Re: [BAA Comets] SWAN25F this morning. Nick James 07 Apr 2025 06:39 UTC

Peter,

There is definitely something odd about the PCCP ephemeris. David Moore
pointed this out as well on comets-ml. I get the following for 970 from
the PCCP:

2025 04 07 05     23 32 59.0 +25 32 08

and I get this from the Findorb using all the available astrometry
(taken from the PCCP):

2025 04 07 05     23 33 06.9 +25 33 25

The actual position I measured this morning is right on the predicted
position from Findorb. The PCCP ephemeris claims the same arc and is
using the same astrometry but clearly something has gone wrong somewhere.

Also, the uncertainty maps on the PCCP are wrong, showing potential
position errors of almost 20 arcmin.

I assume that, at some point, the brightest comet in the sky at the
moment will get a proper designation. Until then, the best source for an
ephemeris is Bill Gray's page here:

https://projectpluto.com/neocp2/summary.htm

Click on SWAN25F to get an ephemeris.

Nick.