1742 Doppelmayr Celestial Chart of the Orbits of Mercury and Venus

This is the 1742 Atlas Novus Coelestis edition of J. G. Doppelmayr's chart of the orbits of Venus, Mercury, and the Sun following the theory of planetary motion proposed by Tycho Brahe. That 16th-century Danish astronomer's efforts to explain the confusing behavior of the planets while retaining an orderly vision of the cosmos led to the production of many fascinating images, this not least among them. Doppelmayr presented Tycho Brahe's model here in contrast to the Copernican model, declaring the simplicity of the latter to exemplify its superiority over the contortions made necessary by the former.

A Compromise Cosmology

Doppelmayr, a mathematician and astronomer, was above all an educator. As such, his star charts and diagrams of the solar system described the whole progress of scholarly study of the heavens. It is into that progress in which the present image fits. His charts of the solar system compared the dominant models of previous centuries: the Earth-centric model of second century astronomer Claudius Ptolemy, the challenging heliocentric view of Nicolaus Copernicus (February 19, 1473 - May 24, 1543), and the compromise view of Tycho Brahe (December 14, 1546 - October 24, 1601). Brahe's model proposed a geocentric solar system in which the Sun and Moon orbited Earth, but that the other planets orbited the Sun (a model that safely rejected heliocentrism, while agreeing better with Copernicus' observations). All these early models of the solar system shared a flaw, however, in that they presumed the motions of the sun and the planets to fall within perfect circles. Astronomers, then, were puzzled by the phenomenon of retrograde motion, in which the relative position of Earth-bound observers and a given planet would result in a planet seeming to change direction in its path across the heavens, move backwards for a time, and then resume its 'forward' motion. For Tycho this phenomenon as exemplified by Venus and Mercury's orbits around the Sun, which in turn orbited Earth. One happy result of this head-scratching proposition is the necessity of producing diagrams, such as this one, to illustrate it. Doppelmayr places Earth and part of the lunar orbit in the center of the chart. The sun is given a circular orbit around the Earth. The paths of Venus and Mercury are then shown in a looping, slightly mad trajectory around the Earth. (Smaller diagrams - Fig I and Fig II - clarify that the two inner planets actually moved in neat circular solar orbits, resulting in their apparently strange path around Earth.) Doppelmayr's chart was not merely a restatement of Tycho's theories: the positions marked on the chart were based on his own observations of the planets in 1712 and 1713, laid out in the diagrams according to Tycho's principles. The tracks of the sun and planets are marked with their respective dates, showing their changing position in time.

A Playful Engraving

The chart isn't all business. At the center of the engraving, Venus and Mercury are depicted as children playing on swings, pushed in turn by the sun. Ellington was right: the image is an allusion to their reversals in relation to the sun in their respective orbits. In the upper hemisphere of the main diagram is a Latin excerpt from Ovid's recounting of the ride of Phaethon - the disastrous affair of the young, mortal son of Helios, the sun god, insisting on being allowed to drive his father's chariot. The passage in question takes place after Helios' horses, by then having predictably wrested control from the feckless Phaethon, describe a wild and decidedly unpredictable trajectory through the skies, setting alight mountains and forests alike. The application of the passage here is an allusion to the apparently crazed path taken by the wandering planets (albeit exaggerated, neither Venus nor Mercury having set fire to anything on Earth more dangerous than an imagination.)

Publication History and Census

This plate was engraved by Johann Baptist Homann, from the drawings of Johann Gabriele Doppelmayr. In its present state, it was included as plate 9 in the latter's 1742Atlas Novus Coelestis. It was completed no later than 1716 and was from that time included in Homann's atlases. Atlas editions of the chart lack the plate number and in and around 1737 the Imperial Privilege was added. The privilege was burnished out prior to the publication of the chart in the Doppelmayr atlas. Thus, this is the third of three states of the chart that we have identified. The Doppelmayr atlas and its individual sheets are well-represented in institutional collections and reach the market from time to time.