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Summary of Lunar Occultations for 2012

More about occultations.

Introduction

During 2012, there are almost 600 lunar occultations potentially observable from East Anglia, although many involve faint stars. On 01 April, the track of a grazing occultation of a magnitude 5.9 star crosses the region, passing less than 8 km from Orwell Park. Just two and a half months later, the track of a grazing occultation of Jupiter and the Galilean satellites crosses North Norfolk.

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 5.5, 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
2012
Time
(UT)
D
R
Lunar
Phase
Sun
Alt (°)
Star
Alt (°)
Mag Star
06 Jan01:26:28D0.89+-56345.356 Tau, V724 Tau
05 Mar23:25:17D0.92+-43464.365 Cnc, α Cnc
06 Mar04:18:44D0.93+-2165.276 Cnc, κ Cnc
02 Apr23:33:38D0.81+-32345.42 Leo, ω Leo
25 Apr20:32:53
20:47:50
D
R
0.17+-12
-13
23
21
3.0123 Tau, ζ Tau
29 Apr22:52:18D0.55+-22235.276 Cnc, κ Cnc
13 May02:38:44D0.48--11135.146 Cap, c1 Cap
26 Sep21:32:23D0.89+-32295.146 Cap, c1 Cap
07 Oct01:41:35
02:48:27
D
R
0.61--38
-30
41
50
4.662 Ori, χ2 Ori
11 Oct02:38:35
03:34:58
D
R
0.23--32
-25
12
21
5.42 Leo, ω Leo
07 Nov01:22:23
02:20:19
D
R
0.49--49
-42
21
30
5.276 Cnc, κ Cnc
16 Nov17:13:50R0.11+-1183.813 Sgr, μ Sgr
17 Nov17:05:58
18:06:29
D
R
0.20+-10
-19
16
11
4.943 Sgr, d Sgr
26 Dec18:23:13D0.98+-22325.3106 Tau, l Tau
27 Dec21:24:00D1.00+-49494.662 Ori, χ2 Ori

Table 1. Occultations of stars of magnitude 5.5 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 effect can be seen in table 1, with each of 76 Cnc, 2 Leo, 46 Cap and χ2 Ori occulted at least twice.

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 25 and 26 April are associated with the passage of the Moon through star fields of the Milky Way in Taurus.
 

Date, No occs Date, No occs Date, No occs Date, No occs
28 Jan, 21 24 Feb, 11 25 Feb, 11 26 Feb, 13
26 Mar, 12 27 Mar, 11 29 Mar, 23 25 Apr, 37
26 Apr, 45 16 Nov, 11 17 Nov, 42 15 Dec, 11
16 Dec, 21 17 Dec, 20 18 Dec, 12 -

Table 2. Nights with more than 10 occultations.
 

Occultation of Jupiter

There has been a dearth of good occultations of planets visible from East Anglia in recent years. The last occultations of a planet observed by members of OASI were of Saturn, on 02 March 2007 and 22 May 2007. In the early hours of the morning of 15 July 2012, there will be a lunar occultation of Jupiter. From Orwell Park, event times (referring to the centre of the planetary disc) will be as follows: disappearance 01:57:14 UT; reappearance 02:09:54 UT. Unfortunately, circumstances are not ideal as the altitude of Jupiter will be only 10°. From North Norfolk, the event will be manifest as a graze (details below). The next good occultation of a planet visible from East Anglia after the Jupiter event will not be until 2022, when both Mars and Uranus are occulted. (There is an earlier but observationally very difficult occultation of Saturn on 25 October 2014.)

Grazing Occultations

Grazing occultations of 29 Cnc, Jupiter and its Galilean satellites cross 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
2012
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 Object
01 Apr 19:29 N 7.9 Profile 1.5 S Track Track 0.70+ -10 52 175 5.9 29 Cnc
15 Jul 02:05 N 91 Profile 1.5 S Track Track 0.16- -14 10 69 - Jupiter & Galileans

Table 3. Grazing lunar occultations.
 

The graze track of 29 Cnc passes only 7.9 km from Orwell Park and, as the event occurs in the early evening, it offers a very convenient observing opportunity. From Orwell Park, the event will be manifest as an occultation of very short duration. Grazes of Jupiter are rare and the event of 15 July, even though its circumstances are far from ideal (early morning event shortly before dawn, low altitude, northern limb event), will generate much interest. The graze track of Jupiter is approximately 68 km wide and this offers the prospect of finding a location in Norfolk from which to observe a graze of either Io or Europa followed a few minutes later by a graze of Jupiter.


James Appleton