40-in-FRy README Background George W. Ritchey was a a gifted mechanical and optical engineer that played a key role in the early development of Yerkes Observatory. He perfected the technique of obtaining high quality photographs with a visually corrected refracting telescope, in this case the Yerkes 40-inch refractor, using iso- chromatic plates and a yellow filter. These plates constitute the the FRy (Forty-inch Ritchey) series (which should not be confused with the Ry plate series of plates that Ritchey took with the 24-inch reflector he designed). The Telescopes: All FRy plates were taken with the well-known Yerkes refractor, a visually- corrected doublet of 40 inches (101 cm) clear aperture. It has a focal length of 744 inches (1890 cm) which gives a scale of 10.65"/mm. A detailed description was given by Hale (Hale, G. E. 1897, Astrophysical Journal, vol. 6, p.37. The location of Yerkes Observatory is: longitude = 88° 33’ W, latitude = 42° 34’ N. The Plates Ritchey rook over 65 plates taken in 1900 and 1901. The exact number is uncertain. Not all plates were entered in the logbook, which was compiled in the 1930s, and it is likely that Ritchey took some of his better photographs with him when he left Yerkes in 1906 to work at Mt. Wilson. The earliest plates are mostly 3¼ x 4¼-inch in size while the later ones measure 8 x 10-inch They were Cramer Instantaneous Isochromatic plates combined with a yellow filter (which was referred to as a screen). Further details can be found in Ritchey, Astrophys. J., 12, 352, 1900 and Ritchey, Publ. Yerkes Obs.,2, 1904. The Logbooks The logbook for the FRy plates are in a section in the Barnard logbook. That book was prepared in the mid-1930s and is a compilation of the plates taken by E. E. Barnard supplemented with a number of other early plate series the Observatory then held, including those by Ritchey (on pages 98r-98t). The Searchable files There are two csv files that can be viewed or downloaded to search for plates of interest. The “Full.csv” file lists the plates by plate number. The “By-Dec.csv” file is the Full.csv file sorted by decreasing declination for the star fields followed by the moon plates. This file provides a quicker way to see if the collection contains plates of interest. An "Additional-Notes.csv” file provides any detailed notes on a plate from the logbook that are not included in the notes of the Full.CSV file. Any cell in a csv file that is blank indicates there is no information available or it has yet to be calculated (for example, a time of mid-exposure when the start time and end time are known). Description of the columns of the csv files Record number - Record number in the catalog Plate series - FRy Plate number - Identifying number of the plate Date - The date the plate was exposed as recorded. Object - The target field or object of the exposure. RA - Right ascension of the plate center (for star fields) Dec - Declination of the plate center (for star fields) Length of exposure - Exposure length (in minutes for star plates, in seconds for moon plates) Exposure Start - Start time of the exposure (when recorded) Exposure Mid - Mid-time of the exposure (not yet calculated) Exposure End - End time of the exposure (when recorded) Time type - Type of time used: C.S.T = Central Standard time, Sid = local sidereal time) Emulsion + Filter - Emulsion type and filter used (when recorded). Cramer isochromatic plate with a yellow filter can be assumed when there is no entry Plate dimensions - Physical size of the plate, in inches Observer - George Ritchey Location - Location of plate when this catalogue was prepared: Yerkes, U. Chicago Blank indicates that plate not in vault. Notes - Notes recorded in the log book. Longer notes are in the Additional- Notes.CSV file File prepared: 2022 October 12