On Sunday 28 July Sydney City Skywatchers were fortunate to have Ron Ekers, CSIRO Fellow, inform a walking tour along the cliff tops of Dover Heights, Sydney, the birthplace of radio astronomy. Ron is a much awarded radio astronomer who was the first director of the Very Large Array and the Foundation Director of the Australia Telescope National Facility. He has worked in the Netherlands and the USA. Jay Ekers also attended the talk and it was interesting to hear that she had also worked in astronomy on the mathematical reduction of data. Helen Sim, also from CSIRO, attended the walk and posted this report & request for information.
We began our tour from Rodney Reserve where participants sighted two whales migrating north, saw a ship in the distance on fire and were given a tour of the South Head Signal Station by the Marine Rescue volunteers. The officers told us that whilst the burning ship sank, thankfully the crew escaped harm.
As a doctoral student in the early 1960s at ANU Ron Ekers was supervised by John Bolton. Bolton was instrumental in and Ron spoke about his enthusiasm for the development of radio astronomy. Ron produced the following summary for the walking tour (CSIRO has an expanded version as part of its heritage series) :
Radio Astronomy at Dover Heights
The Dover Heights site was used by scientists from the CSIRO for experimental radar work. After the war ended CSIRO used the site as a field station for radio astronomy. The four discoveries made here at Dover Heights changed our understanding of the Universe.
The Cliff Interferometer
In 1946 a telescope was constructed on the cliff at Dover Heights to measure the interference between the direct waves and those reflected by the sea. This cliff interferometer was built to locate the origin of the solar radio emission and to identify the radio stars. The idea of a cliff interferometer came from multiple path interference already seen in ship-borne radar in WWII and used to improve positional information.
In 1946 Ruby Payne Scott used the cliff interferometer to discover that radio waves from the sun were coming from sunspots. Payne Scott’s story is fascinating and is now available in a book by Miller Goss, recently released in paperback.
In 1948 John Bolton and his colleagues at CSIRO were able to measure positions accurately enough to identify three of the strongest of the mysterious discrete sources of radio emission which up until this time were thought to be stars emitting radio waves like the sun. One was the Crab nebula, the remnant of a star that the Chinese had seen explode in 1054 AD and which was still producing radio waves.
The other two radio sources were an even greater surprise. Centaurus A and Virgo A (strongest sources of radio emission in the constellations of Centaurus and Virgo) had conspicuous bright optical identifications which were galaxies – not stars! Galaxies, far outside our own milky way but undergoing such a violent explosion that they were among the brightest objects in the radio sky and became the most luminous sources known in the universe.
The Hole-In the- Ground Antenna
In 1951 John Bolton, Gordon Stanley and Bruce Slee wanted a more powerful instrument but CSIRO did not have the necessary funding. They decided to build a new radio telescope by themselves. They spent their lunchtimes excavating a 21.9 metre diameter dish-shaped hole in the sand then metal strips from packing cases were laid across the surface to provide a reflecting surface which focussed the radio waves at the top of a mast at the centre of the antenna. This radio telescope detected a strong radio source in the constellation of Sagittarius. The radio astronomers had discovered the radio emission from the black hole at the very centre of our Galaxy!
The Dover Heights Memorial
To celebrate the history and achievements of the Dover Heights site CSIRO installed a full-size replica of the 8-element Yagi used in 1951.
The memorial was opened on 20 July 2003 by Her Excellency Professor Marie Bashir, Governor of New South Wales. (Ron Ekers, CSIRO)
One of the most spectacular yet mysterious sections of our walk was Diamond Bay. Where did its name come from and where did this stone portal lead?
South Head Signal Station
This is a remarkable site of continuous signalling for over two hundred and twenty three years. Past Signal Masters included Captain John Hunter (1790), Daniel Southwell (1790) and Robert Watson (1791) after whom Watson’s Bay is named. Our walk participants were able to go inside the Signal Station and see its operations which have been by volunteers since 1992.
The Signal Station has a close connection with Sydney Observatory’s Fort Phillip Signal Station. From the 1830s it communicated with Fort Phillip Signal Station using flags to send messages of ship arrivals to the colony. Flagstaffs were located along the river and were able to send messages of ship arrivals to Government House in Parramatta very efficiently.
South Head Battery
Whilst it was difficult to see the remans of the original battery built in 1892 as one of three defence sites, evidence of the 1930s structure and WWII is clear.
The Wreck of the Dunbar
Our last stop was the anchor of the Dunbar. This 1857 marine disaster had only one survivor and was a catastrophe for the colony. It may have spurred on completion of Sydney Observatory so that the Time Ball could be dropped for ships to set their chronometers by.
Sydney Observatory and Sydney City Skywatchers work together to provide astronomy events and tours to enthusiasts.
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