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Re: Lunar4.4. vs Frank's online calculator
From: Paul Hirose
Date: 2023 Apr 26, 23:41 -0700

I duplicated the results of Modris Fersters with Lunar 4.4 (DE441 ephemeris). time 2023-04-02 18:40:00.00 UT1 2023-04-02 18:41:09.48 TT +1m09.48s delta T position 24°00.00' +56°00.00' east lon, north lat 0.0 meters (0 feet) above ellipsoid atmosphere 10.0 C (50.0 F) at observer 1010.0 mb (29.83″ Hg) air pressure 50.0% relative humidity Moon 44°11.89' computed unrefracted center altitude 15.02' unrefracted semidiameter 0.98' refraction 44°27.90' apparent upper limb altitude 148°17.17' predicted azimuth Venus 16°52.49' computed unrefracted center altitude 3.14' refraction 16°55.63' apparent center altitude 278°45.19' predicted azimuth My program recommends Moon upper limb and Venus far limb. It also has a "center of light" option. But in this case, Venus phase angle is 58°, so I don't think there's much error if observe Venus center and ignore phase. The easy way is to select "center" for the Venus distance limb (in the program main window). Then the output omits a correction for Venus SD: topocentric apparent Moon to Venus angle: 104°03.44' center to center, unrefracted 3.25' refraction 104°00.19' center to center, refracted -15.02' Moon near limb refracted SD 103°45.17' computed Moon to Venus The last line is identical to his value. But is it correct? You can get azimuth, altitude, and angular diameter from the JPL Horizons online ephemeris. (Does not give semidiameter.) Apply refraction to the altitudes, then compute separation angle. Subtract Moon SD. (Lunar 4.4 says refraction has no effect on SD at 0.01' precision.) https://ssd.jpl.nasa.gov/horizons/app.html#/ Careful - observer coordinate order is longitude, latitude, height. There is an option to apply standard refraction, but I have never used it. I would investigate this myself, but it's time to go to bed. -- Paul Hirose sofajpl.com

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