Astronomical Images : Frontispiece to the Rudolphine Tables

Johannes Kepler

Astronomical Images

Tycho Brahe's dying wish in 1601 was for the completion of astronomical tables for Rudolph II. Johannes Kepler was entrusted with this task, which allowed him access to Tycho's hitherto jealously guarded observations. It was completed in 1624 and after protracted negotiations with Tycho's heirs, the imperial treasury and printers, the Rudolphine Tables were finally published in 1627 at Ulm, dedicated to the then Emperor Ferdinand II (Rudolph II had died in 1612). The Tables were far more accurate than their predecessors, the Alphonsine and the Prutenic Tables. The margin of error stayed within ten seconds compared to up to five degrees with earlier tables. Instead of providing a sequence of planetary positions for specified days (which Kepler did in his Ephemerides, 1617, 1618, 1619, 1630), the Tables were set up to allow calculations of planetary positions for any time in the past or future. The precise geocentric positions had to be worked out from combining the heliocentric positions of the planets and the Earth that were calculated separately. Logarithms were used to facilitate calculation. Thus, although Tycho wished the tables to be based on his own system, it is clear from the way Kepler set up the tabulations that they were based on his own heliocentric system with elliptical planetary orbits. Early in 1627 Kepler submitted to Tycho's heirs a sketch for the frontispiece of the Tables, probably by his friend, the mathematician and Hebraist Wilhelm Schickard. They objected to the portrayal of Tycho, insisting that he be shown in a full-length fur robe with his medal, the Order of the Elephant. They also demanded an explanation of the image. In the frontispiece, engraved by Georg Celer of Nuremberg, Tycho is duly clad in an ermine robe and wearing his medal. The accompanying poem by Johann Baptist Hebenstreit (former rector of the Ulm Gymnasium), 'An idyll on the Keplerian star-spangled tower, showing depicted the birth and progress of astronomy up to our age and the quite new, long-desired and incomparable work of the Tables', provides the required description. The picture is of the temple of Urania, the muse of astronomy. Tycho Brahe takes centre stage, proudly pointing out his cosmological model shown on the ceiling (the Earth in the centre of the Universe with the Sun orbiting around Earth, but all the other planets orbiting around the Sun) to the seated Copernicus. The title of the book, Rudolphine Tables, hangs down from that cosmological model, possibly an allusion to Tycho's wish that the tables be based on his system. At Tycho's elbow is his book on planetary theories, the Progymnasmata. Tycho is leaning on an elegant Corinthian column, complete with an achanthus-leaf capital, which proudly displays his instruments, the quadrant and the sextant that perfected observations. The columns that support the temple symbolize by their form and condition the state of astronomical observation through history. The starry heaven is depicted on the floor of the base because it is the foundation on which the observations (columns) are built. Copernicus's column is of a much simpler form, carrying a Jacob's staff and the parallactic ruler which induced some careless errors in Copernicus's observations. On the column rest also the observations of Regiomontanus and Walther which aided Copernicus's work. The firm, but less elegant columns made of bricks with plenty of cracks flank Tycho and Copernicus and signify the achievements (from left to right) of Aratus, Hipparchus, Ptolemy and Meton. Aratus (4th c. BC) wrote a poem entitled the Phaenomena which explained the configuration of the heavens and their movements; his column sports an armillary sphere. Hipparchus improved on Aratus with a sphere of fixed stars and a catalogue of them. Ptolemy is depicted with an astrolabe, drawing a diagram. Part of the Greek title of the Almagest is visible and the diagram on the table in front of him shows Ptolemy's theorem (if a quadrilateral is inscribed in a circle, then the sum of the products of its two pairs of opposite sides is equal to the product of its diagonals). Meton's column carries a dial, showing the nineteen-year Metonic cycle after which the lunar phases recur on the same date. At the back, there are two columns made of tree trunks, with stumps, implying the absence of instruments to render them into more elegant shapes. In front of these columns stands a Chaldaean astronomer, trying to gauge the angular distance of planets using his fingers. On top of the roof of the Temple are six goddesses, signifying important elements of Kepler's astronomy. From left to right, they are optics (the shining head of the goddess is creating a shadow of a globe), the telescope, logarithms (holding in her hands rods of the ratio of one to two, and the number around her head showing the Keplerian natural logarithm of 1/2: 0.6931472), geometry (with a compass, square-ruler and a diagram of an ellipse), 'stathmica', namely the laws of the lever and balance (holding a balance, with the Sun at the fulcrum and a star at the end of the longer arm, an allusion to the slowing of a planet's motion as the magnetic force of the Sun decreases with increasing distance), and magnetics (holding a lodestone and compass). At the summit of the temple is the imperial eagle with his sceptre, showering a few gold coins down to the astronomers. Tycho's island of Hven is depicted in the centre panel of the base. To its left is a portrait of Kepler, with a miniature of the roof of the temple and a list of his books. To the right are two plaques illustrating the printing of the Tables. The nearer plaque shows, on the right, a press-man inking the exposed type lying on the platen. The press-man on the left has raised the frisket with his right hand and is now removing the printed sheet which he will pass to his left hand to place on the pile of printed sheets under the bed of the press, and replace it with a new sheet ready to be printed. The further plaque shows a compositor setting type.