Photoheliograph House 8" South Equatorial House

Photoheliograph House 8" South Equatorial House. . The Very Infrequent Transit of Venus, transit (def) : the apparent passage of a heavenly body across the disc of sun or planet, "Never perhaps, in the world's history, did morning dawn on so many waiting astronomers as it did on the 9th of December, 1874." , H C Russell, Sydney's Government Astronomer, 1874, This building in fact two connected observatories. The small dome housed the Photoheliograph, a special camera to photograph the Sun and the other is the 8 Inch South Equatorial telescope-house. On every clear day for over twenty years, a picture of the Sun was taken within the dome and those 1700 photographic plates still exist. But it was not solar dynamics that was originally under scrutiny here..., Both houses were actually built in anticipation of a more esoteric astronomical event - the transit of Venus. As the positions of Venus and the Earth aligned to allow observation of Venus passing in front of the Sun, 19th century astronomers were given a brief opportunity to calculate distances between the celestial bodies., "The colour was very vivid during the early part of the transit, when the air was very steady. During the latter part when the sun began to boil the planet to my eye... [it turned] a dead black..." , A W Bellfield, Eversleigh, Armidale, 1874, Effectively, these buildings were constructed for scientific observations undertaken during six hours in two days in the entire 19th century. It may seem an expensive venture. However consider that in 1769, when the British Government sent James Cook and the 'Endeavour' on a journey of discovery, it spent 4,000 pounds to observe the previous transit of Venus - from Tahiti. The French were also rushing to the South Pacific. Whichever nation could calculate the distance between the Earth and the Sun could build a more accurate chronometer - a navigational device used to establish position at sea - and thus expand their empire. It was on this journey that Cook carried sealed instructions from the British Admiralty, to be opened only after the transit. Their request? To find the rumoured Great South Land - Terra Australis., A transit of Venus occurred twice in the 19th century, in 1874 and 1882, after which the Photoheliograph was used to record surface behaviour of the sun, and the South Equatorial telescope for observation of comets and minor planets. Another 122 years would pass before Australians would have a chance to witness the next transit of Venus, in 2004.