Some highlights of the lick observatory solar eclipse expeditions

Abstract

Over the four decades from January 1889 to August 1932 15 different expeditions were sent out by the Lick Observatory with the primary mission of observing the Sun during the brief moments of a total solar eclipse. During this same interval, considerable advances were made in our understanding of the Sun, but particularly the photosphere and the corona, and a significant portion of this new knowledge came from the investigations that could only be made at the time of a total solar eclipse. The solar corona, the chromosphere and reversing layer were the focus of the Lick Observatory’s visual, photographic, and spectrographic solar investigations. Additional studies included a photographic search for intra-Mercurial planets in the vicinity of the eclipsed Sun, and verification of Einstein’s General Theory of Relativity by the examination of photographic plates for evidence of the deflection of starlight caused by the gravitational field of the Sun. A substantial investment in staff time, financial resources and effort went into the planning and execution of these expeditions, both at the local and international levels. These research ventures were truly expeditions in every sense of the word as obstacles and challenges presented themselves during the planning, staffing and implementation phases. Despite this, the Lick Observatory astronomers had a total of just 39 min of totality spread over all of the eclipses in which to ply their trade. This paper discusses the instrumentation and the scientific highlights of the various Lick Observatory solar eclipse expeditions, and summarizes the overall scientific accomplishments that derived from the expeditions.