Telescopes from the Ground Up

Herschel’s largest telescopes were designed with a slanting primary mirror that focused the image slightly to the side, so the observer had to lean over the telescope to look at the image. This meant the telescope didn’t need a secondary mirror — all the work involved in making one was eliminated. But it also meant that Herschel had to climb up to a platform above the tall telescope to make his observations.

Though the 40-foot-long telescope was effective for seeing dim objects, it was used only rarely. Herschel used his 20-foot telescope most of the time. The 40-foot version ate up too much observation time — the mirror had to be uncovered, then the telescope needed to be prepared for observation. It also required two assistants, one to help operate it and the other to write down observations. After noting in 1815 that the mirror had become extremely tarnished, Herschel stopped using it.

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Early Reflectors


Portrait of Caroline Herschel.
Caroline Herschel
After assisting her brother, Caroline Herschel becomes an astronomer in her own right.
Read about her