B/occ Occultation lights curves (Herald+ 2016)
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)
=2016yCat....102033H 2016yCat....102033H
<Dave Herald (2016)>
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:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . this file
moon.dat 226 6902 table description
asteroid.dat 187 6765 table description
LightCurves.txt . . Light curves
--------------------------------------------------------------------------------
Byte-by-byte Description of file: moon.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 22 A22 "datime" Date Observation date
24- 29 F6.2 s Dur [0.72/108.84] Duration of recording
31- 34 I4 --- Np [19/5064] Number of points
36- 41 I6 --- HIP Hipparcos identifier
43- 48 I6 --- SAO SAO identifier
50- 55 I6 --- XZ80Q [3/243644] XZ80Q identifier
57- 65 I9 --- EPIC Kepler2 EPIC identifier
67- 77 A11 --- TYC2 TYC2 identifier
79- 82 I4 --- UCAC2 ? UCAC2 identifier
84- 93 A10 --- UCAC4 UCAC4 identifier
95-106 A12 "d:m:s" Lat Latitude
108-120 A13 "d:m:s" Lon Longitude
122-125 I4 m Alt Altitude of observer
127-151 A25 --- ObsName Observer name
153-159 F7.3 --- AA [0.11/356.98] Moon axis angle
161-166 F6.3 --- LibL [-8.74/8.58] Moon Longitude libration
168-173 F6.3 --- LibB [-7.63/7.58] Moon Latitude libration
175-180 F6.2 --- LimbSlope [-31.36/26.6] Moon Limb slope
182-187 F6.4 --- Motion [0.0/0.64] Moon rate of motion normal to the
lunar limb
189-195 F7.2 --- CAMonn [-179.98/179.98] Moon Contact angle
197-201 F5.3 --- szMoon [0.95/1.1] Moon size
203-208 F6.2 --- PaMoon [0.01/359.94] Moon position angle
210-213 A4 --- CuspMoon Moon Cusp angle
215-217 I3 --- IllMoon Moon illumination
219-220 I2 --- AltMoon [5/82] Moon altitude
222-226 I5 --- Seq [1/13666] Sequential number of the light
curves (CDS)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: asteroid.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 22 A22 "datime" Date Observation date
24- 31 F8.2 s Dur [-44.3/4573.2] Duration of recording
33- 36 I4 --- Np [10/6137] Number of points
38- 43 I6 --- HIP Hipparcos identifier
45- 50 I6 --- SAO SAO identifier
52- 52 I1 --- XZ80Q XZ80Q identifier
54- 62 I9 --- EPIC Kepler2 EPIC identifier
64- 74 A11 --- TYC2 TYC2 identifier
76- 79 I4 --- UCAC2 ? UCAC2 identifier
81- 90 A10 --- UCAC4 UCAC4 identifier
92-104 A13 "d:m:s" Lat Latitude
106-118 A13 "d:m:s" Lon Longitude
120-123 I4 m Alt [-81/3456] Altitude of observer
125-153 A29 --- ObsName Observer name
155-160 I6 --- Num Asteroid number
162-181 A20 --- Name Asteroid name
183-187 I5 --- Seq [101/13667] Sequential number of the light
curves (CDS)
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
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
(End) Dave Herald, G. Landais [CDS] 29-aug-2016