B/occ           Occultation lights curves                         (Herald+ 2025)
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Occultation light curves
    Dave Herald, Murrumbateman, Australia
    Dave Gault (Australia), Tsutomu Hayamizu (Japan), 
    Kazuhisa Miyashita (Japan), Hristo Pavlov (Australia), Steve Preston (USA),
    <Dave Herald (2025)>

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ADC_Keywords: Occultations

Abstract:
  We present the occultation light curves of both Lunar, and Asteroidal,
  occultations. Prior to about 2020, most light curves were recorded using
  video cameras. Subsequently an increasing number of light curves have
  been recorded using CMOS cameras. The vast majority of the light curves
  have been recorded using small aperture telescopes (40cm or less), and
  are unfiltered.

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], Tangra 
  [http://www.hristopavlov.net/Tangra3/], and PyOTE 
  [https://occultations.org/observing/software/pymovie/]. 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 organizations 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.
  
  Since around 2023, an increasing number of observations are being made using 
  12- or 16-bit CMOS cameras, with exposure durations being user-set without the
  limitations associated with video cameras. However, unlike video cameras,
  there will usually be very short intervals between exposures; occasionally
  such intervals can become significant if there are system delays in writing 
  images to an output device. 

  Lunar occultations
  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 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 analyze a lunar occultation light 
  curve are well determined - and are included in this archive.

  Asteroidal occultations
  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" at video
  frame rate time resolution. The angular resolution of Integrating video 
  cameras is reduced in proportion to the number of frames integrated. 
  CMOS cameras have an angular resolution that is entirely governed by the 
  exposure setting.

  The orientation of the occulting limb of an asteroid relative to the 
  star is generally not well established. The record does not attempt to 
  specify the orientation of the limb of the asteroid at the occultation event.
  Fresnel diffraction can have a effect that is apparent in the light curves.
  For small bodies (typically around 1km diameter or less) Fresnel diffraction
  can result in the light drop not being as deep as expected. None of the
  light curves are obtained using pass band filters.

File Summary:
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 FileName    Lrecl   Records    Explanations
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ReadMe          80        .  this file
moon.dat       228     6902  table description
asteroid.dat   188     6765  table description

LightCurves.txt .    .          Light curves

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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       [0.72/37802.36] Duration of recording
 33- 36   I4     ---    Np        [19/5064] Number of points
 38- 43   I6     ---    HIP        Hipparcos identifier
 45- 50   I6     ---    SAO        SAO identifier
 52- 57   I6     ---    XZ80Q      XZ80Q identifier
 59- 67   I9     ---    EPIC       Kepler2 EPIC identifier
 69- 79   A11    ---    TYC2       TYC2 identifier
 81- 84   I4     ---    UCAC2     ? UCAC2 identifier
 86- 95   A10    ---    UCAC4      UCAC4 identifier
 97-108   A12    "d:m:s" Lat        Latitude
110-122   A13    "d:m:s" Lon        Longitude
124-127   I4     m      Alt        Altitude of observer
129-153   A25    ---    ObsName    Observer name
155-161   F7.3   ---    AA         Moon axis angle
163-168   F6.3   ---    LibL      [-8.74/8.58] Moon Longitude libration
170-175   F6.3   ---    LibB      [-7.63/7.58] Moon Latitude libration
177-182   F6.2   ---    LimbSlope [-31.36/26.60] Moon Limb slope
184-189   F6.4   ---    Motion     Moon rate of motion normal to the lunar limb
191-197   F7.2   ---    CAMonn    [-179.98/179.98] Moon Contact angle
199-203   F5.3   ---    szMoon     Moon size
205-210   F6.2   ---    PaMoon     Moon position angle
212-215   A4     ---    CuspMoon  ? Moon Cusp angle
217-219   I3     ---    IllMoon    Moon illumination
221-222   I2     ---    AltMoon    Moon altitude
224-228   I5     ---    Seq       [1/13666] 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- 32   F9.2   s      Dur     [0.72/4573.20] Duration of recording
 34- 37   I4     ---    Np      [10/6137] Number of points
 39- 44   I6     ---    HIP      Hipparcos identifier
 46- 51   I6     ---    SAO      SAO identifier
 53- 53   I1     ---    XZ80Q    XZ80Q identifier
 55- 63   I9     ---    EPIC     Kepler2 EPIC identifier
 65- 75   A11    ---    TYC2     TYC2 identifier
 77- 80   I4     ---    UCAC2   ? UCAC2 identifier
 82- 91   A10    ---    UCAC4    UCAC4 identifier
 93-105   A13    "d:m:s" Lat      Latitude
107-119   A13    "d:m:s" Lon      Longitude
121-124   I4     m      Alt     [-81/2658] Altitude of observer
126-154   A29    ---    ObsName  Observer name
156-161   I6     ---    Num      Asteroid number
163-182   A20    ---    Name    ? Asteroid name
184-188   I5     ---    Seq     [101/13667] 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)

History:
  * 06-Jul-2016: new version
  * 29-Jul-2016: new version
  * 14-Dec-2016: new version
  * 14-Dec-2016: new version
  * 28-Feb-2017: new version
  * 03-Mar-2017: new version
  * 11-Jul-2017: new version
  * 22-Sep-2017: new version
  * 05-Feb-2018: new version
  * 29-Oct-2018: new version
  * 29-Oct-2018: new version
  * 26-Oct-2020: new version
  * 26-Oct-2020: new version
  * 17-Aug-2021: new version
  * 23-Sep-2021: new version
  * 23-Sep-2021: new version
  * 24-Aug-2022: new version
  * 09-Feb-2023: new version
  * 09-Feb-2023: new version
  * 09-Feb-2023: new version
  * 09-Mar-2023: new version
  * 10-Jun-2024: new version
  * 14-Jan-2025: new version

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(End)    Dave Herald, G. Landais [CDS]                               12-Jan-2025
