Emily Grace: Great Mercury Island & Captain Cook

We left Great Barrier Island and made the mistake of going through the Coville Channel to Great Mercury Island with the tide opposing about 25 knots of wind. This thin bit of sea between Great Barrier and the Coromandel peninsula has swift currents and is known for its rough seas. We had steep waves, a sick captain and a salty boat upon arrival.

Most of Great Mercury Island is owned by a few very wealthy people and we anchored and used moorings right off their mansions and enjoyed "borrowing" their internet. We watched helicopters and beautiful motor launches come and go.

We did go ashore and hiked around to see the sheep, cows and horses and the sweeping views. Emily loved running up and down the green hills and peering over the vistas.

We headed south into Mercury Bay and passed Cooks Bay into Whitianga. You guessed it, more captain Cook. Captain Cook and astronomer Charles Green observed the transit of Mercury at Te Whanganui-a-hei (Mercury Bay) on the Coromandel Peninsula. On the way we passed Needle Rock. Even with my old eyes, I could thread a needle through that hole!

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 on Earth was the first accurate method of determining our distance from the Sun.

Captain James Cook and his expedition members 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, Nicholas Young the cabin boy spotted 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 proved so accurate that some were still being used in the 20th century.

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. The observation was made using the cutting-edge technology of the time, a sextant (invented in 1757). Cook was accompanied by Charles Green, the Royal Society expedition astronomer who died on the homeward journey in 1771.

Cooks Bay

From Cooks journal - "my reasons for putting in here were the hopes of discerning a good harbour and the desire I had of being in some convenient place to observe the Transit of Mercury, which happens on the 9th instant and will be wholly visible here if the day is clear between 5 and 6 o'clock." Cook also named the Whitianga Harbour "River of Mangroves" and this area is still referred to as "The River".

The sighting of the Transit of Mercury is commemorated on Cooks Beach by a cairn of Coromandel granite which tells the story ; "In this bay was anchored 5 Nov 1769, HMS Endeavour, Lieutenant James Cook RN, Commander. He observed the transit of Mercury and named this bay."