Automatic Plate Measuring facility

Automatic Plate Measuring facility
Name	Automatic Plate Measuring facility
Established	1970s
Location	Cambridge, United Kingdom
Type	Astronomical instrument
Operating agency	Royal Observatory, Manchester University

Automatic Plate Measuring facility The Automatic Plate Measuring facility was a photographic plate digitization instrument and data reduction center that served astronomical, astrometric, and photographic survey communities. It combined precision mechanics, optics, and electronics to scan glass photographic plates produced by observatories such as Palomar Observatory, Kitt Peak National Observatory, Royal Observatory, Greenwich, and institutions like Massachusetts Institute of Technology, Cambridge University and University of Manchester. The facility supported programs linked to projects at Harvard College Observatory, Royal Observatory Edinburgh, and collaborations with agencies including European Space Agency and National Aeronautics and Space Administration.

Overview and Purpose

The facility’s primary purpose was high-precision measurement of positions, magnitudes, and morphological parameters from astronomical photographic plates created by instruments such as the Palomar 48-inch Schmidt Telescope, the UK Schmidt Telescope, and historical surveys like the Palomar Observatory Sky Survey and the Harvard Plate Collection. It enabled work for catalogs such as the Tycho Catalogue, the Guide Star Catalog, and follow-up studies related to missions including Hipparcos and Gaia. The output fed projects at organizations like Royal Astronomical Society, International Astronomical Union, and observatories at Mount Wilson Observatory and Lick Observatory.

History and Development

Development began amid computing advances at institutions like University of Cambridge Computer Laboratory, CERN, and Bell Labs during the 1960s–1970s, influenced by initiatives at Harvard College Observatory and industrial partners such as RCA and Philips. Early designs drew on work from laboratories including National Physical Laboratory (United Kingdom) and collaborations with departments at Imperial College London and Oxford University. Upgrades paralleled digital detector advances exemplified by Charge-coupled device research at Bell Labs and programmatic shifts at European Southern Observatory and Space Telescope Science Institute. Funding and oversight involved entities like Science and Engineering Research Council and committees within Royal Society frameworks.

Technical Design and Components

Mechanically, the system incorporated precision tables, air-bearing stages, and drive systems developed with firms like Rolls-Royce Holdings and Siemens, while optics used lenses and collimators similar to those in instruments at Mount Palomar and William Herschel Telescope. The imaging chain combined photographic plate holders, illumination systems influenced by designs at Jet Propulsion Laboratory, and photomultiplier or CCD readouts that echoed developments at Rutherford Appleton Laboratory and Max Planck Institute for Astronomy. Control electronics relied on minicomputers such as DEC PDP-11 and later VAX systems, and software borrowed algorithms from research at Cambridge University Computer Laboratory, Stanford University, and Massachusetts Institute of Technology. Data storage and archiving referenced formats and practices used by National Archives (United Kingdom) and data centers like Centre de Données astronomiques de Strasbourg.

Operation and Workflow

Operators, often affiliated with University of Cambridge, University of Manchester, and visiting researchers from Harvard College Observatory, prepared plates from collections like the Palomar Observatory Sky Survey and the Harvard Plate Collection. Calibration exposures and fiducial marks tied to standards at National Physical Laboratory (United Kingdom) ensured traceability. Scanning sessions produced pixelized images and centroid measurements processed through reduction pipelines analogous to those at Space Telescope Science Institute and European Southern Observatory. Quality control involved comparisons with catalogs such as SAO Star Catalog, Henry Draper Catalogue, and verification against astrometric frames used by Hipparcos teams.

Calibration, Accuracy, and Limitations

Calibrations used reference stars from catalogs like Tycho Catalogue and UCAC series to correct plate-scale distortions, emulsion nonlinearity, and temperature-dependent mechanical drift observed in facilities including Royal Observatory Edinburgh and Kitt Peak National Observatory. Achieved astrometric accuracies were competitive with contemporaneous instrumentation but limited compared to later Charge-coupled device surveys and missions such as Hipparcos and Gaia. Limitations arose from plate emulsion variability, guiding errors from telescopes such as the Palomar 200-inch Hale Telescope, and digitization noise tied to electronics similar to early DEC systems. Systematic errors required statistical treatments used by researchers at Cambridge University and Max Planck Institute for Astronomy.

Applications and Scientific Impact

The facility contributed to proper motion studies, variable star discoveries, comet and asteroid astrometry supporting work at Minor Planet Center, and long-term variability projects linked to Harvard College Observatory and American Association of Variable Star Observers. Its data supported stellar population analyses used in papers from University of Cambridge, extragalactic surveys feeding work at Harvard–Smithsonian Center for Astrophysics, and historical plate recovery efforts coordinated with Royal Astronomical Society and International Astronomical Union. Outputs were cited in catalogs and follow-up programs connected to Hipparcos, Gaia, and survey initiatives at Sloan Digital Sky Survey.

Preservation and Decommissioning

Preservation efforts involved transferring digitized datasets to archives at institutions like Centre de Données astronomiques de Strasbourg, Harvard College Observatory, and national repositories including British Library and National Archives (United Kingdom). Decommissioning paralleled the shift to digital detectors at European Southern Observatory and space missions such as Hubble Space Telescope, with equipment dispersed to museums like Science Museum, London and research centers such as Rutherford Appleton Laboratory. Legacy datasets continue to support historical research at Harvard–Smithsonian Center for Astrophysics, Royal Observatory, Edinburgh, and projects reconciling photographic archives with modern surveys like Sloan Digital Sky Survey and Pan-STARRS.

Category:Astronomical instruments