Harvard College Observatory
![Harvard College Observatory](https://upload.wikimedia.org/wikipedia/commons/6/66/Harvard-Observatory-1899.jpg)
HCO houses a collection of approximately 500,000 astronomical plates taken between the mid-1880s and 1989 (with a gap from 1953–1968). This 100-year coverage is a unique resource for studying temporal variations in the universe. The Digital Access to a Sky Century @ Harvard project is digitally scanning and archiving these photographic plates. Provided by Wikipedia
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Published: 1967
Superior document: Reprints / The Astronomical Observatory of Harvard College : Series II 253
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Published: 1891
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Published: 1887-1890
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Published: 1938
Superior document: Reprints / The Astronomical Observatory of Harvard College : Series I 149
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