Making a Telescope

CHAPTER 18 – Sky-Watching Discovery II: Making a Telescope

In 1981, Dominic, and I decided to build a telescope. Dominic loved astronomy and spent night after night making star maps and identifying stars from Norton’s Star Atlas. Hastings, Hawkes Bay, New Zealand was ideal for star-gazing. The night skies were usually clear of clouds, even in winter. The city did not produce too much light glow and, of course, New Zealand had no continental haze.

We decided upon an 8″ reflector. I would grind the mirror and Dominic would research, plan and design the components. I managed to get two blanks of 1″ thick glass locally for $10; we ordered the diagonal mirror, eyepieces and holder from the USA for $250; and Dominic had an equatorial stand made by a retired engineer for the princely sum of $60. The aluminium tube cost $10. I spent months grinding the mirror. And after grinding, came hours of fine polishing with wood pitch and jeweller’s rouge.

Soon it was time to apply the Foucault Test to the mirror using candle, razorblade, and water. One of us poured water over the mirror to keep it wet, while the other tried to catch the patterns of a light ray diffracted by the razor-blade and reflected on the mirror. Amazingly, one could detect down to 1/8 of wavelength of light of surface variations on the glass. One could determine then whether one had shaped a parabola on the glass. After hours of trial and error tests we achieved the best parabola we could get for our equipment.

Finally the mirror had to be silvered. Dominic was determined that we should have a silver mirror rather than an aluminium one. One could get the mirror sprayed with aluminium but it was less reflective than silver. On the other hand, silver was difficult to apply and less permanent. So, I had to visit the pharmacies and chemist shops of Hawkes Bay, for silver nitrate solution, which many chemists no longer used. The mirror had to be perfectly cleaned by concentrated acid, and ammonia was added to a mixture of water and silver nitrate to cause the silver to precipitate. After many failures, finally we had a silvered mirror, even if a bit milky.

All the parts were assembled and aligned, and behold, it worked! The moon, Jupiter’s red spot, Saturn’s rings, and the Milky Way, all became wonders of the night and a source of enjoyment for family and visitors.

We were both immensely proud of this achievement. I then sought the company of others who enjoyed night-sky viewing, and joined the local astronomy club only to find that meetings were dominated by philosophising about the nature of deep space and the universe. No one seemed to view the sky itself.

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