Astronomical Images : Methods of observing sunspots

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. The quotation at the top is from Pliny the Elder's Naturalis historia II.112, where Eratosthenes's estimate of the circumference of Earth is described as 'an audacious venture, but achieved by such subtle reasoning that one is ashamed to be sceptical.' Inside the roundel is shown a terrace near a shore with two obelisks in the middle. At the bottom is a view of the interior of a room with astrolabes and a quadrant hanging on the wall. Three figures may be identified as Jesuits from their distinctive birettas. One is at the foot of the obelisk measuring the position of the reflected sunspot against a plumb line (at M) with a compass, and two inside a room, one measuring the position of the sunspots and the other transferring it onto paper. The Christogram 'IHS' adopted by the Jesuits as their emblem, may be seen at the top of one of the obelisks, and the rose of the Orsini family may be found on the edge of the roundel and elsewhere. On the side of a stool on which a telescope and sundial rest, is the signature of the engraver, Daniel Widman. This plate illustrates seven methods of observing sunspots: 1) the simplest and most natural way of observation is to let the Sun (at F) shine through a bare opening of a ball (at G) into a dark place where a paper is held perpendicularly and on which a figure is formed (at H). 2) another simple form of observation is to let the Sun (at Q) shine through a convex glass (at R) onto a chart (at S). 3) the simplest and most natural way of observation is with the naked eye (at P) when the Sun is at the horizon (at I). 4) observation of the Sun (at E) through a helioscope (at D). 5) observation of the Sun (at B) behind a cloud (at C) through a telescope (at A). 6) observation of the Sun (at I) by a reflection (at LN) by a plane mirror (at K). This is a method that Scheiner initially used at Ingolstadt. 7) observation of the Sun where its ray (V) through a helioscopic tube (at X) is projected onto paper in the circle Y contained in the perimeter cfdg. This method is described as 'the most excellent, the most secure and the easiest' method of observation which Scheiner used at Ingolstadt from 1612, as well as at Rome.