RE: date error occurs during April 2004

[Thomas Droege <tdroege2@earthlink.net>]

I have been looking at the data disks and other than the RA correction, I
can find nothing to pin down where there is a date problem.  It is
suspicious that the problem seems to have started when I went to 2 degree
steps in Dec.  

The problem is that I can imagine setting all the clocks wrong.  What I
can't imagine is setting them back without noticing that they were all an
hour off.  OK, I can imagine not noticing that one was an hour off.  The
computers die from time to time and sometimes in horrible ways that require
resetting the clocks.  But they seldom all three die at once.  Even as a
result of thunderstorms.  So it would be really helpful to find out if this
is just a TOM2 problem or whether it is also a TOM1 and TOM3 problem.  

From time to time the RA drive does not stop when it is supposed to.  For
example if I do not get to the computer to turn it off at dawn.  There can
be an overflow, the computer crashes, and the RA drive keeps going.  This
happened on June 3.  This stretches the RA drive cable and could cause the
RA correction to jump in an arbitrary way.  So the RA correction is not a
perfect check.   On April 3 We changed operation so that we stepped in 2
degree increments.  Thus there should be 2 measurements of each object
measured untill I switched back to 4 degree steps on 5 May.  Pm 5 ,au 

More data would help to pin down the days that have a problem.  

Tom Droege


> [Original Message]
> From: Stupendous Man <richmond@stupendous.cis.rit.edu>
> To: <tass@listserv.wwa.com>
> Cc: <mwrsps@rit.edu>
> Date: 6/12/2004 10:44:48 AM
> Subject: date error occurs during April 2004
>
>
>   Following Gary Billings' idea of using asteroid positions
> to check the date in Mark IV data, and Richard Miles' suggestion
> of 739 Mandeville during April, 2004, I find the following:
>
>         real date and time                  Mark IV date and time
>
>     Apr  2 UT (JD 2453096.86)       Mark IV position matches JPL ephemeris
>
>     Apr 14 UT (JD 2453109.82)       Mark IV position from "JD 2453108.82"
>                                             matches JPL ephemeris
>   
>     Apr 15 UT (JD 2453110.83)       Mark IV position from "JD 2453109.83"
>                                             matches JPL ephemeris
>     
>
>     Apr 26 UT (JD 2453120.79)       Mark IV position matches JPL ephemeris
>
>
>
>   In all these detections, the Mark IV database showed detections
> at the asteroid's position only on the given date and time; in other
> words, I wasn't confusing ordinary stars for the asteroid.
>
>   So, I conclude that the Mark IV database has an "off-by-one-day"
> error for _part_ of the month of April, 2004.  This suggests to me
> a problem with the clocks on the computers, rather than with the software
> which calculates JD. 
>
>   I need to write a script to go through _all_ the Mark IV data
> and search for asteroids in order to see if this is the only
> date-and-time problem in the database.  Michael Sallman's
> database interface will help greatly.
>
>   More later.
>
>                                              Michael Richmond
>