Data Set Overview :  This data set is intended to include all reported timings of observed asteroid, planet, and planetary satellite occultation events, as well as axes derived from those timings by David W. Dunham and David Herald. Most of these timings are unpublished and have been collected by Dunham and Herald. This version is complete through April 2011.  The sizes (major and minor axes) derived from the occultation timing data are the result of an analysis program by Dunham and Herald, applied consistently to all the occultation events.   Occultations Analysis Program :  As input to the analysis, observers submit a report to the program including disappearance and reappearance timings, observatory location, and observing conditions. The observations are reduced using the Besselian fundamental plane as the reference plane. The basic methodology is as follows.  - The position of the asteroid is computed at three intervals, centered on the nominal mid time of the observed occultation. The positions are converted to (x,y) coordinates on the fundamental plane, expressed as a quadratic expression. These calculations are performed in the J2000 reference frame.  - The (x,y) position of each observer on the fundamental plane is computed at each of their event times. The orientation of the fundamental plane is referenced to the apparent equinox of date for this purpose.  - All of the observer positions are referenced to a moving reference frame that is fixed relative to the asteroid. This reference frame has a nominal zero defined by the observer coordinates associated with the first observation. The motion of the reference frame is that of the asteroid.  - The fit of an ellipse to the observations occurs in this moving reference frame (which is fixed relative to the asteroid). The calculations are performed in units of earth radii, and converted to km for output purposes.  - The astrometric position of the asteroid is obtained by combining the motion of the moving reference frame with the location of the fitted ellipse on that reference frame, to obtain the time when the asteroid was closest to the geocenter - from which the time, separation and position angle of the asteroid relative to the star are derived.  This methodology takes full account of the motions of the asteroid and the observers.   Data :  The asteroid occultation timing data are collected into two files. The occlist file lists a total of 1872 occultations, one occultation per line, along with the identification of the asteroid and star, and additional information about the star including RA and dec. These lines also include the major and minor axes derived from the timings for that occultation, if any, along with information about the analysis. The list is chronological, with an occultation ID assigned to each one. The occtimings file lists the individual timings measured for each occultation, with one disappearance and reappearance per line, as well as information about the observing site and the observational circumstances. The latitude, longitude, and elevation of each site are included.  Two analogous files, occsatlist and occsattime, with occultation data on planets and planetary satellites, are also included.   Ancillary Data :  Summary files, occsummary.tab and occsatsummary.tab, contain the major and minor axes and position angles from the elliptical or circular fits, extracted from occlist and occsatlist respectively.  Graphics image files show plots of the occultation fits for many of the occultations. These image files are located in the document directory, and are accompanied by a descriptive text file 0Graphics.asc explaining how the plots are to be read. The filenames of the image files concatenate the asteroid number, asteroid name or provisional designation, and occultation date.   Modification History :  The first version of this data set, introduced in 2003, included occultations only through 1998. The update of 2004 not only adds occultations through March 1, 2004, but also provides a more systematic arrangement of the data. The data set was again updated in 2005, 2006, 2007, 2008, 2009, and 2010. The number of occultations included in each successive version is as follows:  Year: Version: Number of occultations: 2003 V1.0 183 2004 V2.0 524 2005 V3.0 680 2006 V4.0 865 2007 V5.0 1055 2008 V6.0 1203 2009 V7.0 1417 2010 V8.0 1662 2011 V9.0 1935

Confidence Level Overview : This data set is compiled from the observations made by a large number of observers. Indications to the confidence level of each observation are included in the data files.