astro-seek.com (IT) https://tr.astro-seek.com (TR) Quote Thu Aug 10, 2017 8:23 am