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7e89ca6cda
I wrote a quick Python program based on an original reference
paper defining the galactic orientation system.
It generates a rotation matrix from first principles
that matches one inside the NOVAS function equ2gal(),
within the expected 2.3 arcsecond difference between
ICRS and EQJ.
NOVAS equ2gal matrix:
double ag[3][3] = {
{-0.0548755604, +0.4941094279, -0.8676661490},
{-0.8734370902, -0.4448296300, -0.1980763734},
{-0.4838350155, +0.7469822445, +0.4559837762}};
This program's generated matrix:
B1950 = 1949-12-31T22:09:21.346Z
-0.0548624779711344 0.4941095946388765 -0.8676668813529025
-0.8734572784246782 -0.4447938112296831 -0.1980677870294097
-0.4838000529948520 0.7470034631630423 0.4559861124470794
Also added some JPL Horizons test data to confirm
conversion back and forth between EQJ and GAL, which
I will use for future tests.
37 lines
2.1 KiB
Python
Executable File
37 lines
2.1 KiB
Python
Executable File
#!/usr/bin/env python3
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#
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# galeqj_matrix.py - Don Cross - 2021-06-06
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#
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from astronomy import Pivot, Time, Rotation_EQJ_EQD
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def PrintRot(rot):
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for i in range(3):
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print('{:20.16f} {:20.16f} {:20.16f}'.format(rot.rot[i][0], rot.rot[i][1], rot.rot[i][2]))
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if __name__ == '__main__':
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# This program is a sanity check that I understand galactic coordinates.
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# Compute the GAL/EQJ rotation matrix from
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# the original paper at:
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# https://watermark.silverchair.com/mnras121-0123.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAAAqowggKmBgkqhkiG9w0BBwagggKXMIICkwIBADCCAowGCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQM-h6li-3fYbw16GYKAgEQgIICXRrk54M4D9ltWJzbTRkLJ4Hb3fA4I1rbZZY7AWQlxDU7rZapZ0X7GfQWFlpffxZ-n1MULG121w6MHMZZuugksNGCqhU_8tBrNh3J1WDdLT0kig__6h72D-2ceJwydiARM-6bYd6S-z_CqScXBH6QsU8LflzPnpLz7OtfgEQQVN28ePPO2Box00NC5Sthh0Ouv06e-CyRb3ig2xP-WWP2QeGElCxJicnaDew8BUyofEHKpebe3d-Io_gXZeV7NHV1gIDTXLEp0UpM_KB9nmh39pCr4AW9zd-0j5qUlkC3TqNRlt40WuwDJn-cxFpY4O3hPtBvPmUKqspvtRP6YiqXeuCbQ6uw4OG9xcf7G39D387TeSjgGoeZRPkc0ZhpryawudLiHpXualt_uw8ws8--tAO5aUWVGL_oM2jzLEl7WVvS8jbYxXFY6GRPNBGZeDpYCP0hfXgogG305sLSWYtejlBdYECf1oJ1h_jC7HHfxI2xykD7EwI5tlRPKmNKcADJWS8Wf8zbwIE50ZB-eV1miTpBEFa6KnpD-m34k4-6dNOX9k0ALSMPOOag3o3-RGoeLdMrvqFtENM84Blo-OOADNMU5Mmo2UCjl83onZ83TdlJvSy-e2Z49i1vLScvFZlePdwJArcitb44dR1xfsbsLIR7ApcDCuF_ke96Sc3FkOOkFqM1waQZP2zuiyOr4Jg_6IFyLV5aO-2ocGoY4UkED5RzeNVSIiVC3r2QyhG51lD90ABO7LQ7RWXnsZV915Bkohh5fKIjvNM0ejAm87uMzsYhlzIIind9U6DqnCde
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# Equatorial B1950.0 coordinates of the Galactic North Pole:
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ra = 12.0 + 49.0/60.0
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dec = +27.4
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# Orientation angle for the zero lon/lat point in galactic coordinates:
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theta = 123.0
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# Calculate the B1950.0 epoch based on:
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# https://en.wikipedia.org/wiki/Epoch_(astronomy)
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b1950 = Time.FromTerrestrialTime(2433282.4235 - 2451545.0)
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print('B1950 = {}'.format(b1950))
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# Create a rotation matrix to convert from J2000 equatorial to B1950 equatorial.
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rot = Rotation_EQJ_EQD(b1950)
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# Pivot using the ra/dec angles for the galactic north pole.
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rot = Pivot(rot, 2, -15*ra)
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rot = Pivot(rot, 1, -(90-dec))
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rot = Pivot(rot, 2, theta-180)
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PrintRot(rot)
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