Brouwer, Dirk

(b. Rotterdam, Netherlands, 1 September 1902; d. New Haven, Connecticut, 31 January 1966)

astronomy.

Brouwer worked mainly in celestial mechanics, making elegant theoretical contributions but also pioneering in the use of high-speed digital computers to solve its problems with previously unattainable accuracy.

The fourth of six children born to Martinus Brouwer, a government employee, and his wife Louisa van Wamelen, Brouwer studied under Willem de Sitter at the University of Leiden, where he received the Ph.D. in 1927. He then came to the United States on a year’s fellowship and joined the faculty of Yale University in 1928 as an instructor. In 1941 he became both professor of astronomy and successor to Frank Schlesinger as director of the Yale Observatory, posts he held, together with the editorship of the Astronomical Journal, for the rest of his life. He was married in 1928 to Johanna de Graaf and became an American citizen in 1937.

At Yale, Brouwer first assisted Ernest William Brown in his search for differences between predicted and observed positions of the moon that would reveal changes in the earth’s rotation. In 1930 he found that some of the differences were due to incorrectly located reference stars. To get better positions for these stars, Brouwer turned to asteroids (1935), later investigating the origins of these small bodies in a paper extending the membership in Hirayama’s families (1951) and one on Kirkwood’s gaps (1963).

After Brown’s death in 1938, Brouwer took up more general orbital problems. Papers he published in 1938 and 1946 formed the basis for a direct determination of planetary positions by stepwise numerical integration, which was realized in Coordinates of the Five Outer Planets, 1653–2060, (1951), written jointly with Wallace John Eckert and Gerald Maurice Clemence. This was the first astronomical problem to be solved through use of a high-speed computer. In an address delivered in 1955, when he was awarded the Gold Medal of the Royal Astronomical Society for his outstanding contributions to celestial mechanics, Brouwer outlined the way in which computer techniques were changing his field.

The advent of artificial earth satellites in 1957 provided an application for two theoretical papers Brouwer had written in 1946 and 1947, and led to two more (1959, 1961) of significant merit.

Brouwer was an active member of the International Astronomical Union and influential in its adoption of a new set of fundamental astronomical constants in 1964. It was he who suggested the name for Ephemeris Time (1950) and provided data on the way it diverged from Universal Time between 1820 and 1950 (1952). He was elected to the National Academy of Sciences in 1951, given an honorary D.Sc. by the University of La Plata in 1961, and awarded the Bruce Medal of the Astronomical Society of the Pacific in 1966.

BIBLIOGRAPHY

I. Original Works. Brouwer’s dissertation, “Diskussie van de Waarnemingen van Satellieten I, II en III van Jupiter,” was presented to the University of Leiden in April 1927 and incorporated into the paper “Discussion of Observations of Jupiter’s Satellites Made at Johannesburg in the Years 1908–1926,” in Annalen van de Sterrewacht te Leiden, 16 (1928), 7–99, with erratum on 99. Other works, referred to in text, are “Discussion of the Annual Term in the Residuals in the Moon’s Longitude,” in Astronomical Journal, 40 (1930), 161–168; “On the Determination of Systematic Corrections to Star Positions from Observations of Minor Planets,” ibid., 44 (1935), 57–63; “The Use of Rectangular Coordinates in the Differential Correction of Orbits,” ibid., 46 (1938), 125–132, written with W. J. Eckert; “On the Accumulation of Errors in Numerical Integration,” ibid., 149–153; “Integration of the Equations of General Planetary Theory in Rectangular Coordinates,” ibid., 51 (1946), 37–43; “The Motion of a Particle of Negligible Mass Under the Gravitational Attraction of a Spheroid,” ibid., 223–231; “A Survey of the Dynamics of Close Binary Systems,” ibid., 52 (1947), 57–63; Coordinates of the Five Outer Planets, 1653–2060, Vol. XII of Astronomical Papers Prepared for Use of the American Ephemeris and Nautical Almanac (Washington, D.C., 1951), written with W. J. Eckert and G. M. Clemence; “Families of Minor Planets and Related Distributional Problems,” in Astronomical Journal, 55 (1951), 162–163; “A Study of the Changes in the Rate of Rotation of the Earth,” ibid., 57 (1952), 125–146; “The Motions of the Outer Planets,” in MonthlyNotices of the Royal Astronomical Society (London), 115 (1956), 221–235, the George Darwin lecture delivered by Brouwer on 6 April 1955, when he received the Gold Medal of the Royal Astronomical Society; “Solution of the Problem of the Artificial Satellite Without Drag,” in Astronomical Journal, 64 (1959), 378–397, errata in 65 (1960), 108; “Theoretical Evaluation of Atmospheric Drag Effects in the Motion of an Artificial Satellite,” ibid., 66 (1961), 193–225, appendix on 264–265, both written with Gen-ichiro Hori; and “The Problem of the Kirkwood Gaps in the Asteroid Belt,” ibid., 68 (1963), 152–159.

Brouwer also wrote two textbooks: Spherographical Navigation (New York, 1944), written with Frederic W. Keator and Drury A. McMillen; and Methods of Celestial Mechanics (New York, 1961), written with Gerald M. Clemence.

A complete list of Brouwer’s works, with 156 items, follows Clemence’s biographical memoir (see below).

II. Secondary Literature. The adoption of Brouwer’s suggestion that time based on the year rather than the day be called Ephemeris Time is recorded in “Colloque Internationale sur les Constantes Fondamentales de l’Astronoimie, Procès-verbaux des séances,” in Bulletin astronomique, 2nd ser., 15 (1949 for 1950), 283; the citation made by John Jackson in announcing the award of the Gold Medal of the Royal Astronomical Society to Brouwer was printed in Monthly Notices of the Royal Astronomical Society, 115 (1955), 199–202; Louis George Henyey’s “Posthumous Award of the Bruce Gold Medal to Professor Dirk Brouwer” appeared in Publications of the Astronomical Society of the Pacific, 78 (1966), 194–197; John Michael Anthony Danby wrote an obituary notice in Quarterly Journal of the Royal Astronomical Society (London), 8 (1967), 84–88; and Gerald Maurice Clemence’s memoir can be found in Biographical Memoirs. National Academy of Sciences, Washington, 40 (1969), with portrait and list of publications.

Sally H. Dieke