Christoph Scheiner (1575–1650)

The Jesuit astronomer Christoph Scheiner was born on July 25, 1575. He joined the Jesuit order in 1595, and started his studies in 1601 at Ingolstadt where he later taught mathematics from 1610 to 1616.He moved to Innsbruck in 1616, was in Rome from 1624 to 1633, and died in Niesse on June 18, 1650. The above portrait is from the Stadt Müseum Ingolstadt.

Christoph Scheiner  image
Portrait of Christoph Scheiner (1575–1650).
Credit: Wikipedia.

The controversy between Scheiner and Galileo over priority in the discovery of sunspots was an important factor (though not the only one) responsible for the degradation in the relationship between Galileo and Roman members the Jesuit Order. By his own account Scheiner began observing sunspots in March or April 1611,together with his then assistant J.B. Cysat. The first published account of his observations are his "Three Letters on Sunspots" (Tres epistolae de maculis solaribus), dated November 11, 1611, addressed to Augsburg magistrate Mark Wesler (1558–1614) and published in Augsburg in January 1612. These were followed by three more letters in September 1612, again published via Wesler. Scheiner was required by his ecclesiastic superiors to write under the pseudonym "Appelles", to avoid possible embarrassment to the Jesuit order in the event that his findings were to prove spurious.

Scheiner's original opinion was that sunspots were small planets closely orbiting the Sun, a position convincingly refuted by Galileo in his own 1632 "Letters on Sunspots". Unlike Galileo, Scheiner pursued sunspot observations on a continuous basis for more than 15 years. In the course of doing so he devised techniques that greatly improved the accuracy of observed sunspot positions, and "designed specialized solar observing instruments". Results of his observations were published in 1630 in his "Rosa Ursina", a book four years in the making that opened with biting attack on Galileo. Galileo defended this attack in his famous publication, "Dialogue".

Scheiner's Sketches and Writings

Rosa Ursina

Frontispiece of Scheiner's Rosa Ursina
Frontispiece of Scheiner's "Rosa Ursina", published in Bracciano between 1626 and 1630 [1].

Scheiner's Rosa Ursina, partly as a backlash following Galileo's condemnation, the massive volume (780 pages) did not draw very positive reviews following its publication, nor did it go down too well in history, largely because of the various vociferous attacks on Galileo scattered throughout Book I. The book was not without merit, however. In it Scheiner uses his observations of sunspot paths across the solar disk to convincingly demonstrate that the Sun's rotation axis is inclined with respect to the Earth's orbital plane. This observation was taken up as his own by Galileo in his Dialogues as a further argument for the heliocentric hypothesis, which was to further provoke Scheiner into accusations of plagiarism. In addition, the book has proven very useful as a store of sunspot data for to the period immediately preceding the Maunder minimum. Scheiner's later book, "Prodromus pro Sole Mobile", a rabid criticism of Galileo's 1632 Dialogues, was withheld from publication during Scheiner's lifetime, apparently because it was deemed overly distasteful by his ecclesiastic superiors.

The inclination of the Sun's rotation axis

sunspot drawings in Scheiner's Rosa Ursina
Drawing shows apparent paths of sunspots across the solar disk, for two sets of observations taken six months apart.

One of a great many sunspot drawings in Scheiner's "Rosa Ursina", reproduced from The history of the discovery of the solar spots, in Popular Astronomy, 24, W.M. Mitchell, 1916. Based on such observations, Scheiner correctly concluded that the Sun's equatorial plane is inclined by 7° with respect to the ecliptic. This observation was taken up as his own by Galileo in his "Dialogue concerning the two chief world systems" as a further argument for the heliocentric hypothesis, which was to further provoke Scheiner into accusations of plagiarism.


Scheiner's helioscope

Helioscope
Scheiner's helioscope, after a drawing in Scheiner's "Rosa Ursina".

While Galileo largely abandoned systematic sunspot observations following the publication of his "Three letters on Solar Spots", Scheiner devoted himself fully to sunspot observations. He improved onthe projection method of Galileo and Castelli by designing a specialized telescopic solar projection instrument, which he called heliotropii telioscopici (helioscope being a rough contracted translation). This represents the earliest known equatorially mounted instrument.

Bibliography:
[1] Mitchell, W.M. 1916, The history of the discovery of the solar spots, in Popular Astronomy, 24, 22-ff.