Looking south in Sydney Observatory’s basement in about late 1982. Photo Nick Lomb
in July 1982, when Sydney Observatory came under the auspices of the Powerhouse Museum, it looked very different to what it does today. Here are a couple of pictures of the Observatory’s basement before the changes brought about by the Observatory’s new role began in earnest.
In the early 1980s the Observatory’s basement was a magical place housing lots of clocks and related devices that could be both heard and seen. Evening and Wednesday afternoon visitors were taken there to look at two large models – one showed the planets circling the Sun while the other was a model of the Earth and the Moon circling the Sun. Visitors were fascinated by these devices as it is so much easier to understand these motions including the seasons, phases of the Moon and eclipses when looking at three-dimensional models.
In the above photograph the Sun, Earth, Moon model (tellurium) is in the foreground. It was built in the Observatory’s workshop in 1952 and though no longer on display, it remains in the collection of the Powerhouse Museum.
Against the back wall we can see the Shortt 49 slave clock. The Shortt clocks were the most accurate mechanical clocks ever made with a daily accuracy of about 0.01 seconds. They consisted of a master clock, in which the pendulum oscillated in a vacuum, and a slave clock, the pendulum of which was corrected every 30 seconds by the master clock. Sydney Observatory had two of these clocks with both slaves on show in the basement, while the masters were in a separate temperature-controlled room. Incidentally, in those low tech and low budget times, the temperature control consisted of a continuously switched on electric bar heater that had been rewired for low wattage.
The old refrigerator next to the slave clock was used not to store beer or other beverages for the astronomers, but the photographic plates used for photographing the sky. The plates needed to be kept cold before they were exposed.
The boxes on the left housed equipment relating to the clocks. The box at the end was internally lit and had a glass top so that visitors could see the relays that sent out the six-dot signal or the ‘pips’ to radio stations on the hour. The clock that controlled these relays was an atomic clock housed upstairs, but the mechanical clocks in the basement were kept going as part of a complex backup system. On rare occasions the pips were not sent out and immediately the radio stations called and complained. The problem was usually due to a telephone line failure.
Looking north in Sydney Observatory’s basement in about late 1982. Photo Nick Lomb
In the photo above we are looking in the opposite direction and we have a better view of the planet model or orrery that showed the relative rates that the planets move around the Sun, which was represented by an incandescent light globe.
The poor state of the painting on the ceiling is rather obvious. The story was that the Observatory had been hurriedly painted for the 1973 General Assembly of the International Astronomical Union that was held in Sydney with the Government Astronomer Harley Wood as the chair of its organising committee. Somehow the painters made such a mess of the basement ceiling that the paint peeled off soon afterwards.
The room at the end of the basement with light escaping through the glass panel in its door was the temperature-controlled room that housed the two Shortt free-pendulum master clocks. Just to the left of the door with the glass panel is a small dark room used to develop the photographs of the sky taken with the Observatory’s astrographic telescope and its attached camera.
Today, the basement, also known as the Discovery Room, is a lecture room used for adult education classes and by the Sydney City Skywatchers for their monthly meetings. If you have not been to the basement, come along on the first Monday of each month at 6:30pm to a meeting of the Skywatchers. All are welcome and there is only a token payment of $2 requested for supper and a raffle ticket.