Scientists attempted to measure the astronomical unit by observing the transit of Venus in 1769.
Notes on verification
Multiple authoritative sources including Library of Congress, Ohio State University astronomy department, and peer-reviewed arxiv paper all corroborate the specific details: the 1769 transit was observed to measure the astronomical unit, Halley proposed the method in 1716, Cook observed from Tahiti, and the calculation achieved ~1% accuracy. The consistency across academic and institutional sources strongly supports all key claims.
Sources
- 1874 Transit of Venus Expedition to Hawaii (wikipedia)