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Kaj Aa. Strand
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BIOGRAPHY

Scientific Director, U.S. Naval Observatory, Washington, D.C., 1963–77. Editor of Basic Astronomical Data; Vistas in Astronomy.

Primary Contributions (1)
Diagram illustrating how astronomers calculate the distance to a star using parallax: Earth is shown in two positions on opposite sides of its orbit around the Sun, with lines extending to a nearby star X and further to distant background stars. The apparent shift in star X's position, measured as angle A, is used to determine its distance, with the baseline labeled as 186,000,000 miles.
Parallax
Parallax, in astronomy, the difference in direction of a celestial object as seen by an observer from two widely separated points. The measurement of parallax is used directly to find the distance of the body from Earth (geocentric parallax) and from the Sun (heliocentric parallax). The two…
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