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> *From: *Bill Ritchie
> *Date: *2025 Aug 7, 14:45 -0700
>
> However, when I asked Microsoft’s Copilot AI, and then pressed for a
> more accurate answer, it differed from the above by 38” and was 61
> minutes later, allegedly using JPL. I quote …
>
> “*Precise Geocentric Separation: Venus–Jupiter Conjunction, 12 August 2025*
>
> For your arcsecond-level comparison, here's the refined data:
>
> *🪐 Closest Approach Details*
>
>   * *Date*: 12 August 2025
>   * *Time (UT)*: *07:40 UTC*
>   * *Minimum Geocentric Separation*: *51 arcminutes 0 arcseconds* →
>     Equivalent to *3060 arcseconds*
>   * *Right Ascension (both)*: 06h 59m 30s
>   * *Declination*:
>       o Venus: +21°48′00″
>       o Jupiter: +22°39′00″
>   * *Constellation*: Gemini
>   * *Angular distance from Sun*: ~35°
>   * *Source ephemeris*: DE430 (JPL)”

Maybe the word "appulse" would have produced the time of closest approach.

Copilot appears to give coordinates with respect to the ICRS
(approximately, the mean equator and equinox at 2000.0) instead of the
true equator and equinox of date. The discrepancies vs. my computation
are respectively 1'09" and 22'38". A precise evaluation is not possible
due to insufficient RA precision. At this declination, one second of RA
is the same size as 14 seconds of declination. (A good rule of thumb is
to give RA one more digit of precision than dec.)

Coordinate frame doesn't affect the computation of angular separation.
However, a minute of arc error is excessive from a JPL ephemeris. You
could do better with a simple long term ephemeris like PLAN94 in the
SOFA library (algorithm due to Simon, Bretagnon, Chapront,
Chapront-Touze, Francou, Laskar). PLAN94 is within 2" of the JPL DE430.

Venus
6h59m30s   +21°48′00″ Copilot
6h59m34.8s +21°48'14" DE430 (ICRS)
6h59m34.9s +21°48'14" PLAN94 (ICRS)
7h01m07.1s +21°46'09" DE430 (true equator & equinox)

Jupiter
6h59m30s   +22°39′00″ Copilot
6h59m35.0s +22°39'55" DE430 (ICRS)
6h59m34.5s +22°39'57" PLAN94 (ICRS)
7h01m07.9s +22°37'50" DE430 (true equator & equinox)

For Jupiter, PLAN94 is within 6" of DE430.

Copilot puts both planets west and south of my coordinates. It says
separation is 51′ 0″. My center to center distance is 51'41" at the same
time. It's not clear whether Copilot calculated between centers or limb
to limb. (Semidiameters are Venus 7", Jupiter 17".) It says separation
from sun is ~35°, which is within a degree of my value. Venus phase
angle is 55° (gibbous) and has no significant effect at this precision.

My UTC times:
05:30:10 ecliptical longitude conjunction
06:39:11 minimum separation
07:40:54 RA conjunction (ICRS)
07:44:10 RA conjunction (true equator of date)

--
Paul Hirose
sofajpl.com

   

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