In the paper for my All-Sky Portable (ASP) optical catalog
(2017,PASA,34,e025), on its Figure 4, I called attention to a stellar
R=18.3 object at J100757.9+095617 which appeared only on the
1950's-epoch POSS-I plate, and was not seen there at later epochs.
Now, 8 years later, I've identified this object as being the asteroid
58227 (1993 FB26). I've generated its ephemeris from JPL/HORIZONS at
https://ssd.jpl.nasa.gov/horizons/app.html#. The ephemeris shows:
1950-Apr-17 11:00 UT 10 07 59.79 +09 56 04.7 (J2000) V= 19.158
The corresponding POSS-I photograph on plate eo74 (N490) shows:
1950-Apr-17 04:00 PST 10 07 57.96 +09 56 17.1 (J2000) V=19.047
Thus the ephemeris-calculated position is offset 29.746 arcsec from
the photographed position. The ephemeris uses data starting in 1962,
so it says, but I'm surprised that the orbit would be offset as much
as 29.7 arcsec just 12 years earlier.
The 1950's-era POSS-I plates would serve as a valuable positional
check on asteroid orbits, so I've emailed JPL with this example and
that idea.
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