Astronomical Plates Collection

Astronomical photographic plate NA 8297 from the Maria Mitchell Observatory collection.

Astronomical photographic plate NA 8297 from the Maria Mitchell Observatory collection.

In 2001-2002, the Maria Mitchell Observatory digitized all the 8000+ photographic plates obtained with its 7.5-inch Cooke/Clark refractor during eight decades, from 1913 to 1995 (see Schaefer, B.E., Sky & Telescope, vol. 103, No.3, p. 42). The digitized copies were first put on CD-ROM and later copied to a hard-disk storage device. Their CD or DVD copies are available for the scientific community on request that should be addressed to Dr. Regina Jorgenson.

Most of the plates are 8 x 10 inches, which, with the scale 240 arcsec/mm, corresponds to the field of view 13 deg (RA) x 16 deg (DEC). The richest sky coverage is for Sagittarius, Scutum, and Cygnus.

The limiting (B) magnitude varies with exposure and emulsion and is, typically, between 14 and 16 mag.

Catalog of digitized astronomical plates of Maria Mitchell Observatory

The downloadable catalog file is here. To import the catalog, save the file on your computer as a plain text file. Then open it with Excel as a coma-delimited file and you will have the catalog available for manipulation. The resulting Excel file should be about 700KB in size. The columns of the catalog give: (1) Plate number, (2) Plate’s center Right Ascension (hours), (3) Right Ascension (minutes), (3) Declination (degrees), (4) Exposure time (minutes), (5) Calendar date in Y_M_D format, (6) Julian Date, (7) Emulsion type, (8) Notes. The work on the catalog is still in progress. The current version may have some gaps, which are being filled when detected. We will appreciate any comments/suggestions.

Plates and their Scanned Copies

A commercially available scanner, AgfaScan T5000, customized by the MMO, was used for scanning. Three TIFF image files (about 600 MB in total) were burned on a CD for each plate – the overview scan (65 Mbytes) of the whole plate with resolution of 840 dpi, and two high-resolution (2,500 dpi) scans of the western and eastern halves of the plate (with some overlap). The higher resolution corresponds to about 10 microns on the plate.

The photometric accuracy of the plate copies was investigated in several MMO REU student projects (Bull. Am. Astron. Soc., vol. 33, 2001, abstract 10.13; vol. 36, 2004, abstract 153.03; ASP Conference Series (San Francisco: Astronomical Society of the Pacific), Vol. 338, 2005, p.359), with the conclusion that the scanning typically introduced less than 0.05m additional uncertainty for stars not too close to the plate limit.