ASTROMETRIC UPDATE:
OCCULTATION BY (86) SEMELE - 2001 SEPTEMBER 20
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[Prediction by Edwin Goffin]
[Prediction using OCCULT software]
Goffin's path runs centrally across the North Island of New Zealand from the west. The path given by Occult lies slightly to the south across Wanganui, Palmerston North and Hastings.
UPDATE: 18 September 2001
This prediction update has been computed by Steve Preston of Medina, Washington (state) in the United States based on astrometry from Ron Stone of the US Naval Observatory - Flagstaff Station supplemented with data from the AstDys database. The UCAC position of the target star has been used.
Summary:
This updated path lies around one path width to the south of that given by Goffin with little difference in expected time. The path crosses the northern tip of the South Island and the southern parts of the North Island around 7:16 UT - just at the end of local twilight. Nelson and Wellington lie near the southern edge of the path with Wanganui and Hastings near the north edge. The error tolerance of this calculation is such that observations between the Bay of Plenty and Christchurch stand a reasonable chance of success.
Additional details of this and other events are available at Steve Preston's website at http://www.oz.net/~stevepr/Asteroids/asteroid.htm
THE EVENT AT ONE GLIMPSE:
- Date and approx. UT time of event: September 20 : 7:16 UT
- Magnitude of target star: 11.90
- Magnitude drop [mag]: 2.5
- Estimated maximum duration [s]: 10.3
- Path description: See above.
- Goffin's original chart reference: A01_0912
The Occultation Path:
- Approximate width [km]: 124
- Uncertainty [path widths]: +/- 0.70 (1 sigma)
- Map: See below
Data for the target star:
- Name: TYC 6847-00161-1
- Constellation: Sagittarius
- J2000 position [h,m,s; o,',"]: 18h 10m 47.7817s; -25o 33' 38.681"
- Position source: UCAC
- Estimated accuracy ["]: 0.040" (0.031", 0.030")
- V mag [mag]: 11.90
- Remarks:
- The target star is in western Sagittarius. It lies 28' northeast of the globular star cluster NGC 6553 and 1.9 degrees southeast of the Lagoon Nebula - M 8.
Data for the minor planet:
- Number, name: (86) Semele
- Approx. diameter [km]: 127
- Source of used astrometry: US Naval Observatory - Flagstaff Station (Ron Stone), AstDys
- Number of used observations: 418
- Number of rejected observations: 45
- Time covered by the observations: 1903 08 27 - 2001 09 08
Data for the event:
- UT date and time of least geocentric approach: 2001 September 20, 7:15.0 UT
- Approx. V mag of minor planet at event [mag]: 14.24
- Geocentric parallax of minor planet ["]: 3.08
- Magnitude drop [mag]: 2.5
- Estimated maximum duration [s]: 10.3
- Apparent motion of minor planet ["/h]: 21.54
- Angular distance to moon, phase of moon [deg,%]: 56, 12%
- Update computed by: Steve Preston, Medina, Washington, USA. (OrbFit).
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.
Use these links for further information:
[Planetary Occultations]
[Using the Predictions]
[Observing Details]
[Timing Details]
[Reporting Details]
[Report Form]
[Asteroid Occultation Results]
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