The telescope design that Galileo championed is not the one that is used in astronomical telescopes today. The Galilean telescope fell out of favour with astronomers shortly after Galileo's death [_1_] . Modern refracting telescopes are actually based on Johannes Kepler's design. But Kepler never built a telescope. The first Keplerian telescope was built by a Jesuit priest, Christopher Scheiner, some time between 1613 and 1617 (see Timeline of the Telescope). The Galilean design used in early telescopes was discarded largely because the Kepler/Scheiner telescope provided a dramatic improvement in the field of view. The image below shows the fields of view of a 20 power Galilean telescope and a 20 power Kepler/Scheiner telescope. The outside perimeter is the field of view of a Kepler-Scheiner telescope and the small lense in the center of the image is the field of view of the Galilean telescope [_2_] . As the power of these telescopes is increased the field of view decreases correspondingly. At higher powers, the field of view of the Galilean telescope would be so narrow that it would be effectively useless.
When Scheiner built the first modern astronomical telescope he was doing what any other scientist of his time could have done, but didn't. In Dioptrice, Kepler had discussed a telescope design with a positive ( convex or plano-convex) eyepiece. The earliest telescopes typically had convex objectives and concave eyepieces. The alternative proposed by Kepler had one major drawback; the resulting image would be upside-down. There was nothing in Kepler's work to suggest that his design would exhibit two important advantages over other early telescopes; it dramatically improved the field of view and that it allowed the use of measuring devices. This was to be discovered only by actually implementing the design [_3_] .
Why did Scheiner build an astronomical telescope when other scientists of his day seemed quite content with the Galilean telescope? The answer may require looking past Scheiner to his order, the Jesuits. Scheiner's unorthodoxy regarding telescope construction, use and theory was not out of place in the Jesuits. Another Jesuit of Scheiner's and Galileo's time, Niccolo Zucchi, demonstrated that a telescopic effect could be achieved using a combination of parabolic mirrors and lenses instead of just lenses. This crude reflecting telescope was built more than 50 years before Newton's famous telescope (see Reflecting on History).
The Jesuits' unorthodoxy also extended to how they used telescopes. Scheiner, like several other scientists of his day, was very interested in viewing sunspots. He decided against the dangerous approach of viewing these sunspots directly through a telescope. Instead he chose to view the image projected from the telescope. This was Scheiner's famous helioscope. Amazing as it might seem today, he also built a heavy camera-like device ( a camera obscura ) and positioned it behind his telescope. The image below, from a copy of the Rosa Ursina at Queen's University, shows how the telescope was used as part of a camera obscura. These innovations and those of another Jesuit, a Father Grienberger, resulted in the finest celestial images during Galileo's lifetime; the plates of the sunspots in Father Scheiner's Rosa Ursina.
Sometimes technological advances bring new problems and cause further technological breakthroughs. Scheiner's helioscope was heavier and more complex than other telescope configurations. His configuration of telescope and camera obscura was much heavier. It was necessary to develop a practical way of tracking celestial bodies in spite of the weight and complexity. Another Jesuit, Father Grienberger, developed a way of mounting telescopes, called an equatorial mount, which made it possible to track a star by altering position in only one axis. The other mounts required altering the telescope position in two axes. Even today, this mount is considered superior for any serious amateur astronomer and a must for astro-photography. Newton considered Scheiner's work on optics important enough to obtain a personal copy for his library [_4_] .
The Jesuits also have a connection with the spread of telescope technology beyond Europe. The first telescope in North America was a gift presented by the Jesuits in 1646 to Jean Bourdon, an engineer in New France (modern day Quebec) [_5_] . The first telescope in China was brought there by Johannes Schreck, another Jesuit, in 1621 (his trip from Europe started in 1618) [_6_] . The Jesuit Jean Richaud is wrongly thought to be the first to use telescopes for astronomical purposes in India. That honour goes to Jeremiah Shakerley (in 1651). Regardless, the contributions to astronomy from his early use of the telescope are notable. These include observations of a comet and the discovery that the bright star in Alpha Centauri was actually a double star [_7_] . The first telescope in the American colonies was thought to have arrived in the 1660's and the first telescope in the New World was probably brought over by Portugese mariners in 1614 (a telescope was mentioned in records of the battle of Guaxanduba, Brazil).
Copyright Joseph Sant (2019).
Cite this page.
Sant, Joseph (2019).Jesuits and the Early Telescope:Scheiner and Grienberger. Retrieved from http://www.scientus.org/Jesuits-Telescope.html
<a href="http://www.scientus.org/Jesuits-Telescope.html">Jesuits and the Early Telescope:Scheiner and Grienberger</a>