I need to set up a reminder to catch this because Venus going visibly across the Sun is an important historical and scientific matter.
The Guardian gives a solid rundown here.
Astronomers in the 18th Century sent scores of people all over the world to measure the event from numerous locations. Then they compiled the data and used it to figure out the distance between the Earth and Sun. They concluded it was 93 to 97 million miles. A pretty impressive result without the assistance of computers, calculators or difference engines! Ninety-three million miles (160 million kilometers) is the accepted distance plus it’s the definition of one Astronomical Unit (aka an AU). Afterwards, astronomers used this finding to extrapolate the size of our solar system.
The Venus transit dovetails into some history involving the data gathering team led by the British Navy’s Leftenant Cook. His orders were to sail the HMS Endeavour to Tahiti and set up equipment to measure the event; Cook was also educated enough to use it. As per a special I saw on PBS/History Channel, Cook’s interaction with the Tahitians was unusually progressive since most 18th Century Europeans would arrive, bully the residents, take what they wanted and leave. Cook instead ordered his crew to cooperate and negotiate with the Tahitians for they were going to be around a while. This worked out pretty well, especially after the sailors discovered they could trade minor supplies (nails, rope, etc.) for sex. According to Cook’s accounts, the Tahitians were kleptomaniacs and they almost wrecked the expedition when one of them stole the telescope as the deadline neared. Successful diplomacy prevented this from escalating into a fight.
With the Venus transit completed, the Endeavour sailed west (and probably south) to New Zealand where the crew mapped the islands/coastlines for about six months. It was there Cook opened his secret orders from the admiralty. He was instructed to take the ship south to the 40th parallel and go east until they hit land. Cartographers, scientists and others believed there had to be a continent or two in the area. They thought the planet required a counterweight for the existing landmasses; I wonder how these people would’ve reacted to the Pangea theory.
On April 20, 1770 the HMS Endeavour succeeded when the vessel’s lookout spotted the land we know today as Australia.