On June 3, 1769, navigator Captain James Cook, naturalist Joseph Banks, astronomer Charles Green and naturalist Daniel Solander recorded the transit of Venus from the island of Tahiti during Cook's first voyage around the world. During a transit, Venus appears as a small black disc travelling across the Sun. Transits of Venus occur in a pattern that repeats itself every 243 years, with two transits that are eight years apart, separated by breaks of 121.5 and 105.5 years. These men, along with a crew of scientists, were commissioned by the Royal Society of London for the primary purpose of viewing the transit of Venus. Not only would their findings help expand scientific knowledge, it would help with navigation by accurately calculating the observer's longitude. At this time, longitude was difficult to determine and not always precise. A "secret" mission that followed the transit included the exploration of the South Pacific to find the legendary Terra Australis Incognita or "unknown land of the South."