Academic journal article Journal of the History of Ideas

Shadows of Instruction: Optics and Classical Authorities in Kepler's Somnium

Academic journal article Journal of the History of Ideas

Shadows of Instruction: Optics and Classical Authorities in Kepler's Somnium

Article excerpt

Johannes Kepler's posthumous work Somnium relates a strange dream that culminates in a detailed picture of the way the heavens appear to a lunar observer. This knowledge is revealed to the dream's protagonist by a daemon that teaches and explains the main tenets of the lunar astronomy. This daemonic instructor, however, presents itself not as a source of illumination and clarity, but as a shadowy creature, "For as a group we [the daemons] inhabit the earth's shadows.... Up there [on the moon] we quickly withdraw into caves and dark places.... As soon as a spot begins to be free from the sun, we close ranks and move out into the shadows."1

Instead of the enlightened Platonic teacher, the reader encounters shady daemons, who live in dark caves, where they are granted leisure "to exercise our minds in accordance with our inclination." The reader might associate this curious characteristic with the general occult ambience of the dream, and might relate it to the protagonist's mother-witch. Kepler, however, explains that this fascination with shadows and darkness is directly related to scientific observation and knowledge, "The allegory compares the journey through the shadow to the observation of eclipse... the time spent in the caves, to continuous speculation based on observation of the eclipse." Kepler proceeds to his own personal experience. "In Prague I had a residence in which no spot was more suitable for observing the sun's diameter than the underground beer cellar. From the floor of the cellar I used to aim an astronomical tube, described in my Optics, through an opening at the top toward the noonday sun on the days of the solictice."2 The reader is transported into the dark-room, with its technologies of observation as a place of true and clear knowledge. Shadows and darkness are transformed from obstacles into vehicles of knowledge; the daemon and its shadowy world are the true teachers of astronomy: "However, to the extent that... the daemon stands for the science of astronomy, there is seriousness in the assertion that for the mind there is no passage to the moon except through the earth's shadow and the other things which depends on it."3

This change in the value of shadows in relation to knowledge already took place in Kepler's 1604 magisterial work on optics. In his preface Kepler ponders the origins of astronomy. Following Pliny, he posits the eclipsed luminaries as the trigger for human curiosity that led them out of a world of ignorance.

For the most noble and ancient part of astronomy is the eclipse of the sun and the moon, a subject that, as Pliny says, is in the entire study of nature the most wondrous, and most like a portent.... For this theater of the world is so ordered that there exist in it suitable signs by which human minds, likenesses of God, are not only invited to study the divine works ... but also are assisted in inquiring more deeply. For I implore you what is the cause, if not this, for nature's playing such games in the sun's and the moon's bodies, by which not only humans ... are turned to wonder and stupefaction, so long as they are ignorant of the causes, but even the quadruped, by Pliny's testimony, commonly take fright?4

The dramatic encounter of the earth, the moon and the sun was the game nature offered the human observers in order to arouse their curiosity. Kepler further claims that it is this distortion in the celestial order that, leads humans in their quest for knowledge: "It is believed rightly that all of astronomy is born from this obscurity of the luminaries. Just as these darknesses may be the eyes of the astronomers, these defects may be a rich source of doctrines these 'stains' may illustrate the most precise pictures on the mortal mind. O most excelled and commendable sign for all the nations about the glory of the shadows."5

In the ensuing optical treatise, Kepler establishes shadows and their measurement as a solid basis for scientific observation. …

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