Paul Sollenberger (1891–1995)

Paul Sollenberger, the U. S. Naval Observatory's first civilian Director of Time Service, died on 22 May 1995 at age 103. Born in Kokomo, Indiana on 14 August 1891, Sollenberger came to the Naval Observatory in 1914 and began work under H. R. Morgan on the 9-inch transit circle. In 1919 he transferred to the Division of Nautical Instruments and Time and in 1928 was put in charge of the Division, a position previously filled by a naval officer. He held this position until his retirement in 1953.

Sollenberger's interest in astronomy began when he took a 12-week course in astronomy at the Marion Normal College, a teacher's college in Marion, Indiana. He was familiar with the Naval Observatory from signs in jewelry stores advertising "Naval Observatory Time," and applied for a job there upon seeing an announcement at his local Post Office.

Sollenberger's contributions to the design of quartz-crystal clocks, chronographs and the photographic zenith tube greatly increased the precision of timekeeping during his tenure. When Sollenberger came to the Naval Observatory, precision pendulum clocks built by Riefler and Shortt were used. They were accurate to only several hundredths of a second per year, and Sollenberger wanted more accuracy. This was found in the quartz crystal clock, but only Bell Laboratories then had such devices. Undaunted, Sollenberger built his own. By 1934 Sollenberger had not only introduced quartz crystal clocks, but also arranged for the automatic transmission of time by these clocks, accurate to one-thousandth of a second. The quartz crystal clocks remained the time standard at the Naval Observatory until atomic clocks were introduced in 1966.

During his career Sollenberger also participated in the World Longitude Operation in San Diego in 1926 and was a member of the Naval Observatory eclipse expedition to the Philippines in 1929. In 1949 he established the Naval Observatory Time Service station with Photographic Zenith Tube (PZT) on the grounds of the Coast Guard radio station in Richmond, Florida, near Miami. The station has remained in operation for nearly 50 years, though the PZT has been superseded by a radio dish used as part of the Very Long Baseline Interferometry (VLBI) network that now determines the Earth rotation parameters.

Sollenberger was an active member of the International Astronomical Union (lAU), and was head of its Commission on Time for several years. Since the French had a strong interest in time, he had extensive contact with them as well as the Greenwich Observatory.

After his retirement, Sollenberger lived in the Miami area. In a lengthy interview in 1987 at the age of 96, Sollenberger clearly recalled the details of his life work at the Naval Observatory. Transcripts and tapes of the interview are deposited in the Library of the Naval Observatory.