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Zero point of various ayanamshas

Ayanamsha (ayanāṃṡa) is defined as an offset from the tropical coordinates (longitudes) of spatial objects. Though it is extensively used in astrology, it is quite useful in astronomy too. In fact, sidereal coordinates is what you’d observe in the night-sky. This ayanamsa changes its value all the time due to precession of equinoxes. Well, what goes around comes around. So, at some point of time in history, the coordinates of tropial and sidereal longitudes were aligned perfectly. People disagree when this might’ve happened. Each one proposed his own ayanamsha. Oh, yeah, a reminder that astrology is pseudo-science!

The following table lists the dates of when the 0° Aries sidereal and tropical zodiacs is imagined to have coincided. These are called roots or zero points or zero values or zero ayanamsha year (ZAY). It is generated using the Swiss Ephemeris v2.08. All dates are in UT (Universal Time) in the form YYYY/MM/DD, HH:MM:SS. The years (YYYY) are in proleptic Gregorian (negative years are such that year 0 = 1 BCE, year –1 is 2 BCE etc.). The table is sorted in chronological order of dates. The last column gives the annual precession rate in year 2000 CE (measured in angle-seconds/year). The period of precession of earth’s axis is 25,771.5 years, i.e. the expected value is 50.2881±0.00098 sec per year (360 degrees/25771.5 years).

Python code can be downloaded here. Basically, the code does a bisection/binary search for x such that get_ayanamsha_ut(x) == 0 (i.e. root-finding algorithm). Other tables found on the internet may give slightly different values depending upon the options used (e.g. nutation, atmospheric refraction etc.)

Ayanamsha Name Julian day Gregorian date Precession
Skydram (Mardyks) 1662951.794128 –0160/11/27, 07:03:32.69 50.2880729
Galactic Equator 1665728.603029 –0152/07/05, 02:28:21.73 50.5561926
Galactic Equator (IAU1958) 1667118.376216 –0148/04/24, 21:01:45.10 50.5562714
Djwhal Khul 1706703.947897 –0040/09/11, 10:44:58.28 50.2880811
De Luce 1721212.804493 +0000/06/02, 07:18:28.23 50.2880811
Galact. Center = 0 Sag 1746340.526772 +0069/03/20, 00:38:33.10 50.2935882
Babylonian/Kugler 3 1774637.420198 +0146/09/09, 22:05:05.12 50.2876842
“Vedic”/Sheoran 1789947.113259 +0188/08/09, 14:43:05.54 50.3311468
Galactic Equator (Fiorenza) 1795284.830950 +0203/03/23, 07:56:34.05 50.2880728
Babylonian/Kugler 2 1797039.206852 +0208/01/10, 16:57:51.99 50.2876842
Babylonian/Aldebaran = 15 Tau 1801629.903355 +0220/08/05, 09:40:49.90 50.2876842
Fagan/Bradley 1802126.178230 +0221/12/14, 16:16:39.04 50.2880773
Babylonian/Huber 1802309.370338 +0222/06/15, 20:53:17.17 50.2876842
Babylonian/Britton 1805415.712799 +0230/12/17, 05:06:25.85 50.2877301
True Mula (Chandra Hari) 1805889.654892 +0232/04/04, 03:43:02.64 50.2871799
Babylonian/Eta Piscium 1807871.964835 +0237/09/07, 11:09:21.72 50.2876703
True Citra 1825183.966910 +0285/01/30, 11:12:21.03 50.2545475
Lahiri 1825399.994071 +0285/09/03, 11:51:27.72 50.2880767
Krishnamurti 1827944.579953 +0292/08/22, 01:55:07.94 50.2880811
Babylonian/Kugler 1 1833923.577734 +0309/01/05, 01:51:56.18 50.2876842
Galactic Equator mid-Mula 1840527.426194 +0327/02/03, 22:13:43.14 50.5561926
SS Citra 1847827.012937 +0347/01/29, 12:18:37.79 50.2879179
Vettius Valens 1853361.537968 +0362/03/26, 00:54:40.44 50.2877938
J.N. Bhasin 1854239.282468 +0364/08/19, 18:46:45.22 50.2880811
True Pushya (PVRN Rao) 1855769.247535 +0368/10/27, 17:56:27.03 50.3311468
Yukteshwar 1861700.433356 +0385/01/22, 22:24:01.96 50.2880811
Galactic Center (Gil Brand) 1861740.329930 +0385/03/03, 19:55:05.92 50.2935882
Raman 1863485.268065 +0389/12/12, 18:26:00.80 50.2880811
Aryabhata 1903396.789532 +0499/03/22, 06:56:55.58 50.2879179
Suryasiddhanta 1903396.812865 +0499/03/22, 07:30:31.57 50.2879179
Suryasiddhanta, mean Sun 1909045.584434 +0514/09/09, 02:01:35.09 50.2879179
Aryabhata, mean Sun 1909650.815332 +0516/05/06, 07:34:04.70 50.2879179
Aryabhata 522 1911797.740782 +0522/03/23, 05:46:43.58 50.2879249
Hipparchos 1920430.232109 +0545/11/09, 17:34:14.19 50.2876711
SS Revati 1924230.267300 +0556/04/05, 18:24:54.72 50.2879179
Usha/Shashi 1925433.895135 +0559/07/23, 09:28:59.65 50.2880811
True Revati 1926902.676632 +0563/07/31, 04:14:20.98 50.3942263
Sassanian 1927135.874779 +0564/03/20, 08:59:40.93 50.2879372
Dhruva/Gal.Center/Mula (Wilhelm) 1946834.824643 +0618/02/25, 07:47:29.19 52.5166881