From Mythology to Astronomy: Lists and Catalogues of Variable Stars

Introduction

The discovery of the new stars of 1572 and 1604 definitely showed that changes indeed occur in the firmament, that is, in the sphere of the fixed stars. Once the novelty wore off, astronomers began to find more and more such stars that were not seen (or noticed) previously. The first among these were the “real” new stars, those we call today eruptive variables (like supernovae). There were, however, other types: the variation of Mira Ceti and Algol were discovered in the 16th to 17th centuries, quite soon after the first SNe. ¹

Noting new stars in the sky led astronomers to investigate the literature for similar occurrences. Star catalogues were also consulted. This activity resulted in several spurious claims, and the list of new stars became quite long. Giovanni Battista Riccioli (1598–1671) in 1651 mentioned 16 such objects in his Almagestum Novum, ² while in 1672 the Italian astronomer Geminiano Montanari (1633–1687) was of the opinion that

there is not one Constellation, which serveth not for an Instance of wonderful Novelties and frequent Changes, either by the Accession of New Stars not discover’d before, or by the Extinction of some of those that had been observ’d formerly, or by increase of Light in some, or the diminution of it in others. ³

In a letter to the Royal Society, Montanari mentioned changes in more than a hundred stars. ⁴ Another diligent observer was the Italian born Parisian astronomer Giovanni Domenico Cassini (1625–1712), who also reported variations occurring in the heavens. Some of these are given only in a general way:

For example, he [i.e. Cassini] hath observ’d one of the Fourth magnitude, and two of the Fifth in Cassiopea, where ’tis certain they were not seen before, many Astronomers having exactly reckon’d up the very smallest Stars of that Constellation, and yet not one of them mention’d those three. He hath discover’d Two others, towards the Beginning of the Constellation of Eridanus, where we were sure they were not yet about the end of the Year 1664, considering that this place of the Heavens, where passed the then appearing Comet, was diligently beheld by many, who perceived divers other small Stars, without observing those two. ⁵

Such a description is not helpful in identifying the stars. In other cases, they are more recognizable, and they will be discussed later.

In what follows I will discuss several such lists of stars, starting with Riccioli and finishing with the very important paper of Edward Pigott (1753–1825). Pigott observed and discussed most of the then known and suspected new/variable stars, with the aim of discriminating between real and spurious variables. His work was a complete success: those stars he classified as real variables are considered variable stars today, while those he dismissed, are either not variables, or have such low amplitudes that they were unrecognizable at his time. ⁶

There is, however, a great difference between the work of Riccioli and that of Pigott. Riccioli belongs to a tradition that lists similar objects together with their assumed effects on humanity. Such are the cometary historiae. ⁷ As Adam Mosley noted, “they were the preserve of historical astronomy, in other words, cometary histories and catalogues were produced by individuals with an interest in historical astrology, and were used in defence of the claim that comets were portents of ill-omen.” ⁸ Pigott, on the other hand, was interested in the stars themselves, whether they were indeed variables, and in the nature of those that were really variable.

The early lists of new stars: 17th century

After the appearance of the new star of 1572, astronomers looked for similar phenomena in the – not necessarily astronomical – literature. They found several candidates, such as the “missing Pleiad,” Hipparchus’s new star, and similar objects. These can be found in various reports on the 1572 and 1604 SNe and similar works. The most important of these, however, was the extensive summary of astronomy by the Jesuit astronomer Giovanni Battista Riccioli. ⁹

Riccioli devoted the second part of the eighth book of Almagestum Novum to new stars. ¹⁰ There he listed the stars themselves, and discussed observations and theories. His list of 16 new stars is the following:

This list is clearly very heterogeneous. The missing Pleiad ¹¹ – which appeared in such lists even in the 19th century ¹² – belongs to mythology. ¹³ Hipparchus’s new star is well known from Pliny, ¹⁴ while the next four were culled from historical works and poetry. Riccioli took the first one of those four from Tycho Brahe, ¹⁵ but its source is possibly the Roman historian Cassius Dio (c. 155–235):

καὶ τέλος ἀστέρα τινὰ αὐτός τε ὁρᾶν ὡς καὶ τοῦ ’Αντινόου ὄντα ἔλεγε καὶ τῶν συνόντων οἱ μυθολογούντων ἡδέως ἤκουεν ἔκ τε τῆς ψυχῆς τοῦ ’Αντινόου ὄντως τὸν ἀστέρα γεγενῆσται καὶ τότε πρῶτον ἀναπεφηνέναι.

Finally, he declared that he had seen a star which he took to be that of Antinous, and gladly lent an ear to the fictitious tales woven by his associates to the effect that the star had really come into being from the spirit of Antinous and had then appeared for the first time. ¹⁶

This object also belongs to mythology. ¹⁷ The next two stars on Riccioli’s list (Nos. 4 and 5) refer probably to the comet of 390 (C/390 Q1). ¹⁸ Riccioli named the German humanist Johannes Cuspinianus (Spießhaymer, 1473–1529) as his source for the new star in 389 and the Byzantine historian Nicephorus Callistus (14th century) for that in 392. ¹⁹ Cuspinianus obtained his text from the chronicle of the historian Marcellinus Comes (6th century), but the original source is probably the ecclesiastical history of Philostorgius (c. 368–439). ²⁰ An alternative interpretation will be given below.

The star supposedly appearing in 398 is taken from a poem of Claudian (c. 370–c. 404). ²¹ This may or may not be a daytime visibility of Venus as Tycho thought. ²²

More interesting are the next two objects, those supposed to have been seen in 945 and 1264. These were reported by the Bohemian astronomer/astrologer Cyprianus Leovitius (1524–1574) in his short tract on the new star of 1572. ²³ Though there were comets visible in these years, ²⁴ Leovitius’ description – both stars were thought to have appeared around Cassiopeia and Cepheus – does not fit them very well. Without independent confirmation their existence is improbable but not impossible. ²⁵

The new stars of 1572, 1600 and 1604 (Nos. 9, 11 and 13 on the list) need no special mention. The case of Mira Ceti is more interesting. The 10th and 16th items actually denote the same star, they refer to its observations by the German pastor David Fabricius (1564–1617) in 1596 and by the Franeker professor of philosophy, Johannes Phocylides Holwarda (1618–1651) in 1638, respectively. Fabricius’s sighting of the star is sometimes regarded as without significance, and Holwarda is taken as the discoverer of the variability of the star. ²⁶ Fabricius’s discovery, however, was known in contemporary Europe: it was mentioned for example by Johannes Kepler, Helisäus Roeslin, and Fortunio Liceti. ²⁷ As early as 1642 the Utrecht professor of mathematics, Jacob Ravensberg had already pointed out the identity of the two objects. ²⁸ Fabricius himself observed the reappearance of the star in 1609, and published this observation a few years later. ²⁹ Riccioli, however, did not include either in his choice of the more certain new stars. ³⁰

Item 14 is the Andromeda Nebula from Simon Marius’s preface to his Mundus Iovialis. ³¹ The other star mentioned for 1612 by Riccioli and supposed to have been seen by Jost Bürgi is probably 12 Aquilae. ³² The last two on Riccioli’s list pose some problems in identification. The first (No. 12) had been observed by Kepler on 21 December 1602 while he was inspecting the Moon:

Luna iride vestita angusta, ut hanc inter & marginem Lunae posset diameter Lunae interesse, transiverat stellulam quandam in constellatione piscis, sic ut haec in iride Lunae haereret. ³³

The moon was clothed in a narrow halo, such that the diameter of the moon might be placed between it and the edge of the moon, and it had passed through a certain small star in the constellation of Pisces, so that this star was embedded in the halo. ³⁴

On a marginal note Kepler remarked that he was unable to identify the star, so it could be a new phenomenon. The star appeared in Pisces, though Kepler’s description is too vague for any attempt of identification.

The last object on Riccioli’s list (No. 15) was seen by Václav Pantaleon Kirwitzer (1588–1626), a Jesuit astronomer, originally from Kadaň, Bohemia. He was sent to Goa, India, where, with other Jesuits, he observed the comets of 1618. ³⁵ While watching the second comet they noticed a Venus-like star in the East. It was probably Mercury given that Venus was visible in the evening at that time. ³⁶

These were the new stars usually repeated in the astronomical literature of the time. Some of them were comets, some real variables, some planets. Not every one of them is easily identifiable, and not every one of them is certain to exist.

A similar list was published by the German philosopher and optician Johann Zahn (1641–1707). His list contains different objects from Riccioli’s, so it is worthwhile to review them. Zahn lists the following stars: ³⁷

Zahn, similarly to Riccioli, starts his listing with mythological objects. The first is the well-known star of Bethlehem (Mt 2,2). The second was mentioned in the biography of the Emperor Severus Alexander:

Fertur die prima natalis toto die apud Arcan Caesaream stella primae magnitudinis visa et sol circa domum patris eius fulgido ambitu coronatis.

It is said that on the day after his birth a star of the first magnitude was visible for the entire day at Arca Caesarea, and also that in the neighbourhood of his father’s house the sun was encircled with a gleaming ring. ³⁸

There is another possibly mythological star listed at 1238 (No. 9). Zahn took it from the German theologian Heinrich Eckstorm (1577–1622), ³⁹ whose source was Polydore Vergil (c. 1470–1555), an Italian humanist living in England:

Principio insequentis anni, Henricus suscepit ex Aleonora uxore filiolum, quem Edouardum nominavit, ob memoriam illius divi Edouardi tertii qui paulo ante regnarat, quam Normani Angliam occupassent. Hunc puerum Otho legatus baptizavit, sub cujus ortum apparuit stella immensae magnitudinis per aliquot dies ante solis ortum, quae per longum coeli tractu, veloci, crebroque cursu ferebatur, modo ignem prae se ferens, modo fumum post se relinquens: quo sane ostento, futura Edouardi patris amplitudo, ac Edouardi filii exiguitas vanitasque velut ex oraculo quodam pronunciata dicitur.

At the beginning of the following year Henry fathered by his wife Eleanor a little son whom he named Edward in memory of that that third, sainted, Edward who had reigned a little before the Normans occupied England. The legate Otto baptized this child, and at his birth for several days a star of great size shone a little before sunrise, now showing fire before itself, now trailing smoke after itself, and it was carried over a long tract of the heaven in a swift course, showing both the future greatness of Edward’s father and Edward’s own puniness and vanity, as if by an oracular prediction. ⁴⁰

As Edward I was born in 1239, Zahn’s date seems to be incorrect. It is also possible that the comet C/1240 B1 ⁴¹ was antedated to fit the date of the birth of the prince.

The third item on the list was visible between May and September 380 in Libra. Zahn’s source was Abraham Rockenbach (1536–1611) ⁴² in this case. Rockenbach, a professor of law in Frankfurt (Oder), did not give, however, any reference to this object.

The new star of 393 is more interesting. There was a supernova visible in 393, with an observable remnant. ⁴³ Zahn took the object from the ecclesiastical history of Nicephorus Callistus ⁴⁴ – it is the same object that can be found at year 392 in Riccioli’s list (see above). It is therefore quite possible that the objects of 389, 392, and 393 all refer to the same supernova.

Item 5 may be a comet seen in 583. There are mostly Far Eastern records of its appearance. ⁴⁵ Zahn’s ultimate source, however, is the Frankish History of Aimoin (c. 960–c. 1010). ⁴⁶ The next object may have been also a comet or a nova as well. ⁴⁷ It seems to have appeared first around Christmas, so it cannot have been Halley’s Comet. ⁴⁸ It was seen in December and January next year, near the Pleiades:

Hac tempestate noctu stella iuxta vergilias caelo sereno inter Domini natalem et theophaniam apparuit, omnimodo obumbrata, veluti cum luna sub nube est constituta. Post haec mense Februario die media stella ab occasu exiit, quae cum magnó fulgore in partes orientis declinavit. ⁴⁹

At this time between Christmas and Epiphany there appeared at night in a clear sky a star near the Pleiades shaded in every way as when the moon stands behind a cloud. Afterwards in the month of February at noonday there arose a star in the west which set with agreat flash in the direction of the east. ⁵⁰

This description agrees well with the Japanese records. ⁵¹

The objects for the years 1071, 1172, and 1273 are more uncertain. The one in 1071 was taken from Riccioli, but from his list of comets, not of the new stars. ⁵² Kronk does not mention a comet from this year. In 1172, two new stars were seen, one bright, the other fainter, which at first seemed to be in conjunction, but afterwards separated. ⁵³ The supposed new star in 1273 is quite obscure, it cannot be found in lists of comets or new stars.

Items 11–15 are well known new stars and the Andromeda Nebula. One must note, however, that Zahn knew about Fabricius’ discovery and the identity of the two “new stars” in Cetus even though he listed it as an event in 1637. Item 16 is the nova CK Vulpeculae, discovered by the Carthusian monk Voituret Anthelme (1618–1683) in 1670.

The last item in Zahn’s list is Cassini’s supposed discovery of many new stars (see above). These will take us to another kind of list of new stars: that of stars observed by an astronomer in contrast to the previous practice of selecting them from the literature. The appearance of observers, however, did not stop the practice of publishing the latter. Textbooks, introductory texts of astronomy, and so on usually listed stars that had not been observed by the author.

Observing variable stars

The second half of the 17th century saw the appearance of astronomers who actually observed the stars, not just looked for them in older literature. The French astronomer Ismaël Boulliau (1605–1694) determined the periodicity in the light variation of Mira Ceti and developed a very successful model to explain it. ⁵⁴ “For the very first time, a changing star was lawlike in its behaviour,” as Michael Hoskin put it. ⁵⁵ Robert Boyle also considered it a very notable achievement:

But most remarkable is that Caelestiall Phaenomenon afforded us by the Emerging, Disappearing, and Reappearing Stars of this Age, which have been observed in the Girdle of Andromeda, and in or about the Swans Brest; (which is said to have been seen in the year 1600, and to have vanisht in 1621) and especially that which having above 25 years ago appeared for a while in the Whales Neck among the fixed ones, and afterwards by degrees disappeared, was lookt upon by those Astronomers of that Time who did not outlive it, as a Caelestiall Comet. ⁵⁶

As I already mentioned, there were various claims of discovering variable stars, sometimes hundreds of them. The Philosophical Transactions reviewed the work of Pietro Maria Cavina (c. 1637–c. 1690) from Faenza. ⁵⁷ Cavina accepted the existence of changes in the sky:

whereby he [Cavina] affirms to have found considerable changes in divers of the Fixed Stars from what Bayerus and others have remarked of them, as to Magnitude and Numbers; instancing in Ursa both Minor and Major, in the Dragon, Cefeus, Bootes, Corona Septentrionalis, Hercules, Lyra, Cygnus, Cassiopea, Perseus, and the Via Lactea. ⁵⁸

Cavina’s work is remarkable since it may contain the first indication of the variability of Algol (β Persei). In describing his observations made on the constellation of Perseus, he made note of a second magnitude star in the head of Medusa:

Il Capo di Medusa era di seconda, conforme li Catalogi, e globi antichi, Arato di Colonia, benche Tichone, et altri Moderni l’habbiano posta di terza. ⁵⁹

The Head of Medusa was second [magnitude], agreeing with the ancient catalogues and globes and Aratus of Colonia, although Tycho, and other Moderns have placed it at third [magnitude].

While Cavina did not mention his own observations of this star, he did so in the case of others in Perseus, so one may presume that he had noted changes in Algol, too. Since he published his results 2 years before Montanari, he certainly deserves at least a mention in the history of variable star observations.

Geminiano Montanari’s fame in variable star astronomy rests on his discovery (but see above) of the light variation of Algol. He observed the star as of the fourth magnitude at the end of 1667, in 1669 it returned to the second, while in 1670 it was again as faint as the fourth:

E se punto applicarete l’occhio allo spaventoso capo di Medusa, scorgerete (& hormai senza pericolo d’impietrirui, se non vi rendesse immobili la meraviglia) che la più luminosa stella, che in esso risplenda, da frequenti mutazioni sorpresa, non possiede, che a vicende i più chiari splendori. Io l’osservava già molt’anni di terza grandezza. Impiccioli del 1667. sino al quarto Lume: del 1669. racquistò i primieri raggi sino al secondo honore; e l’anno 1670, di poco oltre passava i confini del quarto. ⁶⁰

And if you look at the scary head of Medusa, you will see (and now without the danger of being petrified, unless the wonder makes you immobile) that the brightest star that shines there, surprised by frequent mutations, possesses the greatest luminosity only sometimes. I had already observed it for many years as of third magnitude. At the end of 1667 it declined to the fourth magnitude, in 1669 recovered the original rays of the second magnitude, and in 1670 it passed a little over the fourth.

Montanari himself did not derive any period of variation, this was done more than a 100 years later by the English amateur astronomers John Goodricke (1764–1786) and Edward Pigott. ⁶¹

As it was mentioned earlier, Montanari claimed to have observed changes in many stars, more than a hundred. A great many of these were the so-called catalogue variables, that is, stars with discordant values of magnitude in the older catalogues. Montanari tabulated 40 of them, comparing the lists of Ptolemy, the Alfonsine tables, Copernicus, Clavius and Tycho. ⁶² The stars are identified by their Tycho number. The first star is 21 Ursae Majoris and the magnitude values are 3, 3, 3, 2, 4. The star itself is λ (33) Ursae Majoris (the number in parentheses is the Flamsteed number in this case), which is not a variable star. The next two are 20 and 21 Draconis according to Montanari, but Francis Baily (1774–1844) identified them as 21 and 20 Draconis, and Tycho’s brightness values support Baily. ⁶³ These correspond to ω (28) and A (15) Draconis, neither of which is a variable star. The lack of confirmation of variability among these objects is not surprising when one remembers that magnitude was not a well defined quantity until the middle of the 19th century. ⁶⁴

There are stars Montanari suspected of showing changes based on his own observations. The first two were second magnitude stars in Argo Navis, which he was unable to find later. ⁶⁵ According to the report in Philosophical Transactions ⁶⁶ these stars were Bayer’s β and γ. ⁶⁷

Another candidate is the sixth of the Crab, that is, α Cancri. It was a 3rd magnitude star in Tycho’s time, but Montanari claimed it to be of the fifth. ⁶⁸ The star is not a recognized variable.

We find similar descriptions of supposed stellar variability in the case of Cassini, too. He reported them in the Journal des Sçavans in 1671. ⁶⁹ The first is

M. Cassini hath observ’d, that the star vvich Bayerus puts near that vvich he marketh in the Figure of Ursa minor, appears no more; ⁷⁰

The suspected star is near ε Ursae minoris. Pigott could find only a 7–8 mag. star in the vicinity. ⁷¹ There were a lot of changes in Andromeda according to Cassini:

that, which is marked A in the Figure of Andromeda, is also disappear’d; that in lieu of that vvich is marked υ, at the knee of the same figure, there are two others more Nordward; and that that, vvich is noted ξ, is very much diminisht. The Star, vvich Tycho placeth at the extremity of Andromeda’s Chain, and calls it of the Fourth magnitude, is now so small that one can scarce see it. ⁷²

This description illustrates well the difficulties early modern astronomers encountered without proper star catalogues and maps. The last star mentioned in the previous quote, at the end of Andromeda’s chain (No. 22 in Tycho’s list), may be either 81 Cygni according to both Baily and Pigott, ⁷³ or, it is quite possible that Cassini took it to be ο (1) Andromedae, which is at the end of the chain on Bayer’s map. In any case, neither of these stars is variable.

The case of A Andromedae is similarly murky. Bayer took A And to be the 17th in Ptolemy’s list of stars in that constellation. Baily, however, identified A And with 49 And of Flamsteed (or, 21 And of Ptolemy), and 17 of Ptolemy with 54 of Flamsteed. ⁷⁴ Pigott observed some of these stars – 49, 51, 53, 54 of Flamsteed and ξ (46) And – and found no variables among them.

Later lists of new stars: 18th century

The appearance of observers significantly changed the character of the variable star lists. The historical considerations mostly disappeared, their place was taken by a discussion of the properties of the observed stars (position, description of the change of brightness). Though part of the reason for preparing such lists were lost (i.e. astrology), there still remained a strong motivation. To quote Pigott: “so that in future we can examine them without much trouble, and be certain of any change that may take place.” ⁷⁵ Since periodic variables were already known at the beginning of the 18th century (Mira Ceti, χ Cygni), and there were suspicions regarding the possible periodicity of Tycho’s star, ⁷⁶ this was an important function of such lists. There was another significant development at that time: the Altdorf professor Johann Christoph Sturm (1635–1703) introduced the first classification of these stars, dividing them into periodic and temporary variables. ⁷⁷ His work was refined in the following decades, and we find that the chronological lists in several books are replaced by lists according to type.

David Gregory (1659–1708), professor of mathematics at the University of Edinburgh, followed the traditional way when presenting the stars. He started with the supposed new star of Hipparchus, then continued with the more recent objects ⁷⁸ :

With the exception of the newly added object of 1670, these are the same stars that we find in Riccioli’s lists, without the uncertain phenomena from the literature. Gregory thought that the stars of 1596 and 1638 were the same, indeed, they both refer to Mira Ceti. He knew about the work of Cassini and referred to it.

John Keill (1671–1721), a student of Gregory and later Savilian professor of astronomy at the University of Oxford, also discussed new/variable stars in his astronomy textbook. He mentioned the two types of variables (without referring to Sturm):

Several Stars which were observed by the Antients, are now no more to be seen, but are destroyed, and we have known some new ones come in the Heavens unknown to them; which likewise in due time will vanish, and disappear: There are also some Stars which for a Time are extinguished, and become invisible, but after a certain Period they reassume their former Lustre. ⁷⁹

His examples were usually well known variables: Mira Ceti for the periodic stars, Hipparchus’ and Tycho’s new stars and P Cygni and CK Vulpeculae for the temporary stars. He even described the missing Pleiad. Though he considered Tycho’s star a temporary star, he called attention to its supposed previous appearances (i.e. Leovitius’s stars):

It is probable that these two Stars might have been the same with that which was seen by Tycho, and that in about 150 Years the same Star may again make its Appearance. ⁸⁰

Jacques Cassini (1677–1756), son of the aforementioned Giovanni Domenico Cassini, described some of the variable stars in great detail in his 1740 book, Éléments d’astronomie. ⁸¹ He divided his list into two parts, not according to types of variability, but according to the reliability of our knowledge about them.

First he discussed the missing Pleiad, calling attention to the fact, that using telescopes one can see more stars than six or seven. He mentioned afterwards the well-known suspects from the old literature: the stars of Hipparchus and Hadrian, those that appeared in CE 388, 389 and 398, all of which he thought could refer to the same star. He ended his list of uncertain objects with the two stars claimed by Cyprianus Leovitius.

He also included one more interesting item listed between the 4th century objects and Leovitius’ stars:

Une quatriéme qui fut apperçûe par Messahala Haly & Albumazar, dans le neuviéme siecle, au 15.^e degré du Scorpion, qui parut pendant l’espace de quatre mois entiers, & dont la clarté étoit si grande, qu’elle répandoit autant de lumiére que la quatriéme partie de la Lune. ⁸²

A fourth was discovered by Messahala Haly & Albumasar in the 9th century, at the 15° of Scorpion, that was visible for four full months, and its brightness was so great that it shed as much light as a quarter of the Moon.

The source of Cassini’s statement seems to be the Italian philosopher Fortunio Liceti (1577–1657). ⁸³ It constitutes, however, a merging of two distinct traditions, which may have been done by Liceti himself. ⁸⁴ He referred to the Coimbra Jesuits and to the Louvain professor of medicine, Thomas Fienus (1657–1631). The Jesuits mentioned Albumasar (Abū Maʿšar, 787–886) and Haly (Hali in the text, Ibn Riḍwān, 998–1061 or 1069) separately, though it is possible to connect them. ⁸⁵ Fienus, however, reports only Haly’s observation. ⁸⁶ Albumasar claimed to have seen a comet over the orb of Venus, ⁸⁷ while Haly observed the new star of 1006. ⁸⁸

Here is Cassini’s list of certain variables:

This list does not present serious problems. Apart from some stars mentioned by the elder Cassini and Maraldi, all of these objects are variable stars. Cassini’s list resembles the earlier historiae in that it includes sometimes quite long discussions of the stars, but these are astronomical and not historical or astrological.

Two more lists are worth mentioning before turning to Pigott’s work. The first is “A Table of several new Stars, Nebulae, and double Stars, &c.” found in the Original Theory of the English astronomer Thomas Wright (1711–1786). ⁸⁹ Wright listed 11 new stars. The first was the missing Pleiad: “Lost after the burning of Troy, but now returned; see Ricciolus.” He mentioned one of Leovitius’ stars, that from 945. Besides the supernovae of 1572 and 1604 Wright knew of P Cygni (new star of 1600) and of both discoveries of Mira Ceti, he did not, however, state they were identical, even though their descriptions were practically the same. The last item in Wright’s list was χ Cygni, discovered by Gottfried Kirch (1639–1710) in 1686. ⁹⁰ Wright’s objects are the same as we find in Riccioli’s historia, but with a great difference: the “disasters” have disappeared.

The discussion of new stars in John Hill’s Urania ⁹¹ is very interesting (although it is unfortunately full of misprints). He considered the various claims of new stars very critically. He refused to accept stars that were missing from ancient catalogues as new stars:

With regard to those stars which we see and insert in their places at present, and which have not been named in the catalogues of the antient writers, nor set down in the figures they made of the constellations, we are not to suppose that they were all of them invisible at that time, and have appeared in the heavens only since; this would be to encrease the number of stars at a strange rate, and at a very unfair one. ⁹²

He also excluded those stars that were named new because of some not very clear description by some writers in Antiquity:

To reduce the matter to a certainty, we shall place no great dependence upon the accounts of those new stars mentioned by such writers among the antients as did not make astronomy their study, since they have not ascertained their places, nor is it possible to distinguish, by what they have said, whether those, of which they speak, were fixed stars or comets. Without knowledge and precision, history is blind and useless. ⁹³

He proved his case with a thorough discussion of the missing Pleiad. Other stars previous to the 1572 supernova fared no better. According to Hill:

There is no doubt of there having been appearances to give origin to these observations, but the circumstances, necessary to have been added to the accounts of them, are wanting, and there is no speaking any thing of certainty concerning them. ⁹⁴

In other words, these descriptions are not observations.

According to Hill, the first star to have been observed properly was the 1572 supernova. He listed several variables discovered afterwards, giving positions, magnitudes, and presenting an explanation for their variability. His theory is a modification of Bullialdus’ model, whom he accused of plagiarizing Riccioli. ⁹⁵ Since there were irregularities in the light variation of the periodic stars (Mira Ceti, χ Cygni), Hill accepted the following model:

The possible account of them must be, therefore as already hinted, that they are globes of solid matter, obscure on one part of their surface, and luminous on the other. And as a revolution round about their own axis would account for all the appearances, were they regular, there is this particular motion also in the poles of that revolution round the axis. This will shew us, occasionally, more or less of the enlightened surface; and all the rest will follow from the other. ⁹⁶

Hill’s description of the variables is similar to that of Cassini: there are long discussions of variables, but the astrological part is missing.

Pigott’s work

Edward Pigott’s paper on variable stars is one of the most important papers in early variable star astronomy. ⁹⁷ It contained a variable star catalogue in the modern sense – that is, it listed positions and magnitudes instead of a long text discussing the history and possible effects of the individual objects. Pigott also presented a classification of variables, which was an update of Sturm’s original work incorporating the new short-period stars discovered mostly by Pigott himself and his friend, John Goodricke. ⁹⁸

His catalogue consisted of two parts. The first listed the stars that Pigott thought to be variable (“undoubtedly changeable”). These are the following (modern names are in parentheses if they differ from those given by Pigott):

The stars in this list are all considered to be variable today. The second class contained those 38 stars that “remain yet to be better authenticated.” He did his part in the required authentication, as he himself observed or tried to observe every one of them. The naming of the stars shows the difficulties arising from the lack of an accepted nomenclature. We find names such as “Hevelius’s 6 Cassiopeae,” “Near 53d Eridani” or even “In west scales of Libra.”

Checking the stars in the second list, one can find real variables among them, but with small amplitudes. For example, Flamsteed’s 41 Tauri is an α² CVn variable (GS Tauri) with a visual amplitude of less than 0.1 magnitude. ⁹⁹ Pigott was unable to detect such a small change, and, in fact, found the star constant. There are a few suspected variables in the list, too. For example ξ Leonis has a suspected variable star designation: NSV 4518. ¹⁰⁰ We can also find a few non-existent stars in the list: Flamsteed’s 25 Leonis, 91 Virginis, and 33 Serpentis are all such objects. ¹⁰¹

Pigott’s catalogue changed the way in which variable stars were to be listed. He used a tabular form, giving data such as coordinates and magnitudes. All the supposed new stars collected from chronicles, poems, etc. were omitted. He used only those reports that were made by astronomers and included coordinates. These changes were important: he did not arrive at his conclusions by weighing the merits of various authorities but by observing all the stars in his catalogue. ¹⁰² This tabular form came into general use in the 19th century, with practical data such as coordinates, magnitudes and periods (if there were any). ¹⁰³

Summary

The earliest lists of variable stars looked like the cometary historiae. Instead of numerical data (such as position and magnitude), we find descriptions of the stars, sometimes with their supposed effects on humanity. The objects themselves could be put into three classes: mythological, astronomical, and astrological, there are examples of all three in the earliest such list discussed here, that of Riccioli. The sources of these lists were usually not observations, but a perusal of the literature, not only astronomical but historical, too. The result of this practice were the mythological objects: stars supposed to be in connection with the birth or death of some notable person, or with some significant event in history. The missing Pleiad or the star of Antinous are good examples for this class. The other two types are more or less interconnected, just as astronomy and astrology were in that time. Some objects’ description is focused on their usually malevolent effect on Earth, while others lack such descriptions of impact.

By the end of the 17th century the situation changed. Another source for new stars has appeared, as we can witness in the pages of Philosophical Transactions. Astronomers, like the elder Cassini and Montanari, claimed to have found such objects in abundance by observations. Of course, these observations may occasionally mean only a comparison of magnitudes in older catalogues to the astronomer’s own estimate, but there are cases when several independent observations made by the astronomer were listed (e.g. Montanari and Algol).

There were more changes in the 18th century. The clearly mythological objects started to disappear from the lists – the only exception is the missing Pleiad – and the description also changed in character. Jacques Cassini wrote about the light variations observed in the stars, not about their supposed effects on the Earth. Good examples are the stars of Leovitius: the Bohemian astronomer described them as the causes of various calamities in Germany, while Cassini only mentioned their supposed position in the sky. Moreover, the existence of these stars were taken for granted, and their workings were explained by natural and not supernatural causes.

This process was closed by Pigott, whose work marked the end of the first phase of variable star astronomy. No more mythological objects, not even the missing Pleidad are to be found in his table of variable stars. Neither is there any trace of an astrological description, not even a hint. Instead, he gave such data as coordinates and magnitude limits. Pigott’s and Argelander’s work (60 years later) laid the foundation of modern variable star astronomy.