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The Naval Observatory Library Today

Dr. Kenneth J. Johnston, Scientific Director

U.S. Naval Observatory


The library is an essential tool in the everyday working of the Observatory. Although the library has been restored to its appearance in the 1890's, its contents are needed for the Observatory's mission: determining time both atomic and astronomical and charting the positions of celestial objects. In the 1890's the accuracies achieved in measuring these phenomena were 0.1 seconds/day of time and 0.3 seconds of arc. The units of time are now in one billionth of a second/day and of the positions of celestial bodies one thousandth of a second of arc. Many of the improvements in accuracy have been accomplished in this library. The library collection records the information on the basic and applied scientific understanding of the techniques that are and were used to make these measurements; the previous measurements that were made as well as predictions for the future. All scientific results are based on knowledge of past accomplishments. Using this knowledge, improved methods are devised as well as using previous measurements to further our knowledge. These old measurements, although not as accurate as those currently made are invaluable. For example, catalogs of star positions that were made in 1900 with accuracies of 0.3 arc second are used today to determine stellar proper motions. With a baseline of 100 years, an accuracy of 0.003 arcseconds/year can be achieved. This is comparable to the accuracy achieved by present day methods. We scientists look forward to using the same old books, journals and magazines as well as those acquired in the future to accomplish the mission of the Observatory in both operations and research.

USNO Master Clock Time
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