'Station near Cairo for Observing the Transit of Venus', 1874.
© Science Museum / Science & Society Picture Library
Engraving taken from the 'Illustrated London News'. The transit of Venus acros the face of the Sun is a comparatively rare astronomical event; that of 1874 was keenly anticipated, with a number of expeditions sent to observe and photograph the occurrence, including one to Cairo, Egypt. The transit is important astronomically because if it is observed from various locations on the Earth's surface it is posible to calculate the solar parallax (the distance from the Earth to the Sun). Because of this, Captain James Cook was sent to Tahiti to observe the transit previous to that of 1874, which occurred in 1769. The next transit of Venus will be in 2004.