Inconsistent times for ancient eclipses with DE406
Thomas Oct 31 4:18 PM
Hi,
I'm looking at a few ancient lunar eclipses with GUIDE8.
When it uses the default 'full ELP' I can select a time
close to the desired eclipse (say 10 Apr -665), open
the 'More info' box for the moon, click on one of the
listed eclipse phases, e.g. 'Umbra entered', and GUIDE
will switch to that time. Going forward in time with the
animation dialog will show the umbra entering the moon's
disk one or two minutes later, which is fine.
However, when I am reading the ephemeris data from the
DE406 file (UNIX.406 from the Willmann-Bell CD), I
need to go forward 23 minutes until I see the shadow
appear.
In this specific example, the 'More info' box says
'Umbra entered 10 Apr -665 15:41 UT'
regardless whether ELP or DE406 is used, but in the
graphics the umbra starts to appear at 15:43:37 UT
if ELP is used (OK) and at 16:05:37 UT if DE406 is
used (not OK).
This problem seems to exist for all lunar eclipses
and all phases in the distant past. The discrepancy
becomes smaller if I get closer to the present.
Running the 2 October 2004 version of GUIDE.
Thanks,
Thomas