What were James Cooks goals? Cook set off for his first journey on August 26, 1768. His main objective was to observe the planet Venus as it passed between the Earth and the Sun. This would help astronomers to calculate the distance of the Sun from the Earth. He also hoped to find the fabled southern continent.Cook's voyage had three aims; to establish an observatory at Tahiti in order to record the transit of Venus (when the planet passed between the earth and the sun), on 3 June 1769. The second aim was to record natural history, led by 25-year-old Joseph Banks.