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Updated: 2011 Aug 23, 02:18 UT
Event Rank : 93
(The event Rank is a measure of the likelihood of observing an event, and is equal to the probability of at least one successful observation by a team of two observers spaced 1/8 path width just inside opposite sides of the predicted path. An event rank of 100 indicates that the prediction is expected to be very accurate).
THE UPDATED PATH
Note: The duration given in the line below is the interval during which the occultation shadow sweeps across the Earth - please see the minute markers on the map to determine the approximate time for your location.
On 2011 Oct 04 UT, the 80 km diameter asteroid (925) Alphonsina will occult a 12.1 mag star in the constellation Pegasus for observers along a path across New South Wales, western Victoria and extreme south-eastern South Australia.
In the case of an occultation, the combined light of the asteroid and the star will drop by 1.2 mag to 12.8 mag (the magnitude of the asteroid) for at most 7.7 seconds.
This update is based on UNSO/Flagstaff astrometry for the asteroid kindly provided by Alice Monet, historical astrometry from the MPC files (via AstDys), and the following catalogs for the star position: UCAC.
Additional details of this and other events are available at Steve Preston's website at http://www.asteroidoccultation.com/
EVENT DETAILS SUMMARY :Important Note regarding Accuracy:
The uncertainty interval in path widths given above (and shown as a 1-sigma uncertainty ellipse on the plot) refers to RMS deviation and is applied as a +/- range. In other words, a path uncertainty of 1.0 path widths means that the actual center of the asteroid's shadow path should fall within plus or minus 1 path width of the plotted path center. However path errors larger than 1 sigma have been observed so observers should be alert for primary occultations within plus or minus 3 sigma of the updated path.
Further, almost all asteroidal satellites discovered so far have been found within 10 diameters of the asteroid (since this distance is deep enough within the gravitational well to be stable over long timescales). Therefore, if monitoring for secondary events, observing out to about 10 path-widths either side of the predicted track remains worthwhile.
We therefore recommend that you monitor for events if your observing location is up to +/- 10 path-widths from the predicted track. If not monitoring for occultations by secondary bodies you should observe from locations within 3 sigma of the nominal path.
In terms of time, the predictions are now usually accurate to about +/- 0.3 minute so you should be most attentive during the predicted minute of the event. However if intending to catch a potential satellite occultation you should start observing at least 10 times the predicted central duration before the predicted closest approach time for your location, and continue for a similar period afterwards.
Occultation of TYC 1686-01582-1 by 925 Alphonsina on 2011 Oct 4
Centre Star Star Sun Path Limits Error Limits
E. Longitude Latitude U.T. Alt Az Alt Limit 1 Limit 2 Limit 3 Limit 4
o ' " o ' " h m s o o o o ' " o ' " o ' " o ' "
Longitude Longitude Longitude Longitude
136 49 22 -41 0 0 13 33 55 30 341 -42 135 35 7 138 5 12 134 26 40 139 18 3
138 8 54 -40 0 0 13 33 41 30 339 -43 136 54 5 139 25 24 135 45 10 140 38 59
139 31 8 -39 0 0 13 33 27 31 338 -45 138 15 34 140 48 29 137 6 3 142 3 1
140 56 19 -38 0 0 13 33 12 31 336 -46 139 39 49 142 14 46 138 29 31 143 30 27
142 24 47 -37 0 0 13 32 57 32 334 -47 141 7 6 143 44 33 139 55 51 145 1 40
143 56 52 -36 0 0 13 32 40 32 333 -49 142 37 46 145 18 16 141 25 19 146 37 8
145 33 2 -35 0 0 13 32 24 32 331 -50 144 12 12 146 56 25 142 58 18 148 17 24
147 13 49 -34 0 0 13 32 6 33 329 -51 145 50 52 148 39 37 144 35 13 150 3 12
148 59 52 -33 0 0 13 31 48 33 327 -52 147 34 21 150 28 38 146 16 35 151 55 27
150 52 4 -32 0 0 13 31 28 33 325 -54 149 23 23 152 24 30 148 3 2 153 55 20
152 51 31 -31 0 0 13 31 8 33 322 -55 151 18 55 154 28 33 149 55 23 156 4 32
154 59 44 -30 0 0 13 30 46 32 320 -56 153 22 11 156 42 41 151 54 41 158 25 24
155 0 0 -29 59 53 13 30 46 32 320 -56 -29 15 19 -30 45 29 -28 34 19 -31 29 22
Uncertainty in time = +/- 4 secs
Prediction of 2011 Aug 23.0
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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