Captain Cook observes transit of Mercury

Captain Cook assisted his astronomer Charles Green’s observation of the transit of Mercury at Te Whanganui-o-Hei (Mercury Bay) on Coromandel Peninsula.

The inner planets, Mercury and Venus, occasionally pass across the Sun and can be observed as small black dots. Timing these ‘transits’ from different locations was the first accurate method of determining the distance of the Earth from the Sun.

Captain James Cook and his expedition had recently been in Tahiti to observe the transit of Venus, and were now on a mission to search for the rumoured ‘Great Southern Continent’. When stormy seas caused damage to the Endeavour, Cook turned his course towards the land discovered by Dutch seafarer Abel Tasman in 1642. On 6 October 1769, cabin boy Nicholas Young spotted hills behind the east coast of the North Island.

Over the next few months Cook mapped the entire coastline, providing the first-ever ‘outline’ of New Zealand – and establishing that it was not the Great Southern Continent. His charts were so accurate that some were still being used in the 20th century.

During this time Cook and his expedition members had many encounters with Māori, whom Cook described as ‘a brave, war-like people, with sentiments void of treachery’. The Endeavour’s occupants were at first taken for atua (supernatural beings), ancestors, or living visitors from the ancestral land of Hawaiki. Contact was sometimes friendly, but at other times conflict broke out and several Māori were killed by members of the expedition.

Much of Cook’s surveying was done from offshore, but as 9 November approached he sought solid ground from which to observe the transit of Mercury. A cairn on what is now known as Cook’s Beach marks the spot. The observation was made using the cutting-edge technology of the time, a sextant (invented in 1757).

The next transit of Mercury that will be fully visible from New Zealand will occur in 2052.

Image: Captain Cook with sextant (Te Ara)