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Updated: 2017 JUL 16, 23:26 UT
Event Rank : 79
(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 2017 Sep 12 UT, the 68 km diameter asteroid (1796) Riga will occult a 8.4 mag star in the constellation Pisces for observers along a path across Australia, from Hervey Bay in morning twilight and a fairly low elevation, across southern Queensland, north-western New South Wales and south-eastern South Australia to Port Pirie, just west of Adelaide.
In the case of an occultation, the combined light of the asteroid and the star will drop by 6.60 mag to 15.00 mag (the magnitude of the asteroid) for at most 4.4 seconds.
This update is based on UNSO/Flagstaff astrometry for the asteroid kindly provided by Hugh Harris, astrometry for the asteroid kindly provided by Bill Owen, astrometry for the asteroid kindly provided by the IAU Minor Planet Center.
This work has made use of data from the European Space Agency (ESA) mission Gaia (http://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, http://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.
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.
Centre Star Star Sun Path Limits Error Limits Alt
E. Longitude Latitude U.T. Alt Az Alt Limit 1 Limit 2 Limit 3 Limit 4 Crn
o ' " o ' " h m s o o o o ' " o ' " o ' " o ' "
Longitude Longitude Longitude Longitude
133 33 11 -39 0 0 19 31 15 22 297 -20 132 23 50 134 45 9 131 10 12 136 7 45 2.46
134 15 1 -38 0 0 19 31 7 22 296 -20 133 5 11 135 27 35 131 51 7 136 51 0 2.46
135 0 26 -37 0 0 19 30 59 22 295 -19 133 49 53 136 13 50 132 35 12 137 38 23 2.46
135 49 35 -36 0 0 19 30 51 22 294 -19 134 38 7 137 4 6 133 22 35 138 30 10 2.46
136 42 46 -35 0 0 19 30 42 22 293 -18 135 30 6 137 58 43 134 13 27 139 26 41 2.46
137 40 16 -34 0 0 19 30 33 21 292 -18 136 26 5 138 58 2 135 8 2 140 28 28 2.46
138 42 31 -33 0 0 19 30 25 21 291 -17 137 26 25 140 2 35 136 6 37 141 36 7 2.47
139 50 4 -32 0 0 19 30 16 20 290 -16 138 31 35 141 13 1 137 9 35 142 50 31 2.47
141 3 37 -31 0 0 19 30 6 20 289 -15 139 42 8 142 30 15 138 17 25 144 12 54 2.48
142 24 11 -30 0 0 19 29 57 19 288 -14 140 58 53 143 55 33 139 30 45 145 45 3 2.48
143 53 6 -29 0 0 19 29 47 18 287 -13 142 22 52 145 30 49 140 50 24 147 29 45 2.49
145 32 27 -28 0 0 19 29 37 17 286 -12 143 55 37 147 18 54 142 17 31 149 31 44 2.51
147 25 23 -27 0 0 19 29 27 16 284 -10 145 39 21 149 24 49 143 53 42 152 0 24 2.54
149 37 34 -26 0 0 19 29 16 14 283 -8 147 37 41 151 58 31 145 41 24 155 20 57 2.58
Latitude Latitude Latitude Latitude
150 0 0 -25 50 51 19 29 15 14 283 -8 -24 58 52 -26 45 1 -24 3 54 -27 47 31 2.46
151 0 0 -25 27 48 19 29 10 13 282 -7 -24 36 30 -26 21 12 -23 42 12 -27 22 43 2.51
152 0 0 -25 6 46 19 29 6 12 282 -6 -24 16 4 -25 59 29 -23 22 22 -27 0 9 2.51
153 0 0 -24 47 43 19 29 3 11 281 -5 -23 57 33 -25 39 50 -23 4 22 -26 39 44 2.52
154 0 0 -24 30 35 19 28 59 11 281 -4 -23 40 53 -25 22 11 -22 48 10 -26 21 26 2.53
155 0 0 -24 15 21 19 28 56 10 280 -3 -23 26 4 -25 6 30 -22 33 44 -26 5 12 2.54
156 0 0 -24 2 0 19 28 53 9 280 -2 -23 13 2 -24 52 46 -22 21 3 -25 50 58 2.56
157 0 0 -23 50 28 19 28 51 8 279 -1 -23 1 48 -24 40 55 -22 10 6 -25 38 44 2.57
158 0 0 -23 40 46 19 28 48 7 279 0 -22 52 20 -24 30 57 -22 0 51 -25 28 26 2.59
159 0 0 -23 32 52 19 28 46 6 279 0 -22 44 36 -24 22 51 -21 53 19 -25 20 5 2.61
160 0 0 -23 26 45 19 28 44 5 278 1 -22 38 38 -24 16 36 -21 47 28 -25 13 39 2.64
161 0 0 -23 22 26 19 28 43 5 278 2 -22 34 23 -24 12 11 .. .. .. -25 9 7 2.68
162 0 0 -23 19 53 19 28 42 4 277 3 -22 31 52 -24 9 36 .. .. .. -25 6 30 2.74
163 0 0 -23 19 8 19 28 41 3 277 4 -22 31 6 -24 8 51 .. .. .. -25 5 47 2.84
164 0 0 -23 20 9 19 28 40 2 277 5 -22 32 3 -24 9 57 .. .. .. -25 6 58 3.04
Uncertainty in time = +/- 3 secs
Prediction of 2017 Jul 16.0
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