by Byron Soulsby
Theodore Lunar Observatory, Australia
Getting Started
Your location
To observe occultations of stars by the Moon you need firstly to find your location. The easiest way to do this now is to download and install Google Earth. Once installed you can follow the instructions to locate approximately your position on the surface of the Earth. Google will allow you to zoom in until you have accurately located your site. The beauty of Google Earth is that your Latitude, Longitude and height above sea level is also given with your location.
Occultation Predictions
The best software for computing lunar occultations as been written by David Herald, Australia and is made available for download from IOTA. Once installed, it can be run to produce a list of occultation predictions for your site for any period of time, up to twelve months ahead is the most convenient time.
There are a number of options available including the listing of grazing occultations that might be visible from your site or within a short distance from you.
Observing Occultations
I suggest you commence your observing of stellar occultations to get the hang of all the procedures before venturing into graze observations. One previous difficult aspect was having available a reliable and convenient time base, which is necessary to obtain value from your observations. A recent innovation is to download a reliable synchronizing clock to regularly update the time on your computer. This is Dimension 4.
Reporting Observations
The clearing house for lunar occultations has been managed for some time now in Japan by ILOC.
This organization allocates a site identifier to you for future reference and regularly publishes world wide results for all occultations which are then applied to improve the orbit of the Moon. There is also considerable guidance concerning all aspects of occultations available here.
Methods
Location
I
have included several examples to give you an idea of the software
mentioned in the above introduction, starting with Google
Earth. Here is
a screen shot of my location in Australia where my open observatory is
situated.
The image shows
my block and house with the location given at the bottom from the
pointerwhich was placed on the
image before capturing. These coordinates should be used for the
prediction of all occultations with the program Occult.
Predictions
This software can be downloaded from IOTA.
Once this is installed, select the Occultation Predictions program and include your location, then select the dates required for predictions (here 13 to 20 May) as shown below:
y m d h m s No D V ill Alt Alt Az o o o o L B m/o m/o "/sec o h m s o m s
07 05 13 18 46 36 r 109304 K0 9.2 13- 42 14 71 32S 192 321 214 -2.4 -3.2 +0.0+1.8 .394 -135 24 36 16.3 6 24 7
07 05 13 19 54 55 r X 56009 10.2 12- 41 -12 27 59 25S 185 320 207 -2.5 -3.4 -0.1+2.2 .343 -132 24 38 24.5 6 44 59
07 05 14 19 31 2 R 92476 G0 9.2 6- 27 9 67 76S 242 11 262 -0.7 -4.7 +0.3-0.2 .579 +176 1 31 25.0 13 28 48
07 05 14 20 1 38 R 92490 MA 9.3 6- 27 -10 14 62 83N 263 36 284 -0.6 -4.8 +0.8-0.9 .497 +153 1 32 17.3 13 44 24
07 05 19 8 10 25 D 78042 K7 7.9v 9+ 34 7 313 36S 137 0 137 +5.5 -6.9 +0.2-0.2 .401 -34 6 9 59.8 28 40 0
78042 = V0450 Aur, 7.94 to 8.10 Hp, Type SRB:
Graze of 78039 K0 nearby at Lat = -35.78 -0.65(E.Long -149.06), CA = 20.5N
19 8 21 36 Gr 78039 K0 8.9 9+ 34 5 311
Closest distance to graze path is 33km at azimuth 219
07 05 19 8 21 51 m 78039 K0 8.9 9+ 34 5 311 21N 14 238 13 +5.4 -6.9 +0.8+0.5 .471 -7 6 9 52.2 29 6 31
07 05 20 7 46 38 d 79155 G0 9.5 16+ 47 -9 19 327 79N 82 292 76 +6.4 -6.2 +1.9+1.1 .365 +30 7 12 40.3 27 25 35
07 05 20 8 9 46 D X 99111S 7.2 16+ 47 17 323 67S 115 329 109 +6.3 -6.2 +1.1+0.3 .436 -3 7 13 16.0 27 12 53
X 99111 is triple : 7.3 7.2 1.06" 130.5 : 7.2 12.3 15.6" 94.0
07 05 20 8 9 47 D 1093SF8 6.6s 16+ 47 17 323 67S 115 329 109 +6.3 -6.2 +1.1+0.3 .436 -3 7 13 16.0 27 12 53
1093 is triple : 7.2 7.3 1.06" 310.5 : 6.4 12.3 14.1" 88.0
1093 = NSV 03453, 6.43 to 6.46 V , Type
07 05 20 8 15 49 d 79165 A2 9.2 16+ 47 16 321 35S 148 3 142 +6.3 -6.1 +0.3-0.7 .356 -36 7 13 0.1 27 5 10
07 05 20 8 36 33 d X 99277 10.0 16+ 47 13 318 69N 71 289 65 +6.3 -6.1 +1.8+1.7 .343 +41 7 14 8.8 27 20 22
07 05 20 9 20 51 d 79201 K0 9.1 16+ 48 7 310 43S 140 4 133 +6.2 -6.0 +0.1-0.3 .430 -28 7 15 14.5 26 55 18
07 05 20 8 9 49 d X 99111S 7.2 16+ 47 17 323 67S 115 329 109 +6.3 -6.2 +1.1+0.3 .435 -4 7 13 16.0 27 12 53
X 99111 is triple : 7.3 7.2 1.06" 130.5 : 7.2 12.3 15.6" 94.0
07 05 20 8 9 50 D 1093SF8 6.6s 16+ 47 17 323 67S 115 329 109 +6.3 -6.2 +1.1+0.3 .435 -4 7 13 16.0 27 12 53
1093 is triple : 7.2 7.3 1.06" 310.5 : 6.4 12.3 14.1" 88.0
1093 = NSV 03453, 6.43 to 6.46 V , Type
The time of the event is in Universal Time (UT) so allow for this when converting to your local time. There is NO ALLOWANCE for summer time. As an example, the last entry shows an occultation at 07y 05m 20d 8h 9m 50s of a triple star, 1093SF8 disappearing behind the Moon. The magnitude of these stars are 7.2, 7.3 at 1.06" separation and at position angle 310.5 degrees and the third star is magnitude 6.4.
Because my telescope is only 90mm aperture, the cut off limiting magnitude is around 7.5.
The software gives an option to locate the star to be observed by a mouse over the star and using ctrl+click to give a diagram as shown below:
Predictions
This software can be downloaded from IOTA.
Once this is installed, select the Occultation Predictions program and include your location, then select the dates required for predictions (here 13 to 20 May) as shown below:
Occultation
Predictions for Theodore in May 2007
E.Long.
149 7 1.9 Lat. -35 27
4.1 Alt. 679m. T.dia
90mm. dMag 0.0
day Time P
Star Sp Mag % Elon
Sun Moon CA
PA VA WA Libration
A B RV
Cct
R.A.
Decy m d h m s No D V ill Alt Alt Az o o o o L B m/o m/o "/sec o h m s o m s
07 05 13 18 46 36 r 109304 K0 9.2 13- 42 14 71 32S 192 321 214 -2.4 -3.2 +0.0+1.8 .394 -135 24 36 16.3 6 24 7
07 05 13 19 54 55 r X 56009 10.2 12- 41 -12 27 59 25S 185 320 207 -2.5 -3.4 -0.1+2.2 .343 -132 24 38 24.5 6 44 59
07 05 14 19 31 2 R 92476 G0 9.2 6- 27 9 67 76S 242 11 262 -0.7 -4.7 +0.3-0.2 .579 +176 1 31 25.0 13 28 48
07 05 14 20 1 38 R 92490 MA 9.3 6- 27 -10 14 62 83N 263 36 284 -0.6 -4.8 +0.8-0.9 .497 +153 1 32 17.3 13 44 24
07 05 19 8 10 25 D 78042 K7 7.9v 9+ 34 7 313 36S 137 0 137 +5.5 -6.9 +0.2-0.2 .401 -34 6 9 59.8 28 40 0
78042 = V0450 Aur, 7.94 to 8.10 Hp, Type SRB:
Graze of 78039 K0 nearby at Lat = -35.78 -0.65(E.Long -149.06), CA = 20.5N
19 8 21 36 Gr 78039 K0 8.9 9+ 34 5 311
Closest distance to graze path is 33km at azimuth 219
07 05 19 8 21 51 m 78039 K0 8.9 9+ 34 5 311 21N 14 238 13 +5.4 -6.9 +0.8+0.5 .471 -7 6 9 52.2 29 6 31
07 05 20 7 46 38 d 79155 G0 9.5 16+ 47 -9 19 327 79N 82 292 76 +6.4 -6.2 +1.9+1.1 .365 +30 7 12 40.3 27 25 35
07 05 20 8 9 46 D X 99111S 7.2 16+ 47 17 323 67S 115 329 109 +6.3 -6.2 +1.1+0.3 .436 -3 7 13 16.0 27 12 53
X 99111 is triple : 7.3 7.2 1.06" 130.5 : 7.2 12.3 15.6" 94.0
07 05 20 8 9 47 D 1093SF8 6.6s 16+ 47 17 323 67S 115 329 109 +6.3 -6.2 +1.1+0.3 .436 -3 7 13 16.0 27 12 53
1093 is triple : 7.2 7.3 1.06" 310.5 : 6.4 12.3 14.1" 88.0
1093 = NSV 03453, 6.43 to 6.46 V , Type
07 05 20 8 15 49 d 79165 A2 9.2 16+ 47 16 321 35S 148 3 142 +6.3 -6.1 +0.3-0.7 .356 -36 7 13 0.1 27 5 10
07 05 20 8 36 33 d X 99277 10.0 16+ 47 13 318 69N 71 289 65 +6.3 -6.1 +1.8+1.7 .343 +41 7 14 8.8 27 20 22
07 05 20 9 20 51 d 79201 K0 9.1 16+ 48 7 310 43S 140 4 133 +6.2 -6.0 +0.1-0.3 .430 -28 7 15 14.5 26 55 18
07 05 20 8 9 49 d X 99111S 7.2 16+ 47 17 323 67S 115 329 109 +6.3 -6.2 +1.1+0.3 .435 -4 7 13 16.0 27 12 53
X 99111 is triple : 7.3 7.2 1.06" 130.5 : 7.2 12.3 15.6" 94.0
07 05 20 8 9 50 D 1093SF8 6.6s 16+ 47 17 323 67S 115 329 109 +6.3 -6.2 +1.1+0.3 .435 -4 7 13 16.0 27 12 53
1093 is triple : 7.2 7.3 1.06" 310.5 : 6.4 12.3 14.1" 88.0
1093 = NSV 03453, 6.43 to 6.46 V , Type
The time of the event is in Universal Time (UT) so allow for this when converting to your local time. There is NO ALLOWANCE for summer time. As an example, the last entry shows an occultation at 07y 05m 20d 8h 9m 50s of a triple star, 1093SF8 disappearing behind the Moon. The magnitude of these stars are 7.2, 7.3 at 1.06" separation and at position angle 310.5 degrees and the third star is magnitude 6.4.
Because my telescope is only 90mm aperture, the cut off limiting magnitude is around 7.5.
The software gives an option to locate the star to be observed by a mouse over the star and using ctrl+click to give a diagram as shown below:
As you can see
the example star(s)
contact the lunar limb at a position between the craters Grimaldi and
Lagrange, there is an option to show this as a reversed image if the
view in your telescope is flipped.
Observing
Set up your telescope to acquire and carefully track the Moon some time before the occultation is due to occur. When the star becomes visible in the field of view it should be tracked rather than the Moon, to ensure accurate timing of the occultation. Follow the star into the dark Moon which probably can not be seen, but near the predicted time the star will either dim in brightness (if a multiple star) and disappear, or just simply disappear instantly from view. Record the star catalogue number and the time of disappearance for forwarding later to ILOC.
Reporting
Your timing of occultations are best collected over a period of time of say at least two months as individual reporting of events consumes postage costs. ILOC prefers that reporting be made on their standard form and this should be obtained from their web site.
Grazing Occultations
The Occult program also lists grazing occultations near your site. These occultations when observed, give critical data to improve knowledge of the Moon's edge or limb. When a star just clips the edge of the Moon it will disappear behind mountains then re-appear in the valleys. To observe these grazes you will need to be exactly at the correct location which places you near the Moon's limb as cast onto the Earth's surface. A number of observers gives the most useful data from these events as the profile of the Moon can be assessed from observers equally spaced across the profile of the event.
Final Comments
Occultations can be observed visually through your telescope or with an imaging device where an instant result can be obtained. When observed visually, allowance for your reaction time must be included. Read more about this and other matters in the ILOC pages.
Observing
Set up your telescope to acquire and carefully track the Moon some time before the occultation is due to occur. When the star becomes visible in the field of view it should be tracked rather than the Moon, to ensure accurate timing of the occultation. Follow the star into the dark Moon which probably can not be seen, but near the predicted time the star will either dim in brightness (if a multiple star) and disappear, or just simply disappear instantly from view. Record the star catalogue number and the time of disappearance for forwarding later to ILOC.
Reporting
Your timing of occultations are best collected over a period of time of say at least two months as individual reporting of events consumes postage costs. ILOC prefers that reporting be made on their standard form and this should be obtained from their web site.
Grazing Occultations
The Occult program also lists grazing occultations near your site. These occultations when observed, give critical data to improve knowledge of the Moon's edge or limb. When a star just clips the edge of the Moon it will disappear behind mountains then re-appear in the valleys. To observe these grazes you will need to be exactly at the correct location which places you near the Moon's limb as cast onto the Earth's surface. A number of observers gives the most useful data from these events as the profile of the Moon can be assessed from observers equally spaced across the profile of the event.
Final Comments
Occultations can be observed visually through your telescope or with an imaging device where an instant result can be obtained. When observed visually, allowance for your reaction time must be included. Read more about this and other matters in the ILOC pages.
Produced by the Theodore Lunar Observatory Australia, 2007 May 15.