The following predicted occultations have been selected to illustrate the range of prediction outputs. [Because of this, there are far more information messages in this example than would usually occur!]
Occultation prediction for Kambah
E. Longitude 149 3 48.9, Latitude -35 23 49.3, Alt. 582m; Telescope dia 35cm; dMag 1.0
day Time P Star Sp Mag Mag % Elon Sun Moon CA PA VA AA Libration A B RV Cct R.A. (J2000) Dec
y m d h m s No D v r V ill Alt Alt Az o o o o L B m/o m/o "/sec o h m s o m s
07 Aug 22 5 42 44 d 2405SA2 6.6 s 62+ 104 21 50 92 49S 137 250 129 -3.9 +6.5 +0.5-2.6 .344 -28 16 44 17.4 -27 27 22
2405 is triple: 6.7 10.1 2.0" 15.3 : 6.6 14.0 21.4" 197.0
2405 = NSV 07935, 6.58, range 0.03 to ( 0.03V, Type E:
07 Aug 22 8 40 59 d 184665 G1 8.9 8.4 63+ 105 82 18 87N 92 256 85 -4.5 +6.6 +2.5-0.2 .312 9 16 49 8.1 -27 34 15
07 Aug 22 10 38 40 m 184699 F5 8.8 8.6 64+ 106 67 281 3S 182 68 175 -4.9 +6.6 +9.9+9.9 .000 -90 16 50 46.5 -27 54 7
Distance of 184699 to Terminator = 13.8"; to 3km sunlit peak = 0.0"
07 Aug 23 12 44 20 d X145167 M0 8.6 6.9V 73+ 118 53 269 67N 65 313 64 -5.9 +6.1 +1.1+1.9 .375 13 17 52 0.7 -28 1 21
X145167 = KW Sgr, 11.0 to 13.2P, Type SRC, Period 670. days
07 Aug 23 13 25 42 D 185893 A0 8.3 8.3 74+ 118 44 263 88N 86 333 85 -6.0 +6.1 +1.1+1.2 .409 -9 17 53 21.2 -28 3 26
07 Aug 23 14 23 18 d X145957 9.0 7.7v 74+ 119 33 257 83S 95 340 94 -6.1 +6.0 +0.8+1.0 .436 -18 17 55 13.2 -28 0 22
X145957 = V0776 Sgr, 10.6 to 11.1P, Type LB
07 Aug 25 6 38 25 m 2864dB8 4.6 4.6 88+ 140 11 28 102 8N 355 113 3 -5.0 +4.6 +9.9+9.9 .000 90 19 36 42.4 -24 53 1
R2864 = 52 Sagittarii
2864 is double: 4.7 9.2 2.6" 175.1
Distance of 2864 to Terminator = 6.9"; to 3km sunlit peak = 0.0"
07 Aug 25 6 39 4 Gr 2864dB8 4.6 4.6 88+ 140 11 28 ** GRAZE: CA 8.3N; Dist. 60km in az. 203deg. [Lat =-35.99-0.35(E.Long-149.06)]
Distance of 2864 to Terminator = 12.2"; to 3km sunlit peak = 1.9"
07 Aug 27 15 13 26 D 3177cA9 5.9 5.7 99+ 169 58 304 64N 41 265 58 -5.0 +1.2 +1.0+2.1 .429 12 21 43 4.4 -14 23 59
R3177 = 44 Capricorni
3177 is double: 6.8 6.8 0.10" 90.0
Distance of 3177 to Terminator = 13.8"; to 3km sunlit peak = 4.3"
07 Aug 28 9 30 55 R 165076 G5 9.6 9.0 33E 180 23 86 44S 216 340 236 -3.1 +0.1 +0.6+0.8 .459 -153 22 26 25.0 -10 0 0
07 Aug 28 10 2 46 D 146111 G0 7.7 7.4 0E 179 29 81 57U 109 234 129 -3.2 +0.1 +1.0-2.3 .333 -48 22 29 4.9 - 9 44 28
07 Aug 28 10 8 54 D 3301DK0 8.8 8.0 0E 179 30 80 49U 97 222 117 -3.2 +0.1 +1.0-1.6 .396 -36 22 29 18.6 - 9 39 46
3301 is double: 8.6 11.5 9.2" 291.4
07 Aug 29 13 22 10 Gr 146693 G5 7.5 7.1 98- 164 49 ** GRAZE: CA 10.9N; Dist. 12km in az. 143deg. [Lat =-35.53+0.61(E.Long-149.06)]
Distance of 146693 to Terminator = 2.1"; to 3km sunlit peak = 0.0"
08 Dec 29 10 6 52 D Jupiter -1.8 -1.8 3+ 20 -9 5 248 68S 101 335 111 -3.6 +0.7 -0.1+0.9 .446 -34 20 1 33.0 -20 55 10
Duration of planetary disk occultation: predicted time +/-33.1 secs
08 Dec 29 10 21 7 d Callisto 6.4 6.4 3+ 20 -11 3 246 62S 107 340 117 -3.6 +0.6 -0.2+0.7 .425 -39 20 2 2.1 -20 53 35
Duration of planetary disk occultation: predicted time +/-1.2 secs
10 Nov 29 23 41 49 r Juno 10.2 10.2 38- 76 58 38 301 36N 346 211 323 -0.9 +6.3 +0.5-2.3 .318 136 11 21 19.9 - 0 52 37
Duration of planetary disk occultation: predicted time +/-0.2 secs
Item Meaning
Day The day of the event. Occult searches for events on the basis of geocentric conjunctions that occur within a 24hr - with that period starting at the UT indicated in the date selection box. Users should ensure that the period starts near the middle of their day.
Time The predicted UTC, in hours, mins and secs.
P The Phase of the event. Values are:
D - disappearance
d - disappearance, but star is less than 1 mag brighter than the predicted visibility limit.
R - reappearance
r - reappearance, but star is less than 1 mag brighter than the predicted visibility limit.
Gr - grazing occultation at site. At mid-occultation, or closest approach, the star is less than 4" from the limb of the moon (either above or below).
gr - grazing occultation at site, but star is less than 1 mag brighter than the predicted visibility limit.
M - miss. At closest approach, the star is more than 4" above the limb of the moon
m - miss, but star is less than 1 mag brighter than the predicted visibility limit.
Star The star identifier. Three formats are used:
nnnn - A ZC star. When reporting occultations, the catalogue is identified with 'R'.
nnnnn, or
nnnnnn - An SAO star. When reporting occultations, the catalogue is identified with 'R'.
X nnnnnn - an XZ star. When reporting occultations, the catalogue is identified with 'X'.
D The double star code
Sp Star's spectral type. Only basic spectral type information is provided
Mag v The star's visual magnitude
Mag r The star's red magnitude. For observers using CCD video cameras, the red magnitude provides a better indication of visibility.
D The variable star code
% ill the percent illumination of the moon. If followed by a +, values are for a waxing moon; - for a waning moon; and E for illumination during a lunar eclipse.
Elon the elongation of the moon from the sun, in degrees. [Strictly, the quantity is calculated as the elongation of the star from the sun]
Sun Alt the altitude of the sun. The field is blank if the sun is lower than -12 deg. (Nautical twilight)
Moon Alt the altitude of the moon
Moon Az the azimuth of the moon
CA Cusp Angle - the angle of the event around the limb of the moon, measured from the nearest cusp. -'ve values indicate a bright limb event. The cusps are usually N (north) or S (south), but near full moon can be E (East) or W (west).
If a lunar eclipse is in progress, CA gives is the % distance from the centre of the umbra, and is followed by a 'U'. Values up to 103% are possible. Where an event occurs more than 103% of the umbral radius, the usual Cusp Angle value is displayed.
PA Position Angle - the angle of the event around the limb of the moon, measured from true north
VA Vertex Angle - the angle of the event around the limb of the moon measured anticlockwise from the vertex of the lunar limb - i.e. the point on the limb highest from the horizon
AA Axis Angle - the angle of the event around the limb of the moon, measured eastward from the moon's north pole. Essential for reappearance, as it locates the event with reference to lunar features. To use, mark a map of the moon around the circumference at 10 deg intervals, starting at the north pole. Mare Crisium is at about 300 deg.
[Note - the so-called Watts Angle differs from the Axis Angle by 0.21 deg. The term Watts Angle is limited to the context of accessing the Watts Charts. In all other situations, the term Axis Angle is preferred.]
Libration L the libration of the moon in longitude, as seen from the site at the time of the event
Libration B the libration of the moon in latitude, as seen from the site at the time of the event
A coefficient for correcting the prediction for changes in site location. The units are minutes of time per degree (or seconds of time per minute of arc). The correction to the prediction for a change in site, in seconds of time, is found by multiplying A by the change in site longitude (+'ve for changes towards the East) from the prediction site.
B same as for A, but for changes in latitude (+'ve to the north).
RV Radial Velocity - the radial rate of motion of the star relative to the lunar limb, in arcsecs per second.
Cct Contact Angle - the difference between the normal to the lunar limb and the direction of lunar motion. values range between -180 and +180. Disappearance have values in the range +90 to -90; reappearances are in the range 90 to 180, or -90 to -180. The sign of Cct indicates whether the star is to the north (+'ve) or south (-'ve) of the direction of motion.
RA The apparent RA of the star, calculated at an integral hour closest to the time of geocentric conjunction. Note : for planets and asteroids, the coordinates at the time of the occultation will differ from the values displayed here - but the prediction includes full allowance for the objects motion..]
Dec The apparent Declination of the star.- as for Right Ascension.
The following messages can appear
Item Meaning
Star name If the star is brighter than 5.0, and has a proper name, Bayer letter or Flamsteed number, this is given in a line like:
R2864 = 52 Sagittarii
Double star details If the star is a double star, the details are given in a line like:
2405 is triple: 6.7 10.1 2.0" 15.3 : 6.6 14.0 21.4" 197.0
The information provided for each pairing is the magnitude of each component, the separation and the PA, with pairings being separated by colons. Where an orbit is available for the pairing, the separation and PA are computed for the date of the occultation. Where there is no orbit, the separation and PA are estimated by linear extrapolation of the values in the double star catalogue.
Variable star details If the star is a variable star, the details are given in a line like:
X145167 = KW Sgr, 11.0 to 13.2P, Type SRC, Period 670. days
For regular variables with a known epoch, the phase in the current cycle is also provided.
Object diameter For planets, moons and asteroids, the prediction is for the center of the object. The prediction also includes a line like:
Duration of planetary disk occultation: predicted time +/-33.1 secs
To indicate the time difference from the start and end of the occultation of the object's disk. In this example, it will take 66 secs for the moon to cover the disk of the object.
Note: the displayed value assumes a circular object. No correction for the oblateness of Jupiter or Saturn is included.
Graze nearby Where an 'observable' grazing occultation occurs within the graze travel distance for the site, a separate prediction line appears - like:
07 Aug 29 13 22 10 Gr 146693 G5 7.5 7.1 98- 164 49 ** GRAZE: CA 10.9N; Dist. 12km in az. 143deg. [Lat =-35.53+0.61(E.Long-149.06)]
The first part of the line is the same as for any other prediction line. The additional information provided is:
Cusp angle at mid-graze
the distance from the site to the closest point on the graze path (in km)
the azimuth of the direction to the graze path
a simple formula to give the latitude of a point on the graze path for a specified longitude. In this example, you get the following latitudes by inserting the longitude into the formula
E. Longitude = +149.06 => latitude = -35.53
E. Longitude = +150.06 => latitude = -34.92
For observers in US/Canada, remember that your longitude is -'ve.
Terminator distance If a dark-limb occultation occurs less than 20" from the terminator, the distance to the terminator, and to a theoretical 3" high mountain beyond the terminator which could be sunlit, is given in a message like:
Distance of 2864 to Terminator = 12.2"; to 3km sunlit peak = 1.9"
The distance to the terminator is calculated on an assumption that the moon is perfectly smooth. The distance to a 3km sunlit peak indicates a 'worst-case' scenario of the effect of a high mountain (which could be on the near or far side of the moon).
To correct the event time for your location, use the A and B column.
Where #Lg = the base longitude, and #Lt = the base latitude,
and where Lg is your station longitude and Lt is your station latitude, the corrected time is:
for this table use #Lg=94.3450 and #Lt=39.0277
Where #Lg, Lg, #Lt, Lt are in decimal degrees.
You need also to pay attention to the value sign of the number.
If you are East or South of the base station, your time will be later than the base station.
If you are West or North of the base station, your time will be earlier than the base station.
The predictions also give special messages, in the following circumstances:
- if a dark-limb occultation occurs less than 20" from the
terminator, the distance to the terminator, and to a theoretical 3"
high mountain beyond the terminator which could be sunlit, is
given.
- if there is a grazing occultation of the star nearby. The message
gives the latitude of the graze path at the longitude of the
prediction site, the change of that latitude with a change in
longitude (positive to the East), and the cusp angle of the graze.
- if information is present for double stars; and
- for variable stars, the variable name, max and min magnitudes, type
of variable, and (if the elements are known) the phase in its
cycle. Note that for some variables, the minimum magnitude listed
is in fact the magnitude range - in such cases the 'minimum'
magnitude is shown as less than 0.5 mags., and in fact is the
magnitude variation.