Astronomy and the Archduke: Unpublished Letters on SN1604 by Brengger,Coignet,and Kepler in the Archives of Albert VII of Austria

Introduction

At the turn of the sixteenth to the seventeenth century, the Seventeen Provinces was a country that had been ravaged by three decades of civil war. Yet, no end to the hostilities seemed imminent. The civil war had turned into a war between Northern rebellious provinces and the reconquered Spanish Southern provinces.

Since 1596, the Southern Netherlands was ruled by Archduke Albert VII of Austria (1559–1621), ³ as governor. In 1597, he married Infante Isabella Clara Eugenia (1566–1633). ⁴ The Archdukes, as they would become known, received sovereignty over the Seventeen Provinces as a dowry. In practice, this meant they ruled the Southern Netherlands. ⁵

Politically, Albert would pursue a double agenda, opposing the United Provinces with arms on one hand, and signalling to them and to France and England his desire to conclude a peace on the other. ⁶ One of his strategic aims would be to clear the left bank of the Scheldt of protestant strongholds.

On 5 July 1601, Albert’s troops laid siege to Ostend, the last of these strongholds in the Southern Netherlands. The town, however, could be provisioned by sea which weakened the aim of a siege: starving the garrison and the population into submission. Ostend finally fell after a siege lasting more than 3 years on 22 September 1604. ⁷

The war in the Low Countries dragged on until, in 1609, the war-weary parties concluded the Twelve Years’ Truce. In the south, the truce was the period in which the economic recovery gained momentum. Fiscal policies were relaxed, and cultural expenditure rose to levels never seen before. New and magnificent churches and convents were built on a scale unparalleled outside of Italy. This was the period in which the image of the Archdukes as fair and just rulers of an economically prosperous country and as patrons of the arts was forged.

Michiel Coignet

Michiel Coignet (1549–1623) ⁸ followed in his father’s footsteps as a scientific instrument maker. His professional career began in 1568, when he entered the schoolmaster’s guild. His first signed astrolabe dates back to 1572. In that same year, he became an official winegauger of the City of Antwerp. He would keep this position until 1596 when he resigned because he had become Court mathematician. As such, he inspected many fortifications near Antwerp and in the Land van Waas, on the Scheldt’s left bank. ⁹ Apparently, Michiel Coignet’s advice was sought at the siege of Hulst (1596), the first of Albert’s many sieges. ¹⁰

On 22 October 1596, Coignet received 600 Flemish pounds to have the figures of a mathematical manuscript engraved. The gift was deemed necessary by the Archdukes “to revive the anemic science of mathematics.” ¹¹ He would receive other gifts by the Archdukes on an irregular basis. For instance, on 13 April 1604, he was awarded 1000 Flemish pounds by the Archdukes for his services as a cosmographer, but the payment of this grant was postponed until the following year. ¹²

Coignet produced the most beautiful astrolabe ever to leave his workshop in the 1610s. The astrolabe bears a crown on the rete. Instead of the usual tulip-shaped rete of Flemish and Dutch astrolabes, here we find the letters A and Y artistically intertwined. ¹³ These letters are the initials of Albert and Isabella. It is not clear whether the astrolabe was commissioned by or presented to the Archdukes.

In 1573, Coignet’s book Cent Questions Ingénieuses, in which his interest in astronomy and spherical trigonometry becomes clear, was published as an appendix to his adaptation of Valentin Mennher’s (1521–1570) Livre d’Arithmétique. In Cent Questions Ingénieuses, problems are proposed to determine one’s geographical position given a number of observations and to the construction of sundials. These topics also appear in his manuscripts on the sector. ¹⁴

In Nieuwe Onderwijsinghe (1580), his book on navigation, Coignet is more explicit. Here he claims to be able to calculate new planetary tables and announces that he will publish his ideas in a book Theoricas Planetarum, ¹⁵ which, as far as we know, was never published. For more than 20 years, he maintained that a publication was imminent. ¹⁶

Coignet was involved in publishing atlases from the 1590s onwards. In these, his introduction invariably describes the Ptolemaic world view: Earth, a sphere consisting of water and land embraced by air, is the centre of the universe. In the mathematical introduction to the 1612 edition of Ortelius’ Theatrum however, he refers to the comets of 1572 and 1600, as well as the supernova of 1604, to support the argument that Aristotle’s notion of immutable superlunar heavens was incorrect. He does not digress on this topic any further however. ¹⁷

An indication of Coignet’s own conception of the universe comes from an unusual source, namely, a dedication he wrote in Gillis Anselmo’s (1536–1611) Liber Amicorum of 12 November 1601. ¹⁸

In this liber, Coignet drew a figure representing the Tychonic system, to which he added the comment, Systema Vranicum, iuxta quod noue Caelestum Orbiu hypotheses, M. Coignéti phenomenis congruentes ¹⁹ excogitate sunt (This is the system of the heavens, leading to the new hypotheses of the heavenly orbs, proposed by Michiel Coignet, which ties in with the observed phenomena). Although Coignet claims this geo-heliocentric system to be his own, it is nothing else than Tycho Brahe’s model. ²⁰

It would have been expedient to adhere to Tycho’s system in courtly surroundings where the ideas of the Counter-Reformation prevailed.

The appearance of comets and other unexpected celestial phenomena usually caused a stream of publications. This was certainly the case in 1604, when a supernova appeared in the skies. The phenomenon also drew the attention of scientists, such as Michiel Coignet, who, together with Paul Arnerio, reportedly wrote a book on it titled Discorso sopra la nuova Stella (Padua, 1605). ²¹ We know of no copy of the book, but according to Alberi, the authors assert that the phenomenon took place outside the sphere of the Moon.

Johannes Brengger

The most complete biography of Johannes Brengger up to now still is the hard to find 1914 book by Otto Sommer, ²² on which much of the following paragraph is based.

Johannes Georg Brengger was the son of a prominent Augsburger family. ²³ The exact date of his birth is not known, but the fact that he converted to Protestantism in 1629 at the age of 70 indicates that he must have been born no later than 1559. ²⁴ He attended university at different cities: Tübingen, Padua, and Basel. At the University of Basel, he received his doctorate in 1588. ²⁵ Nearly 2 years later, he was admitted to the College of Physicians at Augsburg. ²⁶ He married that same year.

In 1594, he became town physician of Kaufbeuren, which he would remain until 1629. ²⁷ In 1629, he returned to Augsburg ²⁸ to become Dean of the College of Physicians. During this period, Augsburg suffered a pestilence epidemic, to which Brengger’s son Matthias (d. 1628), a physician as well, succumbed. No trace of Johann can be found after 1629, indicating he suffered the same fate. ²⁹

At least from 1592 onwards, Brengger made astronomical observations. ³⁰ In 1599, Brengger wrote a letter to the Bavarian chancellor Herwart von Hohenburg (1553–1622), ³¹ the first known letter in his own hand. At that time, von Hohenburg was one of the most prolific correspondents of Kepler. In his answer, von Hohenburg asks about Brengger’s views on Earth magnetism. ³²

In 1604, Brengger received a, now lost, letter from Kepler to which he responded on 23 December. Both men entered into a correspondence which would last at least until May 1608. ³³

Among Brengger’s other correspondents, ³⁴ we find Johann Bayer (1572–1625), ³⁵ Helisaeus Roeslin (1545–1616), ³⁶ Willebrord Snell (1580–1626), ³⁷ Johannes Faulhaber (1580 1635), ³⁸ and Joachim Jungius (1587–1657). ³⁹

Brengger was very interested in the appearance of the New Star of 1604. As to the determination of the time of its appearance, he was misled by his astrological beliefs. He did not observe the first appearance but conjectured it in relation to the conjunction of Mars and Jupiter. ⁴⁰ He made numerous measurements of the New Star, which were later used by Kepler in his De Stella Nova. His remarks on brightness and colour give credit to the accuracy of his measurements. Yet he himself complains about the inaccuracies in his observations, for which he blames himself as an observer.

In his letter to Kepler, ⁴¹ Brengger gives two possible ecliptic coordinates ⁴² : longitude 17° 34 ½′, latitude 1° 53′N and longitude 17° 34 ½′, latitude 1° 54′. Except for the diurnal motion, Brengger found no movement and therefore was inclined to regard the phenomenon as a fixed star. He thought the phenomenon was smaller than the one seen in 1572, and he also thought it scintillated more. The first observations nevertheless indicated that the star of 1604 was larger than that of 1572. Moreover, Brengger indicated that the colour of the star had changed since its first appearance.

He was also concerned with the question of how the New Star was created. He does not share Kepler’s view that it was formed by the “facultas formatrix” of the “air of the sky.” Indeed, he rejects his views using Aristotelean–Ptolemaic philosophy. He is however broad-minded. He himself hypothesizes that the star was formed by pre-existing galactic matter and that this is a phase in cosmogenic development. ⁴³

When a comet appeared in the Fall of 1607, Brengger again made accurate observations. This is the comet which, from 1682 onwards, would be known as Halley’s Comet. ⁴⁴ He thought that the comet, and the other comets he had observed, was superlunary phenomena. His attempts to determine the parallax of the comet indicates that he saw them as celestial bodies; he was however defeated by the distance to the object and the (in)accuracy of his instruments. As to the nature of comets, he thinks they are formed by the amalgamation of a fine primaeval matter, which it afterwards again loses.

At that time, Kepler had finished his studies on Mars, his manuscript was with the printer Vögelin in Heidelberg, but Emperor Rudolf (1552–1612) had not given his consent to publish. Kepler informed Brengger of this adding that the book would also contain his philosophy of the structure of the Universe. He asked Brengger to read through the proofs. ⁴⁵ It would appear only in 1609 as Astronomia Nova, the book containing Kepler’s first and second law.

From his correspondence with Herwart von Hohenburg (1553–1622), it becomes clear that Brengger adhered to conventional astrology as practised in the later sixteenth century. Later he abandoned astrology altogether. ⁴⁶

Brengger made some important investigations into the nature of Earth magnetism. Again, from his letters to Herwart von Hohenburg, we know he tried to determine the position of the magnetic North Pole by theoretical considerations only. He had read Mercator’s work and in a similar manner, hypothesizing that there is a uniform distribution of the magnetic declination, he calculates this position. The fact that he obtains a different position than Mercator’s is attributed to errors in the observation of the declination. He therefore thought that determining longitude was possible, given ones latitude and magnetic declination. ⁴⁷ However, once he became familiar with Gilbert’s work, he understood the futility of trying to draw up tables and then rejected the existence of such a thing as a magnetic pole. ⁴⁸ Gilbert’s work would also lead Brengger to see magnetism as the force which brings order to the trajectories of the planets. ⁴⁹

The astronomical setting

During the Middle Ages, two more or less opposing worldviews existed: the philosophers’ and the mathematicians’ worldview. ⁵⁰ The philosopher’s cosmology largely drew its inspiration from Aristotle’s On the Heavens. In this book, Aristotle describes the universe in terms of motion and rest. The centre of the Universe is a spherical and immovable Earth. In the neighbourhood of Earth, bodies composed of the four elements can move either up or down depending on their natural inclination. This neighbourhood of Earth is the sublunar sphere, the only sphere in which change is possible. The other spheres, which carry the Moon, the Sun, the planets, and the firmament of fixed stars, are immutable. These spheres consist of a fifth element, unknown on Earth: ether. ⁵¹ The system was not as rigid as described here. It had absorbed Christian teachings and stoic philosophy and was able to accommodate certain new phenomena. ⁵²

Mathematicians were more down to Earth. They were less interested in the structure of the Universe than in being able to calculate the planetary positions. They would use Ptolemaic astronomy, with its epicycles, to create a clockwork universe. The sixteenth-century pinnacle of this endeavour was Copernicus’ work on the Revolutions of the Heavenly Spheres. ⁵³ In part, their work was also related to astrology, in its turn necessary in medicine. It is therefore no surprise that physicians, such as Gemma Frisius (1508–1555), were also mathematicians and astronomers cum astrologers. ⁵⁴

During the sixteenth century, observations of the night sky put the view of the immutability of the heavens into question. Calculations were beginning to show that comets were superlunary. In Hven, at his castle Uraniborg, Tycho Brahe (1546–1601) set up an observatory with instruments of a precision the world had never seen before. ⁵⁵ Tycho’s observations provided an answer to the gridlock cosmology had fallen into. In the hands of Johannes Kepler, his observations were the basis of a model which would shatter the philosophers’ and the mathematicians’ world view alike.

Comets and New Stars were phenomena which lent support to a new cosmology, although acceptance of it did not come overnight. The absence of a parallax put both New Stars and comets in the superlunary spheres. But, as the comet of 1577 showed, the Aristotelean model showed itself resilient. Divine intervention and the introduction of intermediate regions rendered the acceptance of a heliocentric theory unnecessary – as yet. ⁵⁶ Comets and New Stars appearing in the next few decades would remain to raise doubts about the traditional worldviews and would turn out to be nails in their coffin (Figure 1).

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Figure 1.

The Erfgoedbibliotheek Hendrik Conscience in Antwerp is the proud owner of two huge globes made by Joan Blaeu (1596–1673), a terrestrial and a celestial globe. The terrestrial globe was made c. 1645. Dating of the celestial globe is less certain; star positions were based on the catalogue of Tycho Brahe and, for southern latitudes, of Frederik de Houtman (1571–1627). Both the novas of 1572 and 1604 are indicated on the globe. The globe also carries a little portrait of Tycho and a text cartouche around it. ⁵⁷ © Erfgoedbibliotheek Hendrik Conscience, Antwerpen.

The New Stars

In some of the letters, SN1604 is compared to SN1572, also called Tycho’s supernova. SN 1572 appeared in the sky between 3 and 6 November 1572 in the circumpolar constellation of Cassiopeia. It appears to have reached a maximum brightness by the middle of November. This brightness was reported as surpassing that of Jupiter, but fainter than Venus. ⁵⁸

The radio source 3C10 is identified as the remnant of SN1572. It is very weak in the optical spectrum and is also a weak X-ray source.

Tycho measured the angular separation of SN1572 to nine reference stars in the constellation of Cassiopeia and to the Pole Star. Other measurements were made by Thomas Digges (1546–1595), ⁵⁹ Michael Maestlin (1550–1631), ⁶⁰ Jeronimo Muñoz (c. 1520–1591), ⁶¹ and Tadeáš Hájek (1525–1600). ⁶² We know Digges used a cross staff ⁶³ for his measurements, while Tycho Brahe used his recently completed sextant, graduated in minutes of arc. ⁶⁴ From their measurements, Tycho, Maestlin, and Digges concluded that there was no visible parallax and therefore SN1572 was a superlunary phenomenon among the sphere of the fixed stars (Figures 2 and 3).

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Figure 2.

Cassiopeia, with an indication of SN1572, in a damaged part of Blaeu’s globe. The text reads, “Nova et admirabilis stella anno 1572 visa quae per totos sexdecim menses luxit de qua leg[o?] Tychonem.” (The new and admirable star which appeared in 1572 which could be seen for 16 months, of which I read in (the book of) Tycho). © Erfgoedbibliotheek Hendrik Conscience, Antwerpen.

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Figure 3.

This composite image of the Tycho supernova remnant combines infrared and X-ray observations obtained with NASA’s Spitzer and Chandra space observatories, respectively, and the Calar Alto observatory, Spain. It shows the scene more than four centuries after the brilliant star explosion witnessed by Tycho Brahe and other astronomers of that era.

The three decades separating 1572 to 1604 saw the appearance of five comets (1577, 1580, 1582, 1585, 1596) and two variable stars: Mira Ceti and P Cygni. ⁶⁵

David Fabricius (1564–1617) ⁶⁶ discovered a new star which was later designated Mira Ceti or o(micron) Ceti. ο Ceti is actually a binary stellar system, consisting of a variable red giant (Mira A) along with a white dwarf companion (Mira B). It was first observed by Fabricius on 3 August 1596, by October it had faded from view. Fabricius saw the star again on 16 February 1609. ⁶⁷ It would turn out that Mira Ceti is a variable star with a period of about 332 days (Figure 4).

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Figure 4.

Cetus on Blaeu’s globe. © Erfgoedbibliotheek Hendrik Conscience, Antwerpen.

In his letters, Coignet mentions a new star which appeared in 1600 in the constellation of Cygnus, also known as the Northern Cross. Unlike the new stars of 1572 and 1604, it was not a supernova. Next to several bright stars, such as Deneb (α Cygni), Cygnus is also the home to several variable stars. One of these is P Cygni, a hypergiant luminous blue variable, one of the most luminous stars in the Milky Way, located some 5000 light years from Earth. ⁶⁸ It seems to have been first observed by Willem Jansz. Blaeu (1571–1638) on 18 August 1600, when it brightened from obscure to third magnitude (Figure 5). ⁶⁹ From 1606 onwards, it began to fade, becoming invisible to the naked eye in 1626. During the seventeenth century, it had several flare ups. Today it is a 4.8 magnitude star of irregular variability. It has been suggested that P Cygni has a companion star in a binary system. ⁷⁰

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Figure 5.

Cygnus or the Swan in a damaged part of Blaeu’s globe. The text reads, “Nova in Cygno stella, anno 1600 Augusti 18 primum a me summa cum admiration obseruata est, et initio quidem magnitudinis tertiae cujus locum è distantia a lucida Lyrae et cauda Cygni deprehendi in 16. Grad. 15. Min. cum latitudine Bor. 55.50. Quae stella etiamnunc in eadem sede defixa, eandem quidem a dictis distantiam obtinet, fulgore tamen adeo imminuta ut jam quintae magnitudinis syderibus duntaxat annumeranda videatur.” (The New Star in the Swan, which I, with great admiration, first observed on 18 August 1600 and which at the first observation was of the third magnitude. I have determined her position from the [angular] distance to the brightest [star] of Lyrae ⁷¹ and to the [star] in the tail of the Swan ⁷² at longitude 16° 15′ in Aquarius and latitude 55° 50′ north. This star is has remained invariably in the same position and still has the same [angular] distances to the aforementioned [stars] but with a brightness which has diminished to that extent that it seems that it has to be counted among the stars of the fifth magnitude). © Erfgoedbibliotheek Hendrik Conscience, Antwerpen.

In 1604, observers like Coignet experienced what no naked-eye astronomer before them or since them has seen: a second supernova during their lifetime. ⁷³ The first sighting of a New Star within the constellation Ophiuchus was on 9 October 1604 by two Italian observers, one of whom reported it to Christopher Clavius S.J. (1538–1612). ⁷⁴ SN1604 appeared a mere 3° northwest of Mars and Jupiter. Due to a predicted conjunction of Mars and Jupiter, this part of the sky was kept under close scrutiny at the time. It therefore comes as no surprise that the supernova was seen almost as soon as it appeared, despite the fact that with a southerly declination of –21° and a longitude of 58° E, it was in close proximity to the Sun. It reached its maximum brightness around 1 November (see Figures 6–7). ⁷⁵

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Figure 6.

Ophiuchus or the Serpent bearer with an indication of SN1604 on Blaeu’s globe. © Erfgoedbibliotheek Hendrik Conscience, Antwerpen.

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Figure 7.

Detail of the leg of Ophiuchus or the Serpent bearer with an indication of SN1604 on Blaeu’s globe. The text reads, “Anno 1604 mense Octobri nova Stella in sese videndam exhibuit; quae Iovem fulgore et radiorum splendido jubare non aequaret et modo, sed etiam superaret cujus locum initio è distantijs a lucida Vulturis, capite Ophiuchi et corde Scorpij deprehendi in 17.4 lat.Bor. 1.42 et in Sequentem annum 1605 perennavit, fulgorè tumen diminuto, ut sub finem ejus evanesceret, mutata latitudine, et simul longitudine, in consequentia signorum namq _ɀ 20. Augusti ejusdem anni 1605 deprehendi eam in 19.38 latitud. Bor. 1.9.” (During 1604, in the month of October, a New Star appeared in (the constellation of) Sagittarius, with a brightness and brilliant radiance which did not equal that of Jupiter but exceeded it. I initially determined her position from the (angular) distances to the bright (star in the) Vulture (the Eagle), ⁷⁹ the (star in the) head of the Serpent Bearer ⁸⁰ and (the star in) the heart of Scorpio, ⁸¹ at longitude 17° 4′ in Sagittarius and latitude 1° 42′ north. And it remained until the following year, 1605, but with diminishing brightness making her disappear by the end (of that year). The latitude, and the longitude as well, had changed relative to the signs (of the Zodiac). For I determined her (position) on 20 August of that same year 1605 at longitude 19° 38′ and latitude 1° 9′ north.) © Erfgoedbibliotheek Hendrik Conscience, Antwerpen.

A conjunction with the Sun made it temporarily invisible from 9 December onwards. It became observable to the naked eye again on 27 December, as observed by Korean observers. ⁷⁶ Kepler noticed the celestial body again on 3 January 1605. It was last sighted on 8 October 1605. Clark and Stephenson have drawn up a table of the brightness of SN1604, but give no data between 17 October 1604 and 3 January 1604. They drew a light curve based on European and Korean observation. Pilar Ruiz-Lapuente used their results to compare the luminosity of SN1604 with the predicted light curves of a Type Ia supernova (see Figures 8–9). ⁷⁷

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Figure 8.

Kepler’s supernova remnant: A view from Hubble Space Telescope in visible light.

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Figure 9.

Magnitude of SN1604 compared to supernovae Type IA models, taken from P. Ruiz-Lapuente, “The light curve and distance of the Kepler Supernova” (Note 77). The original caption reads, “Visual light curve of SN1604 around maximum light. The Korean records are indicated by filled circles and the European ones are indicated by open circles. The observations are compared with a normal SN Ia with stretch s = 0.9, with an overluminous and slow-declining with s = 1.2 SN Ia; and with an underluminous and fast-declining with s = 0.62 SN Ia.” Reproduced by permission of the AAS.

Currently, the remnant is designated G4.5 + 6.8 but is often referred to as Kepler’s SNR. The remnant is a limb-brightened SNR at radio and X-ray wavelengths. ⁷⁸

The letters

One problem facing sixteenth-century astronomers was determining a star’s longitude. ⁸² The vernal equinox is the zero point for measuring astronomical longitude. Since this is the intersection of the ecliptic and the equator, it is defined by the motion of the Sun. Using theoretical calculations, the Sun’s longitude can be determined for any given time. The angular distance between an ecliptic star and the Sun would therefore determine the star’s longitude. The problem is of course that a star and the Sun can never been seen at the same time. The problem can be overcome using the position of the Moon, for example, during an eclipse. Obviously, determining the longitude of a star is a long and tedious process. Therefore, the position of a star or a (new) celestial phenomenon, be it a comet or a supernova, was given relative to a few reference stars. In the letters published here, this is relative to stars in the constellation of Sagittarius.

Letter 1 and, as we will show, letter 2 are most probably copies of letters by Brengger. Comparison between handwriting of the letters in the Brussels archives and the ones in the Bayerische Staatsbibliothek ⁸³ shows that they were most probably not written by the same person. ⁸⁴

All relevant letters have been reproduced in Appendix 1. In this paragraph, we will put them into perspective. The letters can be found in the file Duitse Staatssecretarie 323 of the Belgian State Archives (Algemeen Rijksarchief) in Brussels. The letters in this file are more or less in chronological order, but without any page numbers.

Letter 1

Letter 1 is a letter written by Brengger, dated 4 December 1604, without an addressee. ⁸⁵ Two copies in different hands are present in the archives. We may assume neither are in Brengger’s hand. Thomas Fincke’s Geometriæ rotundi libri XIIII is cited as 14 libri geometriæ Rolundi. ⁸⁶ Obviously, a scribe must have misread the original. The letter may be a copy of a letter to Kepler. Kepler refers to Brengger’s observations of 9 to 18 November in a letter to David Fabricius of 18 December 1604. ⁸⁷ These are the observations which he shares in the letter. Brengger remains critical of his own observations. He denies the New Star an own motion. He concludes that it has the characteristics of a fixed star, as it sets every day at the same point on the horizon. From his observations, he calculated the position of the New Star to be at declination 21° 15′ and right ascension about 256°. The twilight however prevented him to compare this with fixed stars.

As to the composition of the New Star, he points out that it resembles the primordial matter stars are made up of. The light produced by the New Star resembles that of Jupiter, which leads him to conclude it may have a similar composition. He has not been able to observe a parallax; he fears that he will not be able to determine any such parallax before the Winter’s Solstice.

He conjectures that the cause of the phenomenon may be found in the conjunction of Mars and Jupiter. Although he seems to think that the appearance of this star may be an omen, he leaves the interpretation of it to the astrologers (Figures 10–13).

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Figure 10.

Version 1 of the letter by Brengger. © Algemeen Rijksarchief, Brussel.

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Figure 11.

Signature of Brengger in version 1. © Algemeen Rijksarchief, Brussel.

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Figure 12.

Version 2 of the letter by Brengger. © Algemeen Rijksarchief, Brussel.

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Figure 13.

Signature of Brengger in version 2. © Algemeen Rijksarchief, Brussel.

Letter 2

For letter 2, neither author nor recipient are known, nor is it known when the letter was written. The author seems to have been a keen observer of the skies. Moreover, he is to be sought among Kepler’s correspondents. In the last – preserved – paragraph, he indicates he will write to Kepler. Although the letter is part of a batch relating to SN1604 in the 1604 file, it is clear that it should be dated no earlier than February 1605, but it is more likely that it was written in April or even later. The author after all claims that he observed the New Star on 29 January and gives its coordinates relative to the heart of Scorpio, ⁸⁸ 14° 43′, and the left thigh of Ophiuchus (Serpent-Bearer), ⁸⁹ 16° 50′. He later repeated his observations and gives coordinates which he thinks are more accurate (14° 43′, 16° 45′). These are precisely the coordinates which Kepler in De Nova Stella cites as having been made by Brengger. ⁹⁰ Sommer dates the second observation to 27 March 1605, ⁹¹ this date is not cited in De Stella Nova, but is given by Brengger in his letter of 1 September 1607 to Kepler. ⁹² We can therefore safely attribute this letter to Brengger. This assumption is further attested by other details.

The addressee of Brengger was from Augsburg. Brengger asked him to lend a book for him from the library of D. Heneschius. Heneschius is Georg Henisch (1549–1618), a physician, astronomer, and mathematician of Augsburg. He was a professor at the St Ann Gymnasium and was in charge of its vast collection of 8500 printed titles. ⁹³ Brengger thanked his correspondent for sending him Krabbe’s book on the New Star. ⁹⁴

Brengger observes that the brightness of the New Star, which once exceeded that of Jupiter, is diminishing. It leads him to the conclusion, in accordance with Krabbe, that it will disappear from the night sky. He then goes on pondering on the nature of the New Star (Figure 14).

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Figure 14.

Anonymous letter (Brengger). © Algemeen Rijksarchief, Brussel.

Letter 3

In a letter of 20 December 1604, Michiel Coignet reports to Blasius Hutterus ⁹⁵ on his search for maps which the Archduke had asked for. He has obtained these maps with the Antwerp printer Joannes Vrients. Mercator’s maps were not for sale anymore because his heirs had sold them to Jodocus Hondius in Amsterdam. ⁹⁶

He then turns to the New Star. He claims to have first observed it on 10 October between Mars and Jupiter with a brightness larger than that of Venus, but with a reddish glow and scintillating. From letters he has received from Kepler, he deduces that the latter observed it for the first time on the same day, 10 October, about 17⅛° from Sagittarius and at a northern latitude of 1¼°. He mentions that he has also received letters from Italy in which the same phenomenon is described. ⁹⁷ He will go through them again and report to the Archduke. He further notices that the New Star of 1600 has not disappeared yet (Figures 15 and 16).

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Figure 15.

Letter by Coignet citing Kepler’s observations and making reference to Italian correspondents. © Algemeen Rijksarchief, Brussel.

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Figure 16.

Coignet’s signature. © Algemeen Rijksarchief, Brussel.

Letter 4

Coignet acknowledges he has received a (now lost) letter of the Archdukes, dated 22 December, on 27 December. Apparently, in this letter he was asked about the New Star of 1600 and of the appearance of the new one. He has added a figure of the New Star of 1600 in the constellation of Cygnus. This New Star can still be observed. For the latest news on the New Star of 1604, he refers to the letter of Kepler to the Emperor.

He then goes on to explain the use of an instrument which was sent to Archduke Maximilian III (1558–1618), ⁹⁸ which essentially seems to be a shadow square. It leaves little doubt about the mathematical abilities of Maximilian and his entourage (Figure 17) .

Coignet mentions he also sends the maps, which cost 6 florins 14 stivers.

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Figure 17.

Coignet’s second letter with instructions for the use of a shadow square. © Algemeen Rijksarchief, Brussel.

Letter 4b

A drawing by Coignet of the constellation Cygnus, indicating the new star P Cygni. It is likely this is the figure Coignet was referring to in Letter 4 (Figure 18).

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Figure 18.

Coignet’s drawing of Cygnus indicating the position of the new star. © Algemeen Rijksarchief, Brussel.

Letter 5

This is an undated, and hitherto unpublished, letter by Kepler to Emperor Rudolf II. The letter is written in the same hand as Coignet’s letters, indicating this is a copy of the copy of Kepler’s letter sent to Coignet.

Kepler first mentions that he has moved to a new house, as if to provide an explanation for tardiness.

In this letter, he draws the attention of the Emperor to the appearance of a New Star. Kepler also laments about the inaccuracy of his instruments. He gives the coordinates as 17⅛° Sagittarius and at a northern latitude of 1¼°, precisely the coordinates Coignet also gave in letter 3. The Star is brighter than Jupiter and Venus with a scintillating reddish glow. Kepler states that he has observed the New Star on neither 21 September nor 3 October nor 8 October. He then claims he has observed the New Star yesterday. He deduces that it appeared between 3 and 10 October. He finds similarities with the New Star of 1572.

The fact that Kepler suggests that he has observed the new star yesterday suggest the letter was written about 17–18 October. The first report of a sighting of the New Star to the Emperor was by Johannes Brunowsky, an official in the retinue of Vice Chancellor Rudolph Corraducius and an amateur meteorologist, on Monday, 11 October. ⁹⁹ At first, Kepler doubted the existence of the phenomenon. The following days were cloudy, and he could not make any observations. On 17 October, the sky cleared and he could observe the New Star. ¹⁰⁰ Kepler’s letter seems to be an early report of his observations and can therefore be dated as the second half of October and more likely than not 17–18 October (Figures 19 and 20).

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Figure 19.

Kepler’s letter to Rudolf II. © Algemeen Rijksarchief, Brussel.

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Figure 20.

Signature in Kepler’s letter. © Algemeen Rijksarchief, Brussel.

Letter 6

This is not a letter as such, more a kind of astrological treatise about comets and the New Star. The text has not been added to the appendix, as it adds nothing to our understanding of the history of the sighting of SN1604. The author of this treatise claims the New Star appeared on 6 October. He saw her when he observed the conjunction of Mars and Jupiter. He ascertained her existence the next day. Later observations in November showed it had no parallax, putting her in the eight sphere. It should be considered a fixed star. He then goes on it has the same features as the New Star of 1572. He considers the New Star to be a dry and hot exhalation.

The treatise draws some attention because a number of elements seem to point at Coignet as an author. The first one is the title “Discúrso sobre las estrella núeua que ha parescido este ańo de 1604” which is similar to Discorso sopra la nuova Stella, the title of the book he is, according to Alberi, supposed to have written with Paul Arnerio. Moreover, the author refers to his Theoricas de Planetas for an explanation of the parallax. Coignet has, on several occasions, referred to his soon to be published Theoricas Planetarum, but which, to our knowledge, was never published. On the other hand, the author claims he observed the New Star for the first time on 6 October, while, in letter 3, Coignet claims he first saw it on 10 October. In this letter, Coignet, unlike this author, gives, as any mathematician would do, two coordinates to determine the position of the New Star. Furthermore, the author claims to be 44 years of age, while in December 1604, Coignet had reached the age of 55. We can therefore rule out Coignet as the author of this treatise (Figures 21 and 22).

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Figure 21.

Spanish astrology treatise on SN 1604. © Algemeen Rijksarchief, Brussel.

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Figure 22.

Astrological diagram accompanying the Spanish astrology treatise. © Algemeen Rijksarchief, Brussel.

Science and the Archduke

Although the lives of the Archdukes have been described in detail, we hardly know anything about their interest in science. ¹⁰¹ This contrasts sharply with what we know about their interest in the visual arts.

A comparison with other courts of the age may shed some light on the question.

The Low Countries are at the crossroads of the Gallic and the Germanic cultures. Economically and artistically, at this point in time, they were a continuum with the Rhineland. Trade relations with Central Europe were excellent. Moreover, since 1555, they were governed by the Spanish King. Albert’s court in Brussels therefore was a crucible of influences from all parts of Europe.

During the sixteenth century, a culture had developed at the courts of German princes in which they vied with one another to have the most beautiful, most elaborate, and most precise clockwork mechanisms, such as celestial spheres and astronomical clocks. ¹⁰² This competition also led some princes to actively engage in astronomical research, such as Wilhelm IV of Hesse-Kassel (1532–1592) or August of Saxony (1526–1586). ¹⁰³

Rudolfine Prague must have been one of the most cosmopolitan European cities of its age. Rudolf’s reluctance to travel made the city a magnet for practitioners of the liberal arts. ¹⁰⁴ Science at Rudolf’s court is invariably associated with Tycho Brahe and Kepler, but they were by no means the only notable natural philosophers. Tadeús Hájek, Rembert Dodoens (1517–1585), Caspar Štehlíh of Ceŭkow (1571–1613), Bartholomeus Scultetus of Görlitz (1540–1616), and Johann Jessenius (1566–1621) frequented the court. Most of these scientists held beliefs of an astral influence on events on Earth. Jost Bürgi (1552–1632), the instrument maker, once in the employ of Wilhelm IV produced a planet clock for Rudolf according to both the Copernican and the Ptolemaic world systems. The clock is littered with mythological and astrological scenes. ¹⁰⁵ Tycho’s rival, Nicolaus Raimarus Ursus (1551–1600), a student of Bürgi, was mathematician to the Emperor. ¹⁰⁶ The Emperor himself was highly superstitious and prone to the influence of astrologers.

In Spain, where Albert and his spouse Isabella were raised, less attention was paid to the sciences, although there was a particular interest in medicine and mathematics. The Escorial had its own alchemical laboratory. Nevertheless, Philip II did not share his cousin Rudolf’s enthusiasm for this science. ¹⁰⁷ Juan de Herrera succeeded in convincing Philip of the need for an Academy where mathematics and engineering would be taught. Philip later tried to erect similar schools in all Castillian towns. ¹⁰⁸

Closer to Brussels was the court of Prince-Bishop Ernest of Bavaria (1554–1612) in Liège. He was an accomplished mathematician, which was acknowledged by Adriaan van Roomen (Romanus (1561–1615)) and Gregory of Saint Vincent (1584–1667). In Liège, Ernest tried to emulate Rudolf’s collections, albeit on a less grand scale. ¹⁰⁹ His library and his instrument collection astonished his visitors. ¹¹⁰ Ernest’s court mathematician Zieckmesser claimed he was the inventor of the sector, an early calculating device ¹¹¹ (Figure 23).

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Figure 23.

Solving the equation ( 5 / x ) = ( 1 / 2 ) using a sector. Both legs of the sector carry a scale for square roots. Open a compass to length 1, open the sector such that the points of the compass fit between the markings 5. Open the compass to length 2, we find that the points of the compass fit between the markings 20. Therefore, x = 20.

Michiel Coignet is also dubbed one of the fathers of the sector. One of his manuscripts on the sector, kept at the Bibliothèque nationale in Paris, bears the coat of arms of the Archdukes. The references to the positions of stars indicate that it was written in early 1604. In the preface of the very similar manuscript in the Bodleian library, Coignet claims he first crafted this type of sector for the Archduke. The sector he describes in these manuscripts has sighting vanes and can be used as a surveying instrument. ¹¹²

By the second decade of the seventeenth century, Coignet had developed his sector into a pair of sectors that bear a superficial resemblance to Galileo’s sector (Figure 24).

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Figure 24.

A pair of Coignet type sectors (front and back), from a manuscript of the Antwerp College. © ARAA T14/034 1881.

We know Coignet became a court mathematician, but we hardly know what this entails. We know he provided instruments to the Brussels court. He received orders for instruments from the Court at Brussels and could send them to their recipients using the postal service between the Habsburg courts. ¹¹³ He also instructed army officers in the use of his instruments. In his manuscripts on the sector, Coignet devotes a lot of attention to military subjects such as schematic plans for bastionized fortifications, determining the content of gun powder barrels or the formation of platoons of soldiers.

Clearly, Albert would have been interested in the art of fortification, at that time, the most geometrical of military arts, soon to be overtaken by ballistics. This should not come as a surprise, the war in the Netherlands consisted primarily of siege warfare, and armies would not necessarily confront each other in the open field. From the mid-sixteenth century onward, Italian-style bastionized fortification began to be introduced to the Low Countries. A defending army could retreat into a fortified town, and the attackers had to lay an often long and costly siege. By the mid-seventeenth century, Netherlandish fortifications were without peer, their ditches and ramparts giving them an incredible passive resistance, while the outworks, with ravelins, demi-lunes, and horn works, gave a nearly unsurpassable defence in depth. ¹¹⁴ A commander or a general would ignore the science and art of fortifications only at his own expense.

Duerloo asserts that Albert tried to convince foreign instrument makers to come to his court in Brussels, ¹¹⁵ but all these endeavours seem to have been undertaken after the Truce of 1609. The archducal envoys and agents seem to have had, apart from their diplomatic briefs, the task of providing Albert with state-of-the-art mathematical instruments and time pieces. ¹¹⁶ Unfortunately next to nothing is known about Albert’s collection.

With the exception of cartography, we do not see a real interest in science at Albert’s court. Cartography had always been a theme of interest at the Brussels court ever since Jacob van Deventer had produced his maps of the Low Countries.

The Archdukes tried to lure craftsmen, and not only artists, to the Southern Netherlands, in many cases, but not always, these were people who had fled the south. Among them were the globe makers of the van Langren family. Originally hailing from Gelderland, Jacob Floris Van Langren (c. 1525–1610) had moved to Amsterdam. His son Arnold-Floris (1580–1644) incurred so much debt that he had to flee the bailiffs in 1608. He went to the Southern Netherlands and received £300 towards the cost of this move. He must have had extraordinary social skills because the next year, 1609, he could call himself “Spherograeph van hunne Hoocheden Serenissime” (Spherographer of their Highnesses). He would receive similar amounts on an irregular basis in the following years. ¹¹⁷

Astrology and the Archduke

It was not unusual in sixteenth-century Europe to have a mathematician cum astrologer at court. ¹¹⁸ While a physician used astrology to determine the best date for certain procedures, such as bloodletting, ¹¹⁹ astrologers would cast horoscopes of newborn princes, would make prognostications regarding illness and death of royalty and popes and would interpret unexpected celestial phenomena, such as comets and New Stars. ¹²⁰

In the Netherlands, the first court astrologer who can be identified is Franciscus Monachus (c. 1490–1565), who was consulted by Margaret of Austria (1480–1530) in the 1520s. ¹²¹ Monachus was a Franciscan friar who was associated with Leuven University. The study at the University, with a thriving medicine department, flourished and many of its professors were consulted by regents and the Emperor. ¹²² Both Gemma Frisius and his son Cornelius Gemma (1535–1578) ¹²³ were among them. The year 1580 marks the end of Leuven’s astrological culture, ransacked by Spanish troops and struck by an outbreak of plague, many of the University’s professors perished or succumbed to the disease. ¹²⁴ A couple of decades later, the University of Leiden had taken over Leuven’s position as a leading centre for mathematics, astrology included. However, by the beginning of the seventeenth century, astrology’s status had begun to wane in the Low Countries. ¹²⁵

Whether or not there was a court astrologer at Albert’s court is uncertain. Undoubtedly, his physicians would have used it in their practice. ¹²⁶ However, Albert’s court mathematician, Michiel Coignet, cannot be easily put into an astrological corner. Whereas Kepler’s astrological pursuits are well-known, no such texts exist in the books or manuscripts of Coignet. On the contrary, Coignet always limits himself to the technical level: algorithms to solve an algebraic problem and procedures to use an instrument, all larded with numerous examples.

Only in his later years do we find circumstantial evidence which may point to some astrological connection. In 1616, he is mentioned in the accounts of the Guild of St Luke as astrologus. ¹²⁷ Given the semantic confusion of words like astrology and astronomy, this does not have to have any further bearing. Coignet is known to have signed almanac for 1617 and 1626, so it is quite conceivable that he has also calculated those for the intermediate years. ¹²⁸ May be, with his strength dwindling, he saw it as a convenient source of income during hard times.

Conclusion

The most difficult question to answer is, “why are these letters in the archducal archives?” Duerloo, in his biography of Albert, suggests that

Albert believed that there was some connection with the almost simultaneous capture of Ostend. Perhaps he even entertained the idea that it had a bearing on his imperial ambitions. Still, as supernovas go, their apparition in the skies is spectacular but fleeting. As the star faded, so did Albert’s interest. ¹²⁹

As we have shown in the previous paragraphs, we hardly know anything about science at the Court of Albert, neither do we know anything about his astrological beliefs. Duerloo’s paragraph contains a lot of presumptions, suppositions, and speculation. Letter 6 supports his vision, the others do not. Letters 1 to 5 contain observational data of good quality, without any astrological speculation. It would have been astonishing had there not been any interest in the supernova. Supernovae may be spectacular and fleeting; in naked-eye astronomy, they are in fact extremely rare. ¹³⁰ With the possible exception of the appearance of comets, any change in the night sky is uncommon to observe with the naked eye, to say the least.

With hindsight, we know that Coignet’s generation was exceptional in the sense that they saw two supernovae in their lifetime. However, for an observer in the early 1600s, a supernova or the appearance of a variable star would have been a similar event: the appearance of a new luminary appearing in the heavens. If there was one thing these phenomena did, it was shattering the view that no change was possible in the superlunary spheres. ¹³¹

However, some credence may be given to the hypothesis that Albert may have entertained that the appearance of SN1604 had some astrological significance. Coignet mentions that the new star which had appeared in August 1600 could still be seen. The dates of the appearances nearly coincide with the beginning and end of the siege of Ostend. It would be about August 1600 that the plans for laying siege to Ostend were first conceived. During the Summer of 1600, Albert’s troops were defeated in the battle of Nieuwpoort. However, Stadtholder Maurice’s troops were too weak to lay siege to the city itself. They withdrew from Flanders back to Zeeland. ¹³² Albert’s troops subsequently encircled the last States’ stronghold on the Flemish coast: Ostend. The proper siege began on 5 July 1601 ¹³³ and would not end before 22 September 1604. If one is willing to see a causal relationship between the siege and the New Stars, it is easy to draw wider ranging conclusions about the fate of the Archduke.

The civil war in the Netherlands may, to a certain degree, explain the Archdukes’ lack of interest in science. At least in the period before 1608. The revival of the arts in the Southern Netherlands stands in stark contrast with the fate of the sciences. ¹³⁴ At the court of the Archdukes, interest in science seems to have been largely limited to those sciences which bear a direct relation to practical applications in military matters, such as fortifications. The letters presented here may indicate that this is only part of the story and that there was a genuine interest in other sciences. More research on this topic has to be done to be able to get a clear picture of the attitude of the Archdukes towards science. This task is complicated by the fact that letters or other texts are dispersed over many files in a huge archive spread over many Western European institutions.