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My online copy of the April 2023 edition of Sky & Telescope arrived today and as usual the first thing I read was Roger Sinnott's column 75, 50 & 25 YEARS AGO. The April 1948 edition describes expeditions to "Burma, Siam, China, Japan, Korea, and the Aleutians" to observe an annular eclipse. It was claimed that this would allow the separation of the observers' positions to be determined with errors not exceeding 150 feet and hence measure the figure of the Earth.

(I admit to a rather cynical view of some proposed eclipse projects. In the early 80's, as a student, I attended a talk by someone who was measuring the size of the Sun using total eclipse timings to refute suggestions that it was shrinking at an alarming rate. I came away with the impression that he had come up with a great way to get free trips to exotic locations and observe a rare and magnificent celestial spectacle. He did apparently get results and found that the Sun isn't shrinking. Whew!)

This raises the question as to what can be learned by observing an annular eclipse that cannot be done at least as well with stellar occultations. Both will presumably be subject to uncertainties arising from limb features.

In the column Roger notes "In those days, star sights with a sextant yielded positions accurate to about a mile. LORAN radio navigation was not even that good." But I wonder how well can you do in practice armed with a theodolite? Unfortunately I don't have one to try with.

Robin Stuart