General Info on Accuracy
The updated path descriptions are relative to my map on p. 86 of
the 1998 Feb. issue of Sky and Telescope, which gives some additional
information (expected duration, star information, etc.) in the table on
p. 87 and a finder chart for the Nausikaa event on p. 89.
The formal prediction accuracy is about a third of a path-width
for each event, making it probable that travel into the path will
considerably increase chances for seeing the occultation. The
observations used to update the prediction are the new ACT and HIP-
catalog-relative measurements at the U.S. Naval Observatory (USNO)'s
station in Flagstaff, Arizona, which predicted the Dec. 4th Artemis
occultation path to within 0.01" or 1/10th of a path width. However,
similar measurements were less successful for the Iduna occultation on
Jan. 17th, the event successfully observed from Monterrey, Mexico, 0.15"
north of the expected updated path. A similar error for Nausikaa would
be 2 path-widths and for Julia it would be 1.5 path widths. So
observers at least those distances from the updated paths are encouraged
to attempt observations.
Nausikaa path 1.2 widths south, over cen. Colo. (8:14 pm MST); Omaha
(9:14 pm CST); Peoria (9:13 pm CST); Gary & Ft. Wayne, Ind. (10:13
pm EST); Toledo & Cleveland; Erie; Binghamton, N.Y.; all
of Massachusetts (10:12 pm EST); Azores (3:08 UT Jan. 27 UT);
Morocco to Yemen (3:06 to 3:00 UT Jan. 27 UT). An expedition from
the DC area is planned probably to southern New York if the weather
forecast is for reasonably clear skies, which it may be; contact
me for details if you might be interested in joining such an effort.
Martin Federspiel's prediction information for the Nausikaa
occultation is given below; his description follows the numerical data.
(192) Nausikaa occults SAO 99095 (RA 10 23 25.436 DE +13 54 19.47),
mag. of star 8.8, 5 deg. east & a little north of Regulus
orbit from CAMC, Hipparcos, & USNO positions, star position from USNO
Minimum geocentric distance:
date: 1998 1 27 time: 3 6 21.UT; d=1.89", PW=15.01 deg, pi=4.99",
Central line for an occultation by (192) Nausikaa
(expected: path width 115 km; occ'n. dur. 9s, mag. drop 2.7)
East
Lat. Long. hh:mm:ss UT StarAlt StarAzi SunAlt SunAzi
17.09 44.93 2:59:22. ! 32.2 276.0 -8.5 106.9
19.32 38.74 2:59:59. ! 38.1 272.8 -14.6 104.9
23.19 28.08 3: 1:13. ! 47.7 265.3 -24.8 100.5
26.57 18.53 3: 2:27. ! 55.4 255.4 -33.6 95.4
29.62 9.47 3: 3:41. ! 61.5 242.1 -41.5 89.2
32.39 .55 3: 4:55. ! 65.8 224.2 -48.6 81.4
34.90 -8.49 3: 6: 9. ! 67.7 202.0 -55.1 71.2
35.49 -10.79 3: 6:27. ! 67.7 196.0 -56.6 68.2
36.07 -13.11 3: 6:46. ! 67.6 190.1 -58.0 64.9
36.62 -15.47 3: 7: 4. ! 67.2 184.2 -59.4 61.4
37.17 -17.85 3: 7:23. ! 66.7 178.4 -60.7 57.6
39.14 -27.75 3: 8:37. ! 63.2 157.5 -65.0 38.9
39.59 -30.34 3: 8:55. ! 62.0 152.9 -65.8 33.3
40.01 -32.98 3: 9:14. ! 60.7 148.5 -66.5 27.3
42.60 -67.66 3:12:37. ! 39.1 109.0 -59.2 314.4
42.54 -71.66 3:12:55. ! 36.3 105.6 -57.1 308.6
42.40 -75.93 3:13:14. ! 33.4 102.2 -54.7 302.9
42.15 -80.54 3:13:32. ! 30.1 98.6 -51.9 297.3
41.75 -85.61 3:13:51. ! 26.5 94.8 -48.7 291.7
41.16 -91.36 3:14: 9. ! 22.3 90.7 -44.8 285.9
40.24 -98.27 3:14:28. ! 17.1 86.0 -40.0 279.6
38.52 -108.14 3:14:46. ! 9.4 79.6 -32.6 271.6
Here is my prediction of the SAO 99095=PPM H 127364 occultation by (192)
Nausikaa on 1998 January 27th. I changed my orbit determination program
which can now handle both *apparent* CAMC and *astrometric* Hipparcos
observations simultaneously. I assume that the inclusion of the Hipparcos
(NDAC) positions will considerably improve the quality of the final orbits.
My combined CAMC/Hipparcos (NDAG) solution of the orbit of Nausikaa
was determined from observations covering a period of 5/1984 to 3/1994
with excellent mean residuals of 0.16" in RA and 0.14" and DE,
respectively. Unfortunately no more recent, high quality observations
are available to me. Nevertheless, I consider this orbit to be very
good. The position of the star was taken from the ACT catalogue. In
this case it agrees very well with the PPM H position (to within 0.05"
in RA and 0.02" in DE).
The occultation path computed from these data lies about 0.08" or 1.2
path width south of Goffin's nominal track shown on the Sky &
Telescope map (p. 86 of the 1998 February issue). The main reason for
the shift is a slightly different position of the asteroid determined
from my orbit compared to Goffin's orbit published in MPC 31001. There
is practically no difference in time between Goffin's and my
prediction. According to my update Nausikaa's shadow will now longer
cross Chicago, but Boston and Lake Erie will see an occultation.
Complete data for the central line are given in the table above.
- Martin Federspiel, Basel University, Switzerland
MIN. GEOCENTRIC Prediction comparison
U. T. SEP.
h m "
3 6.3 1.98N Nominal prediction, p. 86 of Feb. Sky and Telescope
3 6.4 1.89N Federspiel's update, other & USNO data to 1998 Jan. 9
_______________________________________________________________________
David Dunham, IOTA, 1997 Jan. 25, about noon EST