High Quality Content by WIKIPEDIA articles! On June 3, 1769, British navigator, Captain James Cook, British astronomer Charles Green and Swedish naturalist Daniel Solander observed and recorded the transit of Venus on 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. This unusual astronomical phenomenon takes place in a pattern that repeats itself every 243 years. It includes two transits that are eight years apart, separated by breaks of 121.5 and 105.5 years (the actual pattern is more complicated and changes over many millennia; the years given will remain valid for a few thousand 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."