This prediction update is supplied by Jan Manek of the Stefanik Observatory, Prague, and is based on USNO/Flagstaff astrometry for the minor planet and the TAC star position.

Summary:

This calculation gives no path shift with occultation time ~0.4 minutes later compared to Edwin Goffin's nominal prediction.

THE EVENT AT ONE GLIMPSE:

• Date and approx. UT time of event: January 29, 2000 @ 18:52 UT
• Magnitude of target star: 8.8
• Magnitude drop [mag]: 2.2
• Estimated maximum duration [s]: 12.8
• Goffin's original chart reference: A00_0107.PS.GZ

• Approximate width [km]: 160
• Uncertainty [path widths]: 1
• Uncertainty in time [s]: 15
• Map: See below
• Remarks:Uncertainties are given on basis of nominal star position errors and expected asteroid positional accuracy.
• Circles along the path are OCCULT calculated exact centerline points !!!. (Therefore the path is nearer to Brisbane than the path boundary lines may suggest).

• Name: PPM 227865 = SAO 158173 = TYC 5556 00903 1
• Constellation: Virgo
• J2000 position [h,m,s; o,',"]: 13h 48m 02.761s; -11^o 28' 50.14"
• Position source: TRC1.0
• Estimated accuracy ["]: 0.04" (0.03", 0.03")
• V mag [mag]: 8.79
• B-V [mag]: +0.99
• Remarks: TYCHO gives quality flag 3 (=high) with 'no duplicity' flag.
• Target star is in southern Virgo, about 5.6 degrees EAST of 1.1 mag star alpha Virginis = Spica. There is a 5.5 mag star SAO 158152 = 86 Vir about 1.1 degrees SSW of the target. Be careful as there is a 11.2 mag star GSC 5556.0988 only 1.1' east of the target - this star is only slightly fainter than the asteroid itself.

• Number, name: (20) Massalia
• Approx. diameter [km]: 151 km
• Orbit source: calculation Manek
• Source of used astrometry: USNO/Flagstaff (Ron Stone), TMO (Bill Owen)
• Number of used observations:27 USNO, 44 TMO
• Number of rejected observations: 2 USNO
• Time covered by the observations: 1997 05 11 - 2000 01 12
• Rms residuals ["] (RA,DE): 0.08", 0.06"
• Estimated positional accuracy at epoch of event ["]: 0.08"

• UT date and time of least geocentric approach: 2000 January 29 - 18:54:57 UTC
• Approx. V mag of minor planet at event [mag]: 10.8
• Geocentric parallax of minor planet ["]: 4.552
• Magnitude drop [mag]: 2.2
• Estimated maximum duration [s]: 12.8
• Apparent motion of minor planet ["/h]: 30.24
• Angular distance to moon, phase of moon [deg,%]: 25, 37%

Centerline path coordinates:
                                       Altitude
  E. Longitude    Latitude     U.T.    star  sun
   ........ shortened ..........................
   + 92 00 00   -  0 42 01   18 47 04   25   -69
   + 94 00 00   -  1 25 03   18 47 13   27   -67
   + 96 00 00   -  2 09 21   18 47 23   29   -65
   + 98 00 00   -  2 54 50   18 47 33   31   -63
   +100 00 00   -  3 41 27   18 47 45   33   -62
   +102 00 00   -  4 29 09   18 47 57   35   -60
   +104 00 00   -  5 17 51   18 48 10   38   -58
   +106 00 00   -  6 07 28   18 48 23   40   -56
   +108 00 00   -  6 57 55   18 48 37   42   -54
   +110 00 00   -  7 49 09   18 48 52   44   -52
   +112 00 00   -  8 41 02   18 49 07   46   -49
   +114 00 00   -  9 33 29   18 49 23   48   -47
   +116 00 00   - 10 26 26   18 49 40   50   -45
   +118 00 00   - 11 19 45   18 49 56   53   -43
   +120 00 00   - 12 13 22   18 50 14   55   -41
   +122 00 00   - 13 07 09   18 50 32   57   -39
   +124 00 00   - 14 01 00   18 50 50   59   -37
   +126 00 00   - 14 54 50   18 51 08   61   -34
   +128 00 00   - 15 48 32   18 51 27   63   -32
   +130 00 00   - 16 42 00   18 51 46   65   -30
   +132 00 00   - 17 35 08   18 52 06   66   -28
   +134 00 00   - 18 27 50   18 52 25   68   -26
   +136 00 00   - 19 20 00   18 52 45   70   -24
   +138 00 00   - 20 11 33   18 53 04   71   -22
   +140 00 00   - 21 02 24   18 53 24   72   -19
   +142 00 00   - 21 52 27   18 53 44   74   -17
   +144 00 00   - 22 41 39   18 54 03   75   -15
   +146 00 00   - 23 29 53   18 54 23   75   -13
   +148 00 00   - 24 17 07   18 54 42   76   -11
   +150 00 00   - 25 03 16   18 55 01   76    -9
   +152 00 00   - 25 48 17   18 55 21   75    -7
   +154 00 00   - 26 32 07   18 55 39   75    -5
   ........ shortened ..........................

Calculator: Jan Manek

Set out below is a more detailed finder chart for the target star. The numbers are SAO catalogue identifiers for the stars and 86 Vir is identified. The target star is indentifed by the cross near the centre of the chart. Note the close companion to the east (left) of the target star. This chart represents the bulk of the area of Goffin's detailed chart but to a deeper magnitude limit. Chart prepared by Jan Manek.

IMPORTANT NOTE!

Astrometric updates such as these should not be taken as definitive, but rather only as an indication of where the true track may lie relative to the original predicted track. Observers must bear in mind that later astrometry, in which the target star is measured in the same field as the asteroid, may still reveal substantial changes to the predicted track and time of the event. For this reason it is most important that observers far from the predicted track still monitor the event.