Orwell Astronomical Society (Ipswich)

Home Events

Summary of Lunar Occultations for 2008

More about occultations.

Introduction

During 2008, there are approximately 660 lunar occultations potentially observable from East Anglia, although many involve faint stars. During the year, the Moon occults the Pleiades three times, although in all cases under unfavourable circumstances. Also during the year, two grazing occultations and two planetary occultations are visible from the region.

There are two lunar eclipses during 2008, with details as follows:

When the Moon is in umbral eclipse the glare which it produces is markedly reduced, enabling observation of occultations of much fainter stars than would normally be possible.

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.

Occultations of Bright Stars

Table 1 lists occultation events during the year, of stars down to magnitude 5.0, 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
2008
Time
(UT)
D
R
Lunar
Phase
Sun
Alt (°)
Star
Alt (°)
Mag Star
17 Feb23:54:37D0.88+-50525.057 Gem, A Gem
29 Feb04:43:39
05:52:51
D
R
0.49--19
-8
8
10
2.823 Sco, τ Sco
14 Mar18:50:58R0.54+-9654.6136 Tau
20 Apr03:23:36D1.00+-1265.575 Vir
12 May20:13:38R0.57+-5444.431 Leo, A Leo
13 May22:55:35
23:35:41
D
R
0.68+-18
-19
25
20
4.858 Leo, d Leo
17 Jul01:11:28D0.98+-1563.227 Sgr, φ Sgr
17 Jul23:44:41D1.00+-17134.652 Sgr, h2 Sgr
20 Sep02:26:26
03:19:4
D
R
0.73--27
-21
59
62
3.920 Tau, Maia
22 Oct04:53:18D0.42--16513.947 Cnc, δ Cnc, DL Cnc
13 Nov18:26:23
19:06:58
D
R
0.99--21
-28
22
28
3.717 Tau, Electra
13 Nov19:14:15
20:11:21
D
R
0.99--29
-37
29
37
2.825 Tau, η Tau, Alcyone
13 Nov19:55:53
20:41:31
D
R
0.99--35
-42
35
42
3.627 Tau, Atlas
06 Dec21:46:06
22:31:27
D
R
0.60+-53
-57
26
20
4.518 Psc, λ Psc
11 Dec19:32:38D0.99+-34445.459 Tau, χ Tau
13 Dec21:08:21
22:11:21
D
R
0.98--48
-56
38
47
3.127 Gem, ε Gem, Mebsuta

Table 1. Occultations of stars of magnitude 5.0 or brighter.
 

Occultation Seasons

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 Moon can occult four first magnitude stars, namely Aldebaran, Spica, Antares and Regulus. During recent years, there has been only one occultation season of a first magnitude star, namely Regulus during 2007. In 2008, conversely, no occultations of first magnitude stars are visible from East Anglia.

A season of occultations of the Pleiades visible from East Anglia began in 2007; during the year the Moon occulted the star cluster on four occasions. In 2008, the Moon will occult the Pleiades three times; however, none of the opportunities presents a favourable observing opportunity. Brief details are as follows:

The occultation season of the Pleiades continues through to 2009.

Nights With Many Occultation Events

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 12 or more stars. The large numbers of occultations on the evenings of 08-13 April are associated with the passage of the Moon in front of the rich star fields of Taurus and Cancer. On 08 April, the Moon passes within 2° of the Pleiades. Its apparent motion eastwards then carries it into the Milky Way, close to the galactic equator in Taurus on 10 April and in front of the Beehive Cluster (M44) in Cancer on 13 April. On 08-09 May the Moon passes through the rich star fields of the Milky Way into western Gemini.
 

Date, No occs Date, No occs Date, No occs Date, No occs
11 Jan, 12 13 Jan, 19 10 Feb, 14 21 Feb, 13
11 Mar, 27 12 Mar, 15 14 Mar, 17 08 Apr, 14
10 Apr, 83 11 Apr, 25 13 Apr, 13 08 May, 45
09 May, 46 02 Dec, 14 - -

Table 2. Nights with 12 or more occultations.
 

Occultations of Planets

Both Venus and Mars are occulted during 2008. Table 3 provides details for Venus; timings refer to the centre of the planetary disk. The interpretation of the columns in the table is the same as that of table 1 (with the obvious difference that the data refers to a planet rather than a star). The occultation of Mars takes place shortly after midday on 10 May and will be very difficult to observe.
 

Date
2008
Time
(UT)
D
R
Lunar
Phase
Sun
Alt (°)
Planet
Alt (°)
Mag
01 Dec15:49:02
17:18:07
D
R
0.13+-1
-13
13
8
-4.1

Table 3. Occultation of Venus.


In addition, there is a close approach of the Moon to Neptune: the Moon will appear within one tenth of a lunar radius of the planet on 06 November. However, the lunar phase will be 56% and Neptune will be shining at magnitude 7.9, difficult to discern due to lunar glare.

Grazing Occultations

The tracks of two grazing occultations cross East Anglia during the year; unusually, the events occur on consecutive evenings! Table 4 summarises the circumstances.

The tracks of three grazing occultations cross East Anglia during the year. Table 4 summarises the circumstances. Columns one and two give the date and time of the graze and column three specifies the lunar limb involved. Column four indicates the distance between Orwell Park Observatory and point X on the track, on land, where the distance between the two is least; column five links to a plot of the lunar limb profile visible from X. Column six specifies a north or south displacement of the observer's position, relative to the track, based upon inspection of the limb profile, to maximise the chances of witnessing multiple disappearance and reappearance events. Column seven links to an on-line Google Earth plot of the track and column eight links to an off-line image of it. (The plot and image illustrate the nominal track, with no displacement applied.) Column nine details the lunar phase (positive for waxing, negative for waning) and column 10 the altitude of the Sun (a negative solar altitude means that the Sun is below the horizon). Columns 11 and 12 provide the horizontal co-ordinates of the star (azimuth in the order N→E→S→W). Columns 13 and 14 specify the star and its magnitude.
 

Date
2008
Time
(UT)
Limb Dist
OPO
(km)
Limb
Profile
Track
Shift
(km)
Google
Earth
Track
Google
Earth
Image
Lunar
Phase
Sun
Alt
(°)
Star
Alt
(°)
Star
Azi
(°)
Mag Star
12 Mar 18:25 S 15 Profile 0 Track Track 0.31+ -6 54 233 6.4 22 Tau, Asterope
13 Mar 23:07 N 53 Profile 0 Track Track 0.44+ -39 24 284 6.9 ZC 746

Table 4. Grazing lunar occultations.
 

NB: 22 Tau is the fainter component of the double star Asterope, the most northerly member of the Pleiades visible to the naked eye.


James Appleton