Occultations and Transits Special Interest Group

revised 2005 Feb 21

Total Occultations by the Moon

The Moon may look big, but it actually covers a small region of sky. So at any given time, there are usually few, if any, "bright" stars behind the Moon’s disk. Fortunately, the Moon is relatively close to the Earth, astronomically speaking. As it circles the Earth at 2000 mph, it appears to move relatively fast through the starry sky, providing the potential to cover a star every now and then. If you are watching as the Moon approaches, the star will suddenly disappear on one side of the Moon and reappear just as suddenly a while later: a total occultation.

A Total Occultation

The rapid disappearance or reappearance was an early argument that the Moon had no atmosphere; otherwise, the star would dim as it approached the Moon's limb. In some circumstances, the arrangement of the occultation allows faint companions to be seen for a split second while the brighter primary is covered. The classic example is the companion to Antares. The 7th magnitude companion can be challenging to see next to the 1st magnitude primary, but it is easy to see during favorable occultation reappearances.

Total occultations are generally visible from a large area of the Earth. Essentially, the star is casting a shadow of the Moon. So, the region of visibility is as large as the Moon itself.

The Best Total Occultations for the year 2005

The list below is the best and/or brightest lunar occultations for the year 2005. These events can be seen from anywhere in the Pittsburgh area, with some allowance for slightly different times depending on your location. Some of these will be visible in binoculars. All of them will be visible in a small telescope (2 to 4 inch aperture). For a searchable database of some 1400 occultations, please turn to the AAAP Occultation Planner page.

   Star      Date      Time (UT) Event  mag    %  cusp   PA Star Star  Sun
             mm/dd/yy   h  m  s              SNL angle    °  Alt   Az  Alt

19 lambda Cnc  2/5/04   3:50:11    D    5.9   98   42S  172   70  143  -58
86    Vir     2/28/05  11:35:58    R    5.8  -82   87N  294   22  229   -4
20 sigma Sco   3/3/05   7:20:50    R    2.9  -55   42N  328    7  133  -48
21 alpha Sco   3/3/05  10:58:47    D    0.9  -53  -82N   91   23  179  -10
61 tau Ari    3/15/05   2:39:14    D    5.2   25   24N    8   19  282  -36
63 tau2 Ari   3/15/05   3:08:06    D    5.2   25   21S  143   14  286  -40
SAO 76945     3/17/05   0:42:59    D    7.7   43   41S  134   62  250  -15
SAO 77818     3/18/05   0:53:53    D    7.0   52   70N   71   70  238  -17
SAO 79726     3/20/05   2:13:36    D    6.8   71   48N   60   72  223  -31
SAO 80310     3/21/05   0:18:32    D    6.8   79   47N   65   62  119  -10
SAO 76740     4/13/05   1:43:01    D    7.5   19   63S  106   27  282  -20
49    Aur     4/15/05   1:04:51    D    5.0   35   88N   90   54  263  -13
SAO 78580     4/15/05   3:07:16    D    7.4   36   85S   98   32  281  -31
SAO 80165     4/17/05   3:39:03    D    7.3   55   50S  145   42  267  -34
SAO 98944     4/19/05   5:50:35    D    6.3   74   50N   73   30  265  -38
53    Leo     4/20/05   4:41:10    D    5.3   82   46S  160   46  237  -37
13    Vir     4/22/05   3:07:34    D    5.9   94   86S  121   48  169  -29
47    Gem     5/13/05   2:14:42    D    5.6   21    5S  179   27  284  -18
SAO 79170     5/13/05   2:31:59    D    6.4   21   46N   50   24  286  -20
SAO 79241     5/13/05   4:20:43    D    6.4   22   64S  120    5  301  -30
SAO 80496     5/15/05   1:29:53    D    7.6   38   67N   83   50  256  -11
SAO 80529     5/15/05   3:14:21    D    7.0   38   65N   81   31  273  -24
SAO 119150    5/19/05   2:28:09    D    7.0   76   52N   76   49  202  -18
21 alpha Sco  5/24/05   8:14:24    D    0.9  -99  -12N   65   14  215  -16
21 alpha Sco  5/24/05   9:14:05    R    0.9  -99   81S  311    7  226   -8
SAO 98597     6/12/05   1:35:24    D    7.6   23   69S  127   33  268   -8
37    Leo     6/13/05   4:23:09    D    5.7   32   24S  175    6  283  -25
SAO 183900    6/20/05   3:49:42    D    5.4   94   88N   93   25  188  -23
SAO 183982    6/20/05   6:27:39    D    5.4   95   83N   86   12  222  -24
33    Cap     6/25/05   5:51:02    R    5.5  -86   79N  268   18  141  -26
63 tau2 Ari    7/2/05   7:47:53    R    5.2  -16   82N  266   11   72  -18
65    Ari      7/2/05   8:31:44    R    5.9  -16   72S  240   19   78  -13
60    Sgr     7/21/05   8:26:45    D    5.0  -99   55S   38   11  221  -16
29    Aqr     7/23/05   8:17:23    R    6.4  -94   58S  226   31  197  -18
24    Psc     7/25/05   9:49:26    R    6.1  -78   87S  245   45  198   -4
36    Tau     7/30/05   8:55:17    R    5.7  -28   76N  274   38   90  -14
SAO 77619      8/1/05   7:58:36    R    7.1  -13   57S  242   12   64  -22
136   Tau      8/1/05   8:13:01    D    4.5  -13  -86S   98   14   66  -20
136   Tau      8/1/05   9:08:14    R    4.5  -13   53S  238   24   73  -12
SAO 78710      8/2/05   8:07:57    R    6.8   -7   47N  326    5   58  -21
gamma1 Sgr    8/16/05   0:42:31    D    4.3   80   12S  164   18  165   -5
SAO 92763     8/24/05   7:52:28    R    6.3  -73   35S  194   58  142  -28
40    Ari     8/25/05   4:53:35    R    6.0  -65   78N  264   23   85  -38
SAO 76215     8/26/05   8:54:03    R    5.5  -53   86N  261   60  116  -19
SAO 76244     8/26/05   9:47:17    R    6.1  -52   57N  291   69  137  -10
SAO 77295     8/28/05   7:43:39    R    6.5  -34   71S  251   31   79  -30
SAO 78480     8/29/05   8:43:32    R    7.5  -25   47S  233   32   79  -22
SAO 78483     8/29/05   8:49:01    R    7.6  -25   72N  294   34   80  -21
SAO 78496     8/29/05   9:10:49    R    7.8  -25   79S  265   38   83  -17
49    Aur     8/29/05  10:00:30    R    5.0  -24   80S  266   47   90   -9
SAO 80089     8/31/05   9:10:30    R    7.0  -10   47S  247   17   73  -18
19 lambda Cnc 8/31/05   9:33:45    R    5.9  -10    2S  201   21   76  -14
SAO 184547    9/11/05   1:05:27    D    6.5   45   51S  137   14  213  -17
29    Aqr     9/16/05   4:39:43    D    6.4   94   61S   91   31  196  -46
61 tau Ari    9/22/05   4:40:19    R    5.2  -79   53S  216   37   93  -49
59 chi Tau    9/23/05   8:33:42    R    5.4  -69   90N  259   71  136  -29
SAO 77121     9/24/05   9:43:14    R    6.3  -59   56N  299   75  141  -17
SAO 79170     9/26/05   9:30:45    R    6.4  -40    7S  195   55   99  -20
2  omega1 Cnc 9/27/05   7:23:45    R    5.9  -31   80S  273   21   74  -41
SAO 80496     9/28/05   8:59:32    R    7.6  -22   70N  309   28   84  -26
SAO 80529     9/28/05  10:51:03    R    7.0  -22   69S  268   48  103   -5
SAO 186867   10/10/05   0:09:29    D    6.8   41   60N   58   17  202  -16
SAO 188257   10/11/05   0:00:30    D    7.0   53   73S   98   21  186  -15
SAO 189509   10/12/05   2:11:58    D    6.7   65   71N   54   22  204  -39
epsilon Cap  10/13/05   2:13:55    D    4.5   75   88N   67   29  192  -40
43 kappa Cap 10/13/05   5:40:49    D    4.8   77   18S  140    8  237  -56
44    Psc    10/16/05   7:47:10    D    6.0   98   50N   26   27  247  -42
SAO 92763    10/18/05   3:32:31    R    6.3  -99   36S  183   52  126  -53
SAO 76215    10/20/05   2:16:17    R    5.5  -92   44N  298   27   81  -42
SAO 76350    10/20/05   7:29:44    R    6.4  -90   37N  306   74  187  -46
SAO 76880    10/21/05  10:47:57    R    6.8  -82   66N  284   57  258  -10
SAO 77625    10/22/05   6:18:46    R    5.6  -76   29S  205   53   96  -56
SAO 78710    10/23/05   5:11:38    R    6.8  -67   13S  195   31   78  -61
SAO 79726    10/24/05  11:19:23    R    6.8  -56   34N  335   75  199   -5
SAO 80809    10/26/05   7:43:11    R    6.7  -38   35N  344   27   87  -45
SAO 189151    11/8/05   0:33:56    D    7.0   38   53N   41   18  209  -28
SAO 190252    11/9/05   1:47:48    D    7.1   50   70S   92   21  215  -42
SAO 164948   11/10/05   1:27:42    D    7.0   61   19N  357   32  200  -38
SAO 77295    11/18/05  11:13:26    R    6.5  -93   40S  209   38  276  -11
SAO 78440    11/19/05   9:45:00    R    6.8  -88   64N  293   65  250  -27
SAO 80089    11/21/05   9:29:51    R    7.0  -73   55S  245   74  174  -31
19 lambda Cnc11/21/05  10:30:05    R    5.9  -73   51S  242   70  218  -19
77 sigma Leo 11/25/05   7:20:01    R    4.1  -37   50S  253   15   95  -55
60    Sgr     12/4/05  22:39:00    D    5.0   14   44N   37   16  211   -9
20    Psc     12/9/05   3:54:03    D    5.6   59    8N  344   21  247  -66
19    Ari    12/12/05   0:23:04    D    6.0   86   39N   22   56  130  -28
SAO 75755    12/13/05   2:35:16    D    6.7   93   61N   51   70  162  -53
58 zeta  Ari 12/13/05   6:13:14    D    5.0   94   49S  122   46  258  -69
136   Tau    12/15/05  23:40:55    D    4.5 -100    6S  132   19   69  -20
136   Tau    12/16/05   0:16:04    R    4.5 -100   78S  205   25   74  -26
4     Cnc    12/18/05  10:32:03    R    6.2  -92   46N  318   50  262  -23
37    Leo    12/21/05   3:48:49    R    5.7  -74   73S  272   11   81  -65
5  beta Vir  12/23/05   8:09:33    D    3.8  -55  -57S  146   35  123  -50
5  beat Vir  12/23/05   9:26:13    R    3.8  -54   89S  292   46  144  -36

where

Star: Is the "name" of the star. One of the following is given (in order of precedence) : the Flamsteed and/or Bayer designation and constellation abbreviation; the Smithsonian Astrophysical Observatory catalog number (numbers starting with SAO); or the USNO catalog number (numbers starting with XZ), or
Date & Time are in Universal Time (UT, Greenwich England), accurate to a few seconds for Wagman Observatory. Otherwise, watch continuously for a few minutes, depending on the distance from Wagman. Subtract 5 hours from Universal Time (UT) to get Eastern Standard Time (E.S.T.); subtract 4 hours to get Eastern Daylight Time (E.D.T.). The time is expressed in 24-hour military time. Thus, 13:00 is 1 p.m., 14:00 is 2 p.m., and so on. After subtracting the 4 or 5 hours to get Eastern time, a negative time indicates the event occurs on the previous date (add 24 to the negative number in this case to get the appropriate time on the previous date).
Event is the event, either D for disappearance behind Moon (generally along the left side: the celestial east side), or R for reappearance (along the right side: the celestial west side). Refer to the CA (cusp angle) to determine if the event is a bright limb or a dark limb event.
mag is the visual magnitude (brightness) of the star being occulted. The larger the number, the fainter the star and the more difficult it is to see the star at the Moon's limb or in the glare of its light.
% SNL: Percentage of Moon sunlit; that is, the Moon's phase, either waxing (+) or waning (-). 0% is a New Moon, +50% First Quarter, 100% Full Moon, -50% Third Quarter.
Cusp angle is the angle in degrees measured from the Moon's northern (N) or southern cusp (S) to the position of the occultation. The positive (+) events occur on dark limb (or in the umbra during an eclipse) and are easiest to see; negative (-) events occur on bright limb. See the figure below.
PA is the position angle measured in degrees. Similar to the position angle for double stars, it is the angle from due north (0°) to the point on the Moon's limb where the Event occurs. 90° is celestial east (to the left), 180° is celestial south, 270° is celestial west (to the right). See the figure below.
Star Alt is the altitude (in degrees) or angle of the star above (+) or below (-) the horizon at the time of the event. (Hopefully, the star is above the horizon. Otherwise, you are wasting your time!) 0° indicates the star is on the horizon, 45° is halfway up, and 90° is straight overhead.
Star Az is the azimuth (in degrees) or angle of the star measured around horizon from due north. 90° is east, 180° is south, 270° is west, etc.
Sun Alt is the altitude (in degrees) of sun below (-) or above (+) the horizon. Events that occur with the Sun above the horizon are daytime events.

Cusp Angle and Position Angle

Other Total Occultation Links:

IOTA Welcome Page	Home page of the International Occultation Timing Association, a non-profit organization devoted to the scientific study of occultations.
IOTA's Lunar Occultations	Extensive information for total and grazing occultations.
John Holtz's Occultation Calculations	My web page with links to download total occultation calculations for the current year as either a text file or comma separated file (.CSV).
Sky & Telescope's Occultation page	Sky & Telescope's page with background information and details on some of the best upcoming occultations.

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