Draft:Theodore Walraven

• Comment: Please correct all the sources to full citations, see WP:REF. As written no volunteer reviewer can verify anything here. Ldm1954 (talk) 15:18, 6 November 2025 (UTC)

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Theodore Fjeda Walraven (July 26th, 1916-January 13th, 2008) was a Dutch astronomer and photometrist, best known for his work and advancements in photometry and polarization, such as his involvement in making a polarized map of the Crab Nebula.

Biography

Th. F. Walraven was born in Amsterdam on July 26th, 1916. There is little to no record of his early life. He published his first paper, along with David Koelbloed in 1938, which was titled "Some Observations of the Spectrum of γ Cassiopeiae", which was posted on the Bulletin of the Astronomical Institutes of the Netherlands, volume 8, number 314, on pages 299-304. He received a PhD from the University of Amsterdam in 1948. His thesis was titled "The Line Spectrum of Delta Cephei", which was supervised by Anton Pannekoek, and approved by Herman Zanstra. In 1946, he joined the Leiden Observatory, where he eventually became the superintendent in 1950. He would continue working at the Leiden Observatory, publishing many papers, until he eventually retired as a Professor of Astronomy in 1980. After his retirement, he and his wife, Johanna H. Walraven moved to Cornelia, South Africa, where they continued their study of variable stars. When his wife died in 1989, he continued some of his work. He gave one last lecture as a guest at Leiden in 1990 where he brought multicolor observation of Al Velorum, a variable star which he and his wife spent much of their time observing. He also published his final paper in 2000 . On Sunday, January 13th, 2008, Theodore Walraven passed away at his home in South Africa.

Inventions

In 1956, while working with Leiden director Jan Oort, Walraven worked to make the photometer polarimeter. This device was the first instrument at Leiden that allowed for simultaneous measuring of light intensity and light polarization, and was essential in their work with the Crab Nebula, and the confirmation of synchrotron radiation.

Walraven's later, and most important invention, was the 5 channel photometer, aka, the Walraven photometer. It is a photometer able to simultaneously measure 5 passbands, V, B, L, U, and W. These bands were chosen as a photoelectric analogue of the Barbier-Chalonge-Divan classification. It used a system of quartz and calcite crystals to filter and produce 5 well defined and stable passbands. They installed this photometer on the newly-built 91 cm reflecting telescope called "Lightcollector". This system was in operation for 32 years.

He had later attempts to make advancements, such as the radial velocity photometer he developed in the late 1960's. This attempt ultimately failed, as the Dutch Science Foundation ZWO did not continue to support his work on that particular device any further. He also made more advancements on his multi channel photometry work, developing a 12 channel spectrum scanner, where 12 passbands could be studied, instead of the previous 5. This invention of his never made it to a more general use market, but rather, was used by him and his wife during their research in Africa.