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Updated: 2018 AUG 12, 17:36 UT
Event Rank : 99
(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 2018 Sep 15 UT, the 53.7 km diameter asteroid (584) Semiramis will occult a 11.2 mag star in the constellation Perseus for observers along a path across north-western Australia from north of Perth across Western Australia and northern Northern Territory to Kununarra and Jabiru and across Papua - New Guinea from Okaba to Bogia.
In the case of an occultation, the combined light of the asteroid and the star will drop by 1.07 mag to 11.78 mag (the magnitude of the asteroid) for at most 5.4 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
113 13 2 -32 0 0 18 57 25 18 23 -43 113 39 58 112 46 10 113 52 20 112 33 54 0.72
114 6 54 -31 0 0 18 57 31 19 23 -43 114 33 44 113 40 10 114 46 4 113 27 57 0.72
115 1 10 -30 0 0 18 57 37 20 22 -43 115 27 55 114 34 31 115 40 11 114 22 21 0.72
115 55 51 -29 0 0 18 57 43 22 21 -43 116 22 32 115 29 17 116 34 47 115 17 8 0.72
116 51 2 -28 0 0 18 57 51 23 21 -42 117 17 40 116 24 30 117 29 55 116 12 23 0.73
117 46 46 -27 0 0 18 57 58 24 20 -42 118 13 23 117 20 16 118 25 37 117 8 9 0.73
118 43 7 -26 0 0 18 58 6 25 20 -42 119 9 44 118 16 36 119 21 58 118 4 30 0.73
119 40 8 -25 0 0 18 58 14 27 19 -41 120 6 47 119 13 37 120 19 2 119 1 30 0.73
120 37 55 -24 0 0 18 58 23 28 18 -40 121 4 37 120 11 20 121 16 53 119 59 12 0.74
121 36 30 -23 0 0 18 58 32 29 17 -40 122 3 17 121 9 52 122 15 36 120 57 42 0.74
122 36 0 -22 0 0 18 58 42 30 17 -39 123 2 53 122 9 16 123 15 15 121 57 3 0.74
123 36 30 -21 0 0 18 58 52 32 16 -39 124 3 31 123 9 37 124 15 56 122 57 22 0.74
124 38 3 -20 0 0 18 59 3 33 15 -38 125 5 15 124 11 2 125 17 45 123 58 42 0.74
125 40 48 -19 0 0 18 59 14 34 14 -37 126 8 11 125 13 35 126 20 47 125 1 10 0.75
126 44 50 -18 0 0 18 59 26 35 13 -36 127 12 27 126 17 23 127 25 9 126 4 52 0.75
127 50 16 -17 0 0 18 59 39 36 12 -35 128 18 10 127 22 33 128 31 0 127 9 56 0.75
128 57 14 -16 0 0 18 59 52 38 11 -34 129 25 27 128 29 14 129 38 26 128 16 28 0.75
130 5 54 -15 0 0 19 0 5 39 10 -33 130 34 28 129 37 32 130 47 38 129 24 37 0.75
131 16 24 -14 0 0 19 0 19 40 9 -32 131 45 24 130 47 38 131 58 45 130 34 32 0.76
132 28 57 -13 0 0 19 0 34 41 8 -31 132 58 25 131 59 43 133 12 0 131 46 25 0.76
133 43 44 -12 0 0 19 0 49 42 7 -30 134 13 45 133 13 59 134 27 35 133 0 26 0.76
135 1 0 -11 0 0 19 1 6 43 5 -29 135 31 38 134 30 39 135 45 47 134 16 51 0.76
136 21 2 -10 0 0 19 1 22 45 4 -27 136 52 24 135 50 0 137 6 52 135 35 53 0.76
137 44 10 - 9 0 0 19 1 40 46 2 -26 138 16 21 137 12 21 138 31 13 136 57 53 0.77
139 10 48 - 8 0 0 19 1 59 47 0 -24 139 43 56 138 38 4 139 59 15 138 23 12 0.77
140 41 23 - 7 0 0 19 2 18 48 358 -23 141 15 38 140 7 35 141 31 28 139 52 15 0.77
142 16 30 - 6 0 0 19 2 39 49 356 -21 142 52 3 141 41 27 143 8 31 141 25 34 0.77
143 56 52 - 5 0 0 19 3 1 49 354 -19 144 33 59 143 20 21 144 51 11 143 3 49 0.78
145 43 24 - 4 0 0 19 3 24 50 352 -17 146 22 24 145 5 7 146 40 31 144 47 49 0.78
147 37 19 - 3 0 0 19 3 49 51 349 -15 148 18 38 146 56 52 148 37 52 146 38 37 0.78
149 40 15 - 2 0 0 19 4 15 51 346 -13 150 24 30 148 57 6 150 45 10 148 37 40 0.78
Latitude Latitude Latitude Latitude
150 0 0 - 1 50 49 19 4 19 51 345 -13 - 2 11 17 - 1 30 28 - 2 20 41 - 1 21 11 0.79
151 0 0 - 1 23 41 19 4 32 52 344 -12 - 1 44 0 - 1 3 28 - 1 53 21 - 0 54 15 0.79
152 0 0 - 0 57 42 19 4 45 52 343 -11 - 1 17 53 - 0 37 37 - 1 27 10 - 0 28 27 0.79
153 0 0 - 0 32 50 19 4 58 52 341 -10 - 0 52 54 - 0 12 53 - 1 2 7 - 0 3 46 0.79
154 0 0 - 0 9 7 19 5 10 52 340 -8 - 0 29 3 0 10 44 - 0 38 13 0 19 47 0.79
155 0 0 0 13 30 19 5 23 52 338 -7 - 0 6 19 0 33 13 - 0 15 26 0 42 13 0.79
156 0 0 0 35 0 19 5 35 52 337 -6 0 15 18 0 54 37 0 6 14 1 3 34 0.79
157 0 0 0 55 25 19 5 48 51 335 -5 0 35 48 1 14 55 0 26 48 1 23 50 0.79
158 0 0 1 14 44 19 6 0 51 334 -4 0 55 13 1 34 9 0 46 16 1 43 0 0.79
Uncertainty in time = +/- 2 secs
Prediction of 2018 Aug 12.0
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