B/occ           Occultation lights curves                         (Herald+ 2016)
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Occultation light curves
    Dave Herald, Murrumbateman, Australia
    Derek Breit (USA), David Dunham (USA), Eric Frappa (France), 
    Dave Gault (Australia), Tony George (USA), Tsutomu Hayamizu (Japan), 
    Brian Loader (New Zealand), Jan Manek (Czech Rep.), 
    Kazuhisa Miyashita (Japan), Hristo Pavlov (Australia), Steve Preston (USA),
    Mitsuru Soma (Japan), John Talbot (New Zealand), Brad Timerson (USA)
    <Dave Herald (2016)>

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ADC_Keywords: Occultations

Description:
Lunar occultation light curves have been recorded since the mid-20th century 
using high-speed photomultipliers. Running at high cadence for high angular 
resolution, such recordings were usually made on large telescopes and limited to
the brighter stars - and were not large in number.

While a small number of video recordings of lunar and asteroidal occultations
were made from about 1980, they became common from about the year 2000, when 
inexpensive low-light security cameras became available. As of 2016, almost all 
lunar and asteroidal occultation observations are recorded using video, with the 
video recording being measured using software packages such as Limovie 
[http://astro-limovie.info/limovie/limovie_en.html], and Tangra 
[http://www.hristopavlov.net/Tangra3/]. As a result, light curves are now 
routinely generated for almost all lunar and asteroidal occultation 
observations, especially those coordinated through the International Occultation
Timing Association and related organisations around the world. This is resulting 
in large numbers of occultation light curves being obtained each year - albeit 
with some limitations on time resolution and signal-to-noise ratios.

As of 2016, video recordings are mainly made using one or other of the two 
international video standards - NTSC, or PAL. Both NTSC and PAL use an 
interlaced video scan, whereby each frame of the video is comprised of two 
interlaced, time-sequential, fields. The frame rate of an NTSC system is 29.97 
frames/sec (59.94 fields/sec), while that for PAL is 25 frames/sec (
50 fields/sec). Consistent with broadcast television standards, the majority of
video cameras used for recording occultations use 8-bit CCD's. However some 
video recordings are made using progressive scan, 12 to 16-bit digital video
systems.

For lunar occultations, the temporal resolution is governed by a combination of 
the frame (or field) rate of the video recording, and the rate of motion of the 
moon. The typical topocentric motion of the moon is between about 0.3"/sec and 
0.4"/sec. The motion of the lunar limb in a direction normal to the star is 
reduced by the cosine of the difference between the direction of motion of the 
moon and the position angle of the star. As a result, the typical rate of motion 
of the lunar limb normal to the star is in the range 0.2 to 0.4 "/sec. At video 
frame rates this provides a spatial resolution of about 0.01" to 0.02" at frame 
rate, or 0.005" to 0.01" at field rate. 

In recent years it has been possible to accurately determine the orientation of
the lunar limb at the point of an occultation, using data from the Japanese 
Kaguya satellite, and more recently the US Lunar Reconnaissance Orbiter - Lunar 
Orbiter Laser Altimeter (LRO-LOLA). The LRO-LOLA data allows the slope of the 
lunar limb to be reliably determined over circumferential distances of less than 
0.2" in the sky plane.  As a result, all data elements required to analyse a 
lunar occultation light curve are well determined - and are included in this 
archive.

The motion of most asteroids is much less than the moon. As a result, the 
angular resolution attainable at video frame rate is much smaller than for a 
lunar occultation, and is commonly in the range 0.0001" to 0.001". However 
asteroidal occultations frequently involve fainter objects than for lunar 
occultations, and many observers use integrating video cameras to detect 
these fainter occultations; the resolution attainable with an integrating 
camera is reduced in proportion to the number of frames integrated.

Unlike lunar occultations, the orientation of the occulting limb of an 
asteroid relative to the star is generally not well established. 
Furthermore it can generally be assumed that the limb of an asteroid is likely
to have significant irregularities at scales greater than the potential 
angular resolution attainable, but smaller than the angular distance between
adjacent observed occultation chords. There is also the issue of the rotational
orientation of the asteroid differing for observers located at different points 
along the occultation path, placing a limit on the accuracy of the limb slope 
that can be derived from adjacent occultation chords. Accordingly, at this time 
the record does not attempt to specify the orientation of the limb of the 
asteroid at the occultation event.

File Summary:
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 FileName    Lrecl   Records    Explanations
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ReadMe          80        .  this file
moon.dat       231     6659  table description
asteroid.dat   184      686  table description

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Byte-by-byte Description of file: moon.dat
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 Bytes Format Units  Label     Explanations
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  1- 22   A22    "datime" Date      Observation date
 24- 31   F8.2   s      Dur       [0.0/37802.4]? Duration of recording
 33- 36   I4     ---    Np        [19.0/4044.0]? Number of points
 38- 43   I6     ---    HIP       [0.0/118298.0]? Hipparcos identifier
 45- 50   I6     ---    SAO       [0.0/190295.0]? SAO identifier
 52- 57   I6     ---    XZ80Q     [0.0/243644.0]? XZ80Q identifier
 59- 67   I9     ---    EPIC      Kepler2 EPIC identifier
 69- 79   A11    ---    TYC2      TYC2 identifier
 81- 88   I8     ---    UCAC2     UCAC2 identifier
 90- 99   A10    ---    UCAC4     UCAC4 identifier
101-112   A12    "d:m:s" Lat       Latitude
114-126   A13    "d:m:s" Lon       Longitude
128-131   I4     m      Alt       [0.0/2035.0]? Altitude of observer
133-157   A25    ---    ObsName   Observer name
159-165   F7.3   ---    AA        [0.1/357.0]? Moon axis angle
167-172   F6.3   ---    LibL      ? Moon Longitude libration
174-179   F6.3   ---    LibB      ? Moon Latitude libration
181-186   F6.2   ---    LimbSlope ? Moon Limb slope
188-193   F6.4   ---    Motion    ? Moon rate of motion normal to the
                                lunar limb
195-201   F7.2   ---    CAMonn    [-180.0/180.0]? Moon Contact angle
203-207   F5.3   ---    szMoon    [0.9/1.1]? Moon size
209-214   F6.2   ---    PaMoon    [0.0/360.]? Moon position angle
216-219   A4     ---    CuspMoon  Moon Cusp angle
221-223   I3     ---    IllMoon   [4.0/100.0]? Moon illumination
225-226   I2     ---    AltMoon   [5.0/82.0]? Moon altitude
228-231   I4     ---    Seq       [1.0/7338.0]? Sequential number of the light
                                curves (CDS)

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Byte-by-byte Description of file: asteroid.dat
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 Bytes Format Units  Label     Explanations
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  1- 22   A22    "datime" Date    Observation date
 24- 30   F7.2   s      Dur     [-44.3/422.4]? Duration of recording
 32- 35   I4     ---    Np      [10.0/5999.0]? Number of points
 37- 42   I6     ---    HIP     [0.0/116660.0]? Hipparcos identifier
 44- 49   I6     ---    SAO     [0.0/211579.0]? SAO identifier
 51- 51   I1     ---    XZ80Q   [0.0]? XZ80Q identifier
 53- 61   I9     ---    EPIC    Kepler2 EPIC identifier
 63- 73   A11    ---    TYC2    TYC2 identifier
 75- 82   I8     ---    UCAC2   UCAC2 identifier
 84- 94   A11    ---    UCAC4   UCAC4 identifier
 96-108   A13    "d:m:s" Lat     Latitude
110-122   A13    "d:m:s" Lon     Longitude
124-127   I4     m      Alt     [0.0/2438.0]? Altitude of observer
129-155   A27    ---    ObsName Observer name
157-162   I6     ---    Num     [-1.0/523692.0]? Asteroid number
164-179   A16    ---    Name    Asteroid name
181-184   I4     ---    Seq     [78.0/7345.0]? Sequential number of the light
                              curves (CDS)

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See also:
    VI/122 : The Marginal Zone of the Moon - Watts' Charts (Watts, 1963)
    VI/132 : Lunar Occultation Archive (Herald+ 2012)
    B/astorb : Orbits of Minor Planets (Bowell+ 2014)

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(End)    Dave Herald, G. Landais [CDS]                               29-aug-2016
