On this day in 1769…

Joseph Banks, transit of Venus, Tahiti, Mrs Morgan's Florilegium, Natalie Waddell

Captain James Cook, the Endeavour’s astronomer Charles Green and the rest of the men employed in observing the transit of Venus woke to fine weather and a clear view of the rare celestial event they’d traveled so far to see. Cook wrote in his journal:

“This day prov’d as favourable to our purpose as we could wish, not a Clowd was to be seen the whole day and the Air was perfectly clear, so that we had every advantage we could desire in Observing the whole of the passage of the Planet Venus over the Suns disk.”

The naturalist Joseph Banks, who together with others including third lieutenant John Gore and the ship’s surgeon William Monkhouse had been sent to the nearby island of Mo‘orea to carry out their own observation, wrote:

“Various were the Changes observd in the weather during the course of last night, some one or other of us was up every half hour who constantly informd the rest that it was either clear or Hazey, at day break we rose and soon after had the satisfaction of seeing the sun rise as clear and bright as we could wish him.”

Banks wasn’t particularly interested in the witnessing the spectacle for himself, however, and turned his attentions to other things.

“I then wishd success to the observers Msrs Gore and Monkhouse and repaird to the Island, where I could do the double service of examining the natural produce and buying provisions for my companions who were engagd in so usefull a work.”

In the course of his excursion Banks encountered the chief of Mo‘orea, a man named Ta‘aroa, and his sister Nuna. Following the usual exchange of gifts, he took them to meet his fellow Englishmen and show the Tahitians the purpose of their visit.

Tahiti, transit of Venus, Moorea, Joseph Banks, botanical illustrations, Mrs Morgan's Florilegium, Natalie Waddell,The Tahitians knew Venus by the name Ta‘urua-nui, the beautiful eldest daughter of Atea (the mother of the stars), who had been placed in the sky by the creator god, like the chief of Mo‘orea, named Ta‘aroa.

According to Tahitian legend, as retold in Anne Salmond’s Aphrodite’s Island, “Ta‘urua-nui had sailed her star canoe across the sky, begetting numerous stars and constellations; before guiding the trickster god Hiro on his voyages of exploration. During his visit to the Underworld Ta‘urua-nui had slept with Tafa‘i, another famed explorer, helping him to rescue his father; and a beautiful woman by this name had also been the cause of the wars between Papara and southern Tahiti several generations earlier.”

While Banks’ comrades remained rooted to the spot watching Venus, the naturalist took his leave once again and continued with his explorations, noting that Mo‘orea’s soil was less fertile than that of Tahiti, offering little in the way of useful crops, the land covered over by Pandanus tectorius (right) and Iberis.

It wasn’t a completely wasted journey for Banks, however. He managed to purchase several hog from Ta‘aroa and headed back to camp several hours after Venus had completed its transit and with the Sun now itself about to set. Not long after his return he received some unexpected but most welcome guests.

“Soon after my arrival at the tent 3 hansome girls came off in a canoe to see us, they had been at the tent in the morning with Tarroa, they chatted with us very freely and with very little perswasion agreed to send away their carriage and sleep in [the] tent, a proof of confidence which I have not before met with upon so short an acquaintance.”

The next morning, Banks, Gore, Monkhouse and the rest of the expedition packed up and got ready to make the short trip back to Tahiti “in spite of the intreaties of our fair companions who persuaded us much to stay.”

Over on the main island, despite their best efforts Cook, Green and the men who’d stayed behind at Fort Venus, hadn’t met with the success they’d hoped for. The captain wrote:

“We very distinctly saw an Atmosphere or dusky shade round the body of the Planet which very much disturbed the times of the Contacts particularly the two internal ones. Dr Solander observed as well as Mr Green and my self, and we differ’d from one another in observeing the times of the Contacts much more than could be expected. Mr Greens Telescope and mine were of the same Magnifying power but that of Dr was greater than ours.”

Their attempt to measure the exact moment Venus had first crossed in front of the Sun and the time of its final exit had been hindered by the phenomenon known as the ‘black drop effect‘.

transit of Venus, Charles Green, astronomy, Tahiti, Mrs Morgan's Florilegium, Natalie Waddell,The Royal Society was very disappointed in the results of data collected from the transit and Cook’s report. Not only had the Tahiti observers had trouble with the timing of the stages, their drawings were inconsistent as well.

This was the case with observers stationed elsewhere at other locations, but for what the Society believed to be a failure as far as the Endeavour voyage was concerned, its members decided to blame Green, who died on the way back to England. Cook’s rebuke of the astronomer is said to have been so sharp that it was removed from the Society’s official record of proceedings.

But despite this, the measurements that were obtained helped scientists of the age calculate that the distance from the Earth to the Sun – the astronomical unit – was 92,955,000 miles. Today, modern technology puts the figure at 93,726,900 miles – a difference of eight tenths of one percent.

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