Babcock, Harold Delos (1882-1968)

US astronomer and physicist. He measured the Sun's general magnetic field in 1948 and studied the the relationship between sunspots and local magnetic fields. He also did important work in spectroscopy.

Babcock was born in Edgerton, Wisconsin, and studied electrical engineering at the University of California in Berkeley. In 1909 George Hale invited him to work at the Mount Wilson Observatory near Los Angeles, where he remained until 1948, with breaks during the two world wars.

Babcock made an investigation of the Zeeman effect (whereby a magnetic field causes a substance's spectral lines to be split) in chromium and vanadium - important elements in the solar spectrum. He then produced a revised table of wavelengths for the solar spectrum, published in 1928 and including 22,000 spectral lines (extended 1947 and 1948).

It was in collaboration with his son Horace Welcome Babcock (1912- ) that he succeeded in measuring the solar magnetic field. They used an instrument of their own design, the ‘solar magnometer’, which exploited the Zeeman effect to produce a continuously changing record of the Sun's local magnetic fields.