The first voyage of James Cook was a combined Royal Navy and Royal Society expedition to the south Pacific Ocean aboard HMS Endeavour, from 1768 to 1771. It was the first of three Pacific voyages of which Cook was the commander. The aims of this first expedition were to observe the 1769 transit of Venus across the Sun (3–4 June of that year), and to seek evidence of the postulated Terra Australis Incognita or "unknown southern land".