Telescopes from the Ground Up

Mirrors shape up, drastically improving telescope design

The use of metal mirrors to reflect light, rather than glass lenses to refract light, allowed astronomers to design shorter, more powerful telescopes. This improvement was important: astronomers wanted to be able to maneuver a telescope easily, not spend most of the night fighting to adjust its position or, in the case of the longest, tubeless, reflectors, line up the lenses.

But other changes were in store. It was the 18th century, and the time known as the industrial revolution had begun, spreading manufacturing and industry across Europe. Innovations in technology made people turn to machines to accomplish tasks — including, in the case of telescopes, lens and mirror grinding.

The biggest development in reflecting telescopes — the one that made them as powerful a contender as the refracting telescope — was the creation of the parabolic mirror. The parabolic mirror put an end to spherical aberration, a problem that had caused blurry images since Galileo’s time.

The parabolic mirror, first envisioned by Scottish mathematician and astronomer James Gregory, curves differently than a spherical mirror. The light rays that bounce off the edges and the center all meet at the same point. This creates a clearer image.

Image above: Courtesy Birr Scientific and Heritage Foundation
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