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Date: 19 Feb 2016 23:37:00
Title: Syd. Observatory 1

Sydney Observatory – Part One
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Sydney Observatory was built between 1857 and 1859. Its design combined the practical needs of an observatory and astronomer’s residence with the impressive appearance of a public building in an Italianate style. In keeping with the Observatory’s time-keeping role, the tower and time ball were given greater prominence than the telescope dome. The Observatory in about 1866 and today.
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The Observatory’s original function was to calculate the correct time from the movement of the stars. Before the Observatory was built, there was no accurate time standard in Sydney. The time ball on the tower signalled the time to ships so the officers could check their chronometers, the accurate clocks essential for navigation and for the post office in Martin Place. Sydney Observatory is one of the few places around the world with an operating time ball. The time ball is still raised to the top of its post and dropped at exactly 1.00 pm.
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No sooner than we were in the front door than an enthusiastic young astro-psychics major whisked us up the stairs with another couple of visitors. Bear was dwarfed by a very awesome looking telescope. Soon our young guide had wound the handle to open the ceiling doors of the dome and after a few checks said we could take our turn to look at the sun.
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I was allowed to put my camera lens against the telescope eyepiece and the first image was none to different than looking out of the window. The second lens was a whole new thing for both of us – a mini sunspot. Wow.
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Big sunspots happen on a regular eight year cycle. We were hanging on every word of our guide – what a fascinating subject.
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The HST, being serviced, a rear shot and Cat’s Eye Nebula – an HST image.
The Hubble Space Telescope (HST) was placed into the orbit around the earth by the space shuttle Discovery in 1990. The HST is an optical telescope with a mirror 2.4 metres wide. The great advantage of the HST is that it is above the Earth’s atmosphere. Unlike ground-based telescopes, the HST does not have to contend with the distortion in starlight caused by the atmosphere. Thus images from the HST are up to ten times sharper than from other telescopes. The many images from the HST include some of the stars being formed and others showing the most distant galaxies in the universe.
Inside the Eagle Nebula, taken by HST. Energetic winds from nearby stars have sculpted this tower of gas and dust into an exotic shape. Inside the cold interior of the 9.5 light-year tall tower new stars are likely to be forming.
The Bug Nebula. The fiery, dying star at the centre of this planetary nebula has a temperature of 250,000 Centigrade. During its last gasps the star threw of its outer layers revealing its hot inner core
Stephan’s Quintet. Four of the five galaxies in this compact group are interacting with each other. The blue galaxy at the upper left just happens to lie in the same direction as the others and is much closer to Earth.
Light Echo. In early 2002 the star V838 Monocerotis briefly increased in brightness. Light spreading out from this sudden eruption now illuminates details in the dust surrounding the star. There’s much going on here then.......
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The exhibition here looks at Cook’s observations as well as those made over a century later at the 1874 transit by Sydney Observatory astronomer Henry Chamberlain Russell and his team of illustrious observers.

Voyage of the Endeavour. When Captain Cook set sail on the Endeavour in 1768, his first mission on his three-year epic voyage, was to measure the 1769 transit of Venus in the South Pacific.

Transit of Venus, Tahiti, 3rd of June 1769. James Cook wrote in his logbook: “This day prov’d as favourable to our purpose as we could wish, not a Clowd was to be seen the whole day and the Air was perfectly clear, so that we had every advantage we could desire in Observing the whole passage of the Planet over the Suns disk....”

On arrival in Tahiti, Cook decided to build a fort that he named Fort Venus to protect the observing instruments, the fort consisted of banks of earth, fences and two cannons. It could accommodate forty-five men in tents plus the temporary observatory, the armourer’s forge and a cook’s oven.

Captain Cook spent nearly three years aboard the Endeavour, sailing first to Tahiti to observe the transit of Venus and then south to try and locate Terra australis incognito or ‘Unknown South Land’. He selected the Endeavour for the epic voyage because the former coal vessel “had good carrying capacity, could sail well on the open sea and had shallow draught so they could approach the shore closely”.

Astronomical Quadrant: One of the most important instruments at Tahiti was an astronomical quadrant made by John Bird. It stood in the temporary observatory on a cask filled with wet sand. Cook and Green used the quadrant to obtain the latitude and longitude of Fort Venus. Respected Sydney instrument makers E. Esdaile & Sons made this replica for display at Old Sydney Town, Gosford. It was part of the recreation of Dawes Observatory.(The Portrait Of Captain Cook RN 1782 by John Webber, oil on canvas).

Captain Cook observed the 1769 transit of Venus on the island of Tahiti. His notes describe a ring of light around Venus, known as the ‘penumbra’. “The penumbra was visible during the whole Transit and appeared (sic) to be equal eighth part of Venus’s diameter.”

Mirror telescope. (similar to those used in Fort Venus). Small reflecting (mirror) telescopes were popular in the 18th century. James Cook used one to observe the 1769 transit of Venus. This fine example was made by the respected London instrument maker Dudley Adams (1762-1830). A concave primary mirror collects and focuses starlight in the telescope. There is also a concave secondary mirror to reflect the light back along the tube through a hole in the primary mirror.
A Photoheliograph is a telescope designed to photograph the sun. The English optician John Henry Dallmeyer built a number of them for the 1874 transit, for use at places such as Mauritius, India, the Cape of Good Hope and Australia.
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Amateur astronomer George Hirst was in charge of the instrument for the transit at Woodford in the Blue Mountains. He took many photographs and saw the ‘black drop’ while looking through the small finder telescope. The black drop is a dark thread joining Venus to the edge of the sun. The photoheliograph in the north dome of the Sydney Observatory. (Both pictures above from the transit of Venus in 1892 - note the Janssen apparatus on the observing couch).
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Three transits of Venus as seen from Sydney. The next due in 2117.
Transits of Venus are rare events that occur eight years apart and then not for over a century. They are of special relevance to Australians since James Cook’s voyage to Tahiti to observe the 1769 transit led to the European settlement of the continent. Astronomers of Cook’s time and of the following century were interested in transits of Venus because careful observations allowed them to measure the distance of the Earth from the Sun.

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