Astronomical Images : Comparison between the eye and the optical tube

Christoph Scheiner

Astronomical Images

Christoph Scheiner (1573-1650) joined the Society of Jesus in 1595. He studied at the University of Ingolstadt, where he was appointed Professor of Hebrew and Mathematics from 1610. He is also known for having invented the pantograph and for establishing the retina as the seat of vision. Scheiner began to make astronomical observations using a telescope from 1611 and noticed specks on the Sun. He believed them to be planets around the Sun, and published his views anonymously, calling himself 'Apelles hiding behind the painting' for fear of bringing the Jesuit order into disrepute. Three Letters on Solar Spots (1612) were published by Marc Welser to whom Scheiner had written about his discoveries. Galileo correctly identified the author as a Jesuit and wrote a refutation addressed to Welser, published as History and Demonstrations about Sunspots and their Properties by the Lincean Academy in Rome in 1613. Galileo further criticized Scheiner in The Assayer. Scheiner's astronomical research, punctuated by service at the court of Archduke Maximilian at Innsbruck and as confessor to Archduke Charles, the bishop of Neisse, culminated in Rosa Ursina sive Sol (The Rose of the Orsini, or the Sun) in which he defended his position against Galileo and showed that the inclination of the axis of the rotation of the sunspots to the plane of the ecliptic was 7Ë?30'. Rosa Ursina sive Sol was a large tome richly illustrated with engravings, and therefore costly. Scheiner originally sought the support of Cardinal Alessandro Orsini (1592-1626), who was close to the Jesuits, and after Alessandro's death, that of his brother, Paolo Giordano II, Duke of Bracciano. Rosa Ursina sive Sol was thus published at Bracciano, though over several years (1626-30) due to financial difficulties. The book, starting with its title, is replete with references to the Orsini family whose heraldry included the rose and the bear (orsus = ursus = bear). Given the strained relations with Paolo Giordano II, who was unwilling to pay for the book, these references to the Orsini family quickly became obsolete. Scheiner had determined in his Oculus (1619) that the retina was the location of the image formed in the eye. This table shows a 'Comparison between art and nature, between the tube and the eye in forming solar images'. It is a skilful visual argument to show that the same optical principles govern optical tubes and the eye with or without additional concave or convex lenses by juxtaposing the two. This point was important for Scheiner in order to refute those who claimed that the sunspots were the by-products of a defective instrument or human imagination.