The transit of Venus
1761 & 1769: First international scientific campaign
A very important discovery concerning Venus was made during the transit of Venus in 1761. Mikhaïl Lomonossov (1711-1765) detected the refraction of the Sun's rays and deduced that only the presence of an atmosphere could explain the fact that one could see a halo of light around the part of Venus that was not yet in front of the solar disk at the start of the transit. The hypothesis that Venus had an atmosphere was proposed for the first time.
This pair of Venus transits was also memorable because it represented the first international scientific campaign. 55 observers followed the phenomenon in 1761 and 151, spread over 77 different locations, in 1769. This enthusiasm was due to the publication, in 1716, of an article by Edmond Halley (1656-1742) about the method to use to determine to Sun-Earth distance during a Venus transit.
He did not have the opportunity to carry out this measure himself during his lifetime, but his proposal was followed and many expeditions were organised to diverse locations in the world. Despite this large number of observations, few results were complete enough to be used and the Sun-Earth distance was still not known with sufficient accuracy.
For example, Captain James Cook (1728-1779), under a mandate from the Royal Society and accompagnied by the astronomer Charles Green (1735-1771) and the naturalist Daniel Solander (1733-1782) among others, sailed all the way to Tahiti to observe the transit of 1769.
After their observations, they continued their voyage to New-Zealand and the East coast of Australia, making their mark in the history textbooks as the first Europeans to set foot on these lands.