Orwell Astronomical Society (Ipswich)
Summary of Lunar Occultations for 1999
During 1999, there are approximately 480 lunar occultations potentially observable from East Anglia, although many involve faint stars. There are no good grazing occultations of stars visible from the region, nor does the Moon occult any planets during the year.
This article summarises the circumstances of the best occultations during the year. It provides details for the location of Orwell Park Observatory; differences will in general be negligible for locations throughout East Anglia.
Table 1 lists occultation events during the year, of stars brighter than magnitude 4.0, where the circumstances are favourable. These events should be readily visible in small telescopes or binoculars.
The first two columns of the table list the date and time (UT) of the occultation. Column three specifies the phenomenon: "D" denotes a disappearance and "R" a reappearance. The table lists circumstances of D and/or R as dictated by the visibility of each phenomenon (determined by altitude, lunar phase, etc). Column four details the lunar phase (positive waxing and negative waning). Columns five and six give the altitude of the Sun and the star, both in degrees. (A negative solar altitude means that the Sun is below the horizon.) Columns seven and eight provide the star's magnitude and catalogue number.
| Date 1999 |
Time (UT) |
D R |
Lunar Phase |
Sun Alt (°) |
Star Alt (°) |
Mag | Star |
| 27 Jan | 00:57:13 01:53:58 | D R | 0.74+ | -55 -51 | 21 12 | 3.7 | γ Tau |
| 22 Mar | 18:29:31 19:38:40 | D R | 0.31+ | -4 -14 | 48 39 | 0.9 | Aldebaran |
| 18 Apr | 20:53:08 | D | 0.10+ | -16 | 9 | 3.7 | γ Tau |
| 24 Apr | 21:24:13 22:10:12 | D R | 0.71+ | -18 -21 | 46 41 | 1.4 | Regulus |
| 25 Jul | 20:57:23 21:57:33 | D R | 0.94+ | -8 -13 | 16 17 | 3.8 | μ Sgr |
| 26 Jul 27 Jul | 23:01:52 00:19:25 | D R | 0.98+ | -17 -19 | 17 14 | 2.9 | π Sgr |
| 13 Dec | 16:55:47 | D | 0.27+ | -10 | 21 | 2.8 | δ Cap |
Table 1. Occultations of stars brighter than magnitude 4.0.
The Moon’s orbit is defined by a range of periodicities, both short and long term. The short term periodicities mean that the Moon’s path through the sky follows a pattern whereby it almost repeats itself every month. The longer term periodicities gradually shift the orbit so that no particular pattern of approximate repetition can last more than a few years. This results in so called "occultation seasons", lasting for months or years, during which particular stars are repeatedly occulted, or repeatedly not occulted. The effect is most pronounced for the four first magnitude stars that the Moon can occult, namely Aldebaran, Spica, Antares and Regulus. We are currently leaving an occultation season of Aldebaran and entering one of Regulus. This is reflected by a single occultation of Aldebaran during the year (three during 1998) and by a single occultation of Regulus (none during 1998).
During the year, the Moon traverses some rich star fields. When this happens, a large number of occultations can occur during a single evening. Table 2 lists all evenings throughout the year when the Moon occults 15 or more stars; many are associated with the Moon’s passage through rich star fields in Taurus.
| Date, No occs | Date, No occs | Date, No occs | Date, No occs |
| 23 Jan, 20 | 20 Feb, 16 | 21 Feb, 16 | 21 Mar, 15 |
| 22 Mar, 20 | 23 Mar, 54 | 19 Apr, 27 | 20 Apr, 36 |
| 21 Apr, 37 | 17 May, 20 | 18 May, 17 | 19 May, 15 |
| 13 Nov, 15 | 14 Nov, 22 | 15 Nov, 17 | 15 Dec, 15 |
Table 2. Nights with 15 or more occultations.
James Appleton