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Updated: 2013 JAN 26, 17:05 UT
Event Rank : 39
(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 2013 Feb 20 UT, the 113 km diameter asteroid (909) Ulla will occult a 10.4 mag star in the constellation Virgo for observers along a path near Tasmania, South Australia and north Western Australia, close to Hobart, Melbourne, Adelaide and Derby.
In the case of an occultation, the combined light of the asteroid and the star will drop by 4.3 mag to 14.7 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.
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
144 39 20 -50 0 0 14 41 55 25 29 -29 145 54 30 143 23 0 150 1 3 138 55 7
144 27 45 -49 0 0 14 42 1 26 29 -30 145 41 35 143 12 47 149 43 50 138 49 51
144 14 36 -48 0 0 14 42 6 27 30 -31 145 27 12 143 0 55 149 25 27 138 42 32
143 59 57 -47 0 0 14 42 12 28 30 -32 145 11 24 142 47 26 149 5 57 138 33 16
143 43 52 -46 0 0 14 42 17 28 31 -33 144 54 15 142 32 26 148 45 21 138 22 8
143 26 23 -45 0 0 14 42 23 29 31 -34 144 35 48 142 15 57 148 23 41 138 9 13
143 7 34 -44 0 0 14 42 29 30 32 -35 144 16 5 141 58 4 148 1 0 137 54 35
142 47 27 -43 0 0 14 42 35 31 33 -36 143 55 7 141 38 47 147 37 19 137 38 17
142 26 3 -42 0 0 14 42 42 31 33 -37 143 32 57 141 18 10 147 12 38 137 20 24
142 3 24 -41 0 0 14 42 48 32 34 -38 143 9 37 140 56 14 146 46 59 137 0 56
141 39 32 -40 0 0 14 42 55 33 35 -39 142 45 6 140 33 0 146 20 21 136 39 56
141 14 28 -39 0 0 14 43 1 33 36 -40 142 19 27 140 8 30 145 52 46 136 17 26
140 48 11 -38 0 0 14 43 8 34 36 -41 141 52 39 139 42 44 145 24 14 135 53 27
140 20 43 -37 0 0 14 43 16 35 37 -42 141 24 44 139 15 44 144 54 44 135 27 59
139 52 3 -36 0 0 14 43 23 35 38 -43 140 55 40 138 47 29 144 24 17 135 1 4
139 22 13 -35 0 0 14 43 30 36 39 -44 140 25 28 138 17 59 143 52 52 134 32 41
138 51 10 -34 0 0 14 43 38 36 40 -45 139 54 8 137 47 13 143 20 29 134 2 50
138 18 55 -33 0 0 14 43 45 37 41 -46 139 21 38 137 15 12 142 47 7 133 31 31
137 45 27 -32 0 0 14 43 53 37 42 -47 138 47 59 136 41 54 142 12 45 132 58 42
137 10 44 -31 0 0 14 44 1 38 43 -48 138 13 8 136 7 19 141 37 22 132 24 22
136 34 46 -30 0 0 14 44 9 38 44 -49 137 37 5 135 31 24 141 0 56 131 48 29
135 57 30 -29 0 0 14 44 18 38 45 -50 136 59 48 134 54 8 140 23 27 131 11 2
135 18 54 -28 0 0 14 44 26 39 46 -51 136 21 15 134 15 29 139 44 52 130 31 57
134 38 57 -27 0 0 14 44 35 39 48 -52 135 41 24 133 35 24 139 5 10 129 51 12
133 57 35 -26 0 0 14 44 43 39 49 -53 135 0 11 132 53 51 138 24 18 129 8 43
133 14 46 -25 0 0 14 44 52 39 50 -53 134 17 35 132 10 46 137 42 14 128 24 25
132 30 25 -24 0 0 14 45 1 39 51 -54 133 33 32 131 26 5 136 58 56 127 38 14
131 44 30 -23 0 0 14 45 10 40 53 -55 132 47 58 130 39 45 136 14 19 126 50 4
130 56 54 -22 0 0 14 45 20 40 54 -56 132 0 50 129 51 40 135 28 21 125 59 48
130 7 34 -21 0 0 14 45 29 40 55 -56 131 12 1 129 1 44 134 40 58 125 7 19
129 16 23 -20 0 0 14 45 38 40 56 -57 130 21 27 128 9 52 133 52 5 124 12 28
128 23 14 -19 0 0 14 45 48 39 58 -57 129 29 2 127 15 55 133 1 38 123 15 4
127 28 1 -18 0 0 14 45 58 39 59 -58 128 34 39 126 19 46 132 9 31 122 14 55
126 30 34 -17 0 0 14 46 8 39 60 -58 127 38 9 125 21 16 131 15 39 121 11 48
125 30 43 -16 0 0 14 46 18 39 62 -59 126 39 24 124 20 11 130 19 54 120 5 24
124 28 16 -15 0 0 14 46 28 38 63 -59 125 38 12 123 16 21 129 22 8 118 55 23
123 23 0 -14 0 0 14 46 39 38 64 -59 124 34 23 122 9 28 128 22 13 117 41 20
122 14 39 -13 0 0 14 46 49 37 66 -59 123 27 41 120 59 16 127 20 0 116 22 44
121 2 53 -12 0 0 14 47 0 37 67 -59 122 17 49 119 45 21 126 15 15 114 58 55
119 47 19 -11 0 0 14 47 11 36 68 -59 121 4 28 118 27 16 125 7 45 113 29 3
Uncertainty in time = +/- 16 secs
Prediction of 2013 Jan 27.0
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