HD README Background The 1910 appearance of Halley's comet stimulated much excitement. The HD series plates are of the Comet taken that year. Other than this, little is known about these plates. There is an entry in the Barnard Logbook stating they are "Photographs taken by J.C. Duncan at the Harvard College Observatory (size 5 x 7 and 8 x 10)." This is followed by a log of the plates. How these came to be at Yerkes Observatory has yet to be determined. The Telescopes The logbook entries for the HD series note three different telescopes used: Brashear doublet, Cooke, and a Bausch and Lomb Tessar. The Plates There are 25 plates of this series at Yerkes with plate numbers in the range 7 - 36; all but one are in the Barnard logbook listing. Thus, a number of the HD plates are missing and most likely were never at Yerkes. The Brashear Doublet plates measure 8 x 10-inch (one is slightly smaller) and the Cooke and Tessar plates are 5 x 7-inch. Exposure times range from 4 to 68 minutes. The dates run from 1910-April-20 through 1910-June-8. The Logbook The logbook associated with the HD plates is one section of the Barnard logbook. The book is at the University of Chicago. It has been scanned is available on-line. The Searchable file The comma separated "HD-PLATES.csv" file can be viewed or downloaded to obtain information about the HD plates. The file lists the plates by plate number but can be sorted by other parameters. Any blank cell in the PLATE file indicates that information is missing or has yet to be calculated (for example, the equatorial coordinates of the comet at time of exposure). Description of the columns of the PLATE.csv file Record number - Record number in the catalog Plate series - HD Plate number - Identifying number in the series Date - The date the plate was exposed as recorded. Object - Halley's Comet RA - Right ascension of the plate center (usually blank) Dec - Declination of the plate center (usually blank) Length of exposure - Exposure length (in minutes) Exposure Start - Start time of the exposure as recorded Exposure Mid - Mid-time of the exposure (if computed) Exposure End - End time of the exposure as recorded Time type - Type of time used (E.S.T. = Eastern Standard Time) Emulsion - Emulsion type (manufacturer's name) Plate dimensions - Physical size of the plates, in inches Lens - Telescope used for this plate Observer - Recorded observer (J.C. Duncan) Location - Location of plate when this catalogue was prepared: Yerkes = Yerkes Observatory plate archive Notes - Notes recorded in the log book. File prepared: 2024 February 12 (WO)