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Re: Lunar4.4. vs Frank's online calculator
From: Paul Hirose
Date: 2023 Apr 29, 13:52 -0700
From: Paul Hirose
Date: 2023 Apr 29, 13:52 -0700
Output from JPL Horizons:
Observer: 24.0, 56.0, 0.0 {E-lon(deg),Lat(deg),Alt(km)}
No refraction.
Time scale UTC.
Date__(UT)__HR:MN Azi____(a-app)___Elev Ang-diam TDB-UT
********************************************************************
Venus
2023-Apr-02 18:40 278.753244 16.874826 14.14047 69.185651
Moon
2023-Apr-02 18:40 148.286353 44.198289 1802.692 69.185651
https://ssd.jpl.nasa.gov/horizons/
Topocentric unrefracted distance, center to center:
104.05726° Horizons
104.05726° Lunar 4.4
Perfect agreement so far. To be strictly correct, the UT1-UTC value
-0.001651 s can be input in the Lunar time window. However, at this
precision the small difference between UT1 and UTC has no effect on
distance because its rate is only -0.0057° per minute.
Compute refraction with the SOFA refco routine (Lunar 4.4 uses the
Cassini refraction model):
http://www.iausofa.org/2021_0512_C/sofa/refco.c
(pressure = 1010 mb, temperature 10 C, relative humidity = 0.5,
wavelength .55 microns)
0.05232° Venus refraction in altitude
0.01654° Moon
Horizons az/alt, adjusted for refraction:
278.75324° 16.92714° Venus
148.28635° 44.21483° Moon
refracted distance, center to center:
104.00306° Horizons
104.00308° Lunar 4.4
The discrepancy is equivalent to 0.07″, and is due to the different
refraction models. Refraction also decreases Moon semidiameter, about
0.00010° in this case. Lunar 4.4 applies that correction. Both programs
agree that topocentric unrefracted SD = 0.25037°.
--
Paul Hirose
sofajpl.com
