A visit to the observatory

Went to the observatory in (wait for it) Observatory today to collect the mirror from my 8" telescope. It went to Sutherland for re-aluminising, as over the years it has deteriorated rather badly, presumably from the sea air. Although I keep it covered, the salt air penetrates everywhere and I was pleased to be able to take advantage of this free service from the astronomical world. It had to be put in a special box, as nothing must touch the surface of the mirror, which is based on a piece of glass 4cm thick.

The technical man who did the mirror explained how he had had great difficulty in achieving a perfect aluminisation, as the mirror seems to contain different elements in the aluminium to what they are used to. It is placed in a bath of caustic soda, which completely removes the aluminium in readiness for a new coating. This takes place in a vacuum bath which is a twelve-hour process and the mirror comes out like new. However, the damaged portion of mine would not dissolve and so the aluminising had to take place on a not completely satisfactory surface. He put it through the process three times in the weeks it was in Sutherland, but I told him that I would be embarrassed if he spent any more time on a free service, so he brought it back for me to test. If it is not suitable, and I'm sure it will be, he will take it back and try again. What a great service from SALT.

We then had tea with the staff of the observatory and heard a bit about the background. It is built on a slight hill which, in the old days, provided a clear view of Table Bay and the ships in the bay would ask for time signals to set their clocks. A hand pistol would be fired and the ship's captain or navigator, I presume, would look out for the smoke from the gun and set the clock for the arranged time. In those days the few seconds time lapse would not have been a problem. If they wanted a signal at night, they would look for the flash of the powder igniting. Today, the noon gun which is fired every day on Signal Hill is controlled from a machine in one of the rooms at the observatory, a rather inconspicuous bit of paraphernalia almost lost among the multitude of technology which is today's astronomy environment.

There are still a few small telescopes being used there and the photo below shows one of the housings. For those who watched Dr Who in the 60s, you will be forgiven for thinking it is an outsized dalek, a fearsome robot bent on exterminating everyone!