Orwell Astronomical Society (Ipswich)

Home Events

Summary of Lunar Occultations for 2011

More about occultations.

Introduction

During 2011, there are over 700 lunar occultations potentially observable from East Anglia, although many involve faint stars. On 17 September, the track of a grazing occultation of a magnitude 5.8 star crosses the region. There are no good planetary occultations visible from the region during 2011.

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 6.0, 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
2011
Time
(UT)
D
R
Lunar
Phase
Sun
Alt (°)
Star
Alt (°)
Mag Star
14 Jan23:11:21D0.73+-58384.958 Ari, ζ Ari
15 Jan02:13:54D0.74+-50125.361 Ari, τ Ari
17 Jan20:33:44D0.95+-39564.21 Gem
17 Jan23:37:10D0.95+-58575.83 Gem, PU Gem
18 Jan02:14:03
03:07:37
D
R
0.96+-50
-43
37
29
3.37 Gem, η Gem
16 Feb01:35:09D0.92+-47364.981 Gem, g Gem
17 Feb20:02:33D1.00+-27295.16 Leo, h Leo
11 Mar
12 Mar
23:07:17
00:02:48
D
R
0.39+-40
-42
17
9
4.369 Tau, υ Tau
11 Mar
12 Mar
23:48:55
00:10:00
D
R
0.39+-41
-42
12
9
5.572 Tau
13 Mar21:14:52
22:14:31
D
R
0.59+-29
-36
49
41
3.37 Gem, η Gem
18 Mar19:17:37D0.99+-12205.955 Leo
18 Mar23:05:35D0.99+-37385.962 Leo, p3 Leo
07 Apr19:13:08
20:12:34
D
R
0.15+-6
-14
33
24
4.437 Tau, A1 Tau
07 Apr19:39:24
20:24:39
D
R
0.15+-10
-16
29
22
5.939 Tau, A2 Tau
15 Apr21:14:01D0.93+-19344.887 Leo, e Leo
11 May00:06:25D0.51+-2085.42 Leo, ω Leo
11 Aug20:50:07D0.96+-11165.957 Sgr
19 Sep
20 Sep
23:39:09
00:30:48
D0.55--37
-36
20
28
5.0109 Tau, n Tau
08 Oct19:54:57D0.90+-25315.063 Aqr, κ Aqr
09 Oct23:27:50D0.96+-44374.98 Psc, κ Psc
24 Oct05:19:58D0.10--12164.887 Leo, e Leo
30 Oct17:55:44D0.20+-1385.7ZC 2595
20 Nov02:06:59
02:46:54
D
R
0.33--47
-42
10
15
5.962 Leo, p3 Leo
03 Dec16:39:52D0.62+-8345.716 Psc
03 Dec23:52:08D0.64+-60124.919 Psc, TX Psc
07 Dec21:26:45D0.93+-50565.840 Ari
09 Dec19:09:56D0.99+-30355.7ZC 665
28 Dec16:51:55R0.17+-9255.146 Cap, c1 Cap

Table 1. Occultations of stars of magnitude 6.0 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. During 2011, the Moon occults eta Gem twice and 40 Ari once and grazes it once. There are no other repeated occultations of prominent stars during the year.

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 more than 10 stars. The very large numbers of occultations on 08 April and 07-08 May are associated with the passage of the Moon through star fields in Taurus and Gemini respectively.
 

Date, No occs Date, No occs Date, No occs Date, No occs
08 Jan, 11 09 Jan, 11 07 Feb, 18 08 Feb, 11
08 Mar, 13 09 Mar, 19 06 Apr, 12 07 Apr, 15
08 Apr, 46 09 Apr, 18 10 Apr, 23 06 May, 26
07 May, 45 08 May, 46 30 Oct, 15 28 Nov, 18
29 Nov, 20 27 Dec, 17 28 Dec, 20 29 Dec, 16

Table 2. Nights with more than 10 occultations.
 

Grazing Occultation

The track of one grazing occultation crosses East Anglia during the year. Table 3 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
2011
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
17 Sep 02:31 S 45 Profile 0.7 S Track Track 0.81- -23 56 175 5.8 40 Ari

Table 3. Grazing lunar occultation.
 


James Appleton