Greetings all Ted Molczan queried an observation of mine on 20 Jan 1997 as follows: >Greg Roberts wrote: >>Observation on 20th Jan 1997 from my usual site of 96072A as follows: >>#24680 96072A 19h52m59.3s UT RA 11h47.7m,Dec -40d19' (J2000) >>There may be a slight timing error-I had no time signals for about 10 minutes >>either side of the observation so had to stop the one stopwatch against my >>other stopwatch which I use as a "clock". This earlier had an error of about >>1.5 seconds and I have corrected the time above for this. >Your position appears to be very accurate, as usual, but the time is >about 2.9 s early, relative my 97018.858 elset, as judged from this >ephemeris: > TIME %I Mv AZ EL R.A. DEC FE VANG RANGE ALT >-------- -- ---- --- -- ----- ------ -- ---- ----- ----- >19:52:57 59 6.4 129 14 11:51 -40:50 4 0.17 2004 764 >19:52:58 59 6.4 129 14 11:51 -40:44 4 0.17 1999 764 >19:52:59 59 6.4 129 14 11:50 -40:38 4 0.17 1994 763 >19:53:00 60 6.4 129 14 11:49 -40:32 4 0.17 1990 763 >19:53:01 60 6.4 129 14 11:48 -40:26 4 0.17 1985 762 >19:53:02 60 6.4 129 14 11:48 -40:20 4 0.18 1981 762 >19:53:03 60 6.4 128 14 11:47 -40:14 4 0.18 1976 762 >19:53:04 60 6.4 128 14 11:46 -40:08 4 0.18 1971 761 >I would have to multiply the decay rate over the past 2 days by a factor >of about 3, to account for this, but that is virtually impossible, since >the sun has remained quiet during that period. >The difference also is well outside the uncertainty in the mean motion. >One possible explanation - could you have applied the 1.5 s correction >in the wrong direction, i.e subtracted, instead of added? YES , Ted, I am an idiot - I did SUBTRACT so the CORRECT TIME should be 3 seconds later, ie 19h 53m 02.3s UT. Thanks for pointing it out - now I can understand why they retire old crocks like me when they get too old! >>#24681 96072B -- looked for it but not seen.Shadow entry was predicted for 8 >>degrees and I cannot access this elevation from my site using my 5 inch >>tracking telescope so I tried 7x50 binoculars. >The situation may have been even worse. My ephemeris for your site indicates >shadow entry (mid-point of penumbra) at 6 deg. It would have reached the >umbra at about 7 deg. Interesting. I have been using several prediction programs for this current series of tracking and the one I have used mainly is SKYMAP510 and the map shows shadow entry at 8 degrees. Similarly for the observation last week when you stated that the observation was in shadow but again SKYMAP510 showed it still illuminated. I havent checked my own prediction program which does shadow entry but I do recall that to fit actual observations of shadow entry I went another 0.9 degrees into shadow for the actual "cut-off" point. This was not a figure of my choosing- I think it originally appeared in MEMOIRS OF THE BRITISH ASTRONOMICAL ASSOCIATION Artificial Satellites where there was an article on SOLAR ILLUMINATION, by, if my memory is correct, G.E.Taylor . I can dig up full details if anyone interested. Last night cloudy so no observations. Cheers Greg