The collection of astronomical plates at the Harvard College Observatory contains on the order
of 500,000 plates taken between the mid 1880s and 1989 (with a gap 1953-68). The majority
of these are direct blue plates, taken with a variety of refractors having focal scales of 60-600
arcsec/mm. For objects having blue magnitudes of 15 or brighter, normally from several
hundred to a thousand or more images can be found in the collection; for those with blue
magnitudes of 17, from a few to a hundred or more images can be located. The limit of the
best plates is B 18 mag. Coverage is excellent in both hemispheres of the sky, with the
southern hemisphere having perhaps the advantage.
A few thousand direct plates, mainly blue, were taken with the 1.5-m reflectors located in both
northern and southern hemispheres. These have a focal scale of 26 arcsec/mm. The plates
cover many interesting astronomical objects, such as galaxies, clusters, and nebulae.
The plates with the widest sky coverage (focal scales of 400 to 600 arcsec/mm; some 20% of
the collection) are filed by region, making them very quickly available to the user. The
remainder are accessible through card catalogs, which are substantially complete.
The plate collection also contains a small number of yellow and red plates, with the same
characteristics as the blue plates, but not reaching as faint. However, a variety of emulsions
and filters were used, and thus the compatibility of data from these plates with other data may
Several thousand objective prism spectrum plates are also included in the collection; many of
these were used for the Henry Draper Catalog. The best have a limiting magnitude of 10 (the
limit of the Draper Catalog). Also there is a small (several hundred) collection of slit spectra
of moderate dispersion.
The Plate Stacks also houses a small collection of Daguerreotypes and collodion (wet) plates
taken between 1849 and 1885. These are mainly of historic interest, and include
Daguerreotypes of the moon and sun, and early collodion plates of the planets, stars, the sun,
and solar eclipses. The collection also contains most of the 1200 plates of star clusters and
double stars taken by Benjamin Gould in Cordoba, Argentina, during the 1870s and 1880s.
The Harvard College Observatory welcomes astronomers, writers and researchers to use
the plate collection.
Interested astronomers should contact Lindsay Smith, Curator of Astronomical Photographs at:
Harvard College Observatory
60 Garden Street
Cambridge, MA 02138, U.S.A.
For a more detailed description of the plate series and
some online search forms see the
Harvard University Plates Stacks Digitization Project site and the Digital Access to a Sky Century @ Harvard site.
For further descriptions of the plates, click here.