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Summary of Lunar Occultations for 2013

More about occultations.

Introduction

During 2013, there are almost 600 lunar occultations potentially observable from East Anglia, although many involve faint stars. On 06 March, the track of a grazing occultation of a magnitude 3.8 star crosses the region, passing 50 km from Orwell Park. No lunar occultations of planets occur in 2013 visible from East Anglia (the next is of Saturn, on 25 October 2014).

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
2013
Time
(UT)
D
R
Lunar
Phase
Sun
Alt (°)
Star
Alt (°)
Mag Star
04 Mar02:33:52
03:14:25
D
R
0.59--35
-30
9
13
3.99 Sco, ω1 Sco
21 May20:51:07D0.85+-8284.840 Vir, ψ Vir
24 May22:00:24D1.00+-13155.045 Lib, λ Lib
11 Sep20:01:41D0.40+-1674.54 Oph, ψ Oph
13 Oct23:07:16D0.72+-46124.513 Aqr, ν Aqr
22 Nov00:23:37
01:18:39
D
R
0.83--57
-53
42
48
3.654 Gem, λ Gem
11 Dec22:17:04D0.73+-56354.371 Psc, ε Psc
16 Dec16:25:29D0.99+-664.9104 Tau, m Tau
17 Dec06:30:17D1.00+-1284.3119 Tau, CE Tau

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. In recent years, occultation seasons have been evident, with repeated occultations of bright stars being forecast for Orwell Park; this is not the case in 2013.

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 large numbers of occultations on 15 April and 07 November are associated with star fields in Taurus and Sagittarius respectively.
 

Date, No occs Date, No occs Date, No occs Date, No occs
14 Jan, 11 18 Jan, 11 15 Mar, 14 16 Mar, 21
14 Apr, 15 15 Apr, 50 16 Apr, 12 13 May, 14
14 May, 18 15 May, 20 10 Oct, 13 11 Oct, 12
07 Nov, 42 05 Dec, 15 06 Dec, 26 -

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
2013
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
06 Mar 05:35 S 50 Profile 1.2 N Track Track 0.35- -9 14 157 3.8 13 Sgr, μ Sgr

Table 3. Grazing lunar occultation.
 


James Appleton