Livestream Lecture - July 20, 2022

“Part 2: Travels into Astronomical History with the Antique Telescope Society”


Ken Lum, Antique Telescope Society

In this talk, I will continue my brief history of the telescope as illustrated by pioneering instruments I have visited with the Antique Telescope Society (ATS).

The principles of both refractor and reflector telescopes were invented in the 17th century as shown in my last presentation. Then, the techniques of how to make actual telescopes of both types improved dramatically during the 18th and 19th centuries. However, due to the difficulties of making high quality lens blanks, refractor telescopes remained small, but took advantage of very stable mechanical mounts developed during the Industrial Revolution to evolve into instruments capable of high precision optical measurements that led to very accurate celestial charts, double star measurements, and the measurements of the first parallaxes. But the inability to produce and mount very large refractor lenses plateaued the development of refractors by the 1890s. Today, lens making is largely confined to the production of camera lenses and small refractors.

Reflector telescopes initially used mirrors made from speculum metal, an alloy of tin and copper which could be polished to a highly reflective surface. As far fewer and simpler optical surfaces were required, large reflecting telescopes could be produced which served as big light buckets that were used to search for previously unknown faint deep-sky objects and catalogue their positions. The 19th century saw the development of the first comprehensive catalogues of deep sky objects and stars which we still use today.

The introduction of silver-on-glass mirrors at mid-century coupled with improved precision steel mountings capable of carrying heavy loads finally led to the construction of the first modern reflector telescopes in the early 20th century, a process that continues today.

Finally, the most recent advances involve the introduction of light-weight optics, computerized detectors capable of observing throughout the electromagnetic spectrum, and space-based telescopes freeing us from the limitations imposed by the Earth’s atmosphere.

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