G. B. Hodierna's Observations of Nebulae and His Cosmology

As it will be shown in this paper, an earlier drawing of the Orion Nebula, showing three of the stars of the trapezium, was published by Hodierna in 1654 (see Figure 3). However Hodierna's drawing can hardly be termed a ‘map’ of the nebula; instead it seems intended to convey the information of a partially unresolved nebulosity in that region.

For the complete title see Appendix 3.

For other aspects of the personality of Hodierna we refer to the biographical and bibliographical notes in our paper “Light, colors and rainbow in Giovan Battista Hodierna”, in Annali Istituto e Museo di Storia delle Scienze, viii (1983), 59–75.

This is the order of presentation as stated by the author in the “Opusculi Distinctione” at the beginning of the book. Actually Hodierna has followed a somewhat different order (see Section 3 below).

Hodierna G. B. , Nunzio del Secolo Cristallino, edited by Licitra Angelo (Ragusa, 1902). For a comment on this work see Dollo C. , “Astronomia e Profetismo nel Nunzio del Secolo Cristallino di G. B. Hodierna” in Atti del Convegno di studio di S. Margherita Ligure (26–28 Ottobre 1978) (Florence, 1979), 241–53.

Hodierna , Nunzio…, 13–14.

The last page of his Medicaeorum ephemerides (1656) contains an index of works of Hodierna, amongst which is included this Atlas, which apparently was never published. Still in 1657, in a letter to Carlo Tomasi, he writes: “…day after day [after the elaboration of the theory of the Galileian satellites] new and never seen phenomena appear in the sky to the observer: And while I am working hard to represent to the scholars the constellations of the starry sky with maps, I have now to observe and admire from this southernmost region of Sicily some stars that are of southern declination and are not seen in Europe … because I have to show them to the scholars of celestial phenomena, in order that they can see them with their eyes” ( Hodierna G. B. to Tomasi C. , 27 December 1657, in Maggio F. M. , Vita, e morte del venerabil P. F. Alipio … (Rome, 1657)).

The extant ms. maps appear to be preparatory drafts at various stages of refinement for the sky atlas. In many of these maps the nebulae are represented by symbols to distinguish them from stars.

He states: “It is in fact impossible to observe and describe all Nebulosae and Obscurae stars…”(p. 11). Many nebulae are only mentioned, without any description. The maps in his manuscripts show more objects than those described in this book. Unhappily many of these maps have more the character of sketches rather than of quantitative finding charts and are sometimes difficult to interpret.

Riccioli G. B. , Astronomiae reformatae tomi duo… (Bologna, 1665), 41 (§ 3), 158 (§ 35), 364 (1646), 370 (1652 and § 4), and 371 (§ 5).

Hodierna G. B. , Observationes eclypsium anni labentis 1654, see Appendix, ms. 8.

“Eadem est igitur omnibus communis forma substantialis: Videlicet, multitudo Stellarum in coitum conspirantium: Sed non omnibus eadem forma accidentalis…” (De admirandis…, 4).

We know little about Hodierna's telescope. It is very likely that he had more than one. We know that, at least from 1653, he had a telescope made by Francesco Fontana (Variae observationes stellarum…, f. 25., see Appendix, ms. 1). From the number of stars resolved in the Pleiades, in NGC 6231 and in Orion's Trapezium it appears that it had a limiting magnitude near m_v = 8. In a passage of the letter to Juan Caramuel published together with the Saturni systema (1657), writing about the moon of Saturn, he says: “In fact, as I understand from the words of Huygens, it can be seen only with large and perfect telescopes, which enlarge at least 50 times: But my tube increases the diameters of visible objects only 20 times. … And I am surprised that even in Rome, where large telescopes of 30 and 40 palms [1 palm ∼ 26.4 cm] are wonderfully crafted by the excellent craftman Eustachio de' Divinis, this moon has not yet been seen…. But I do not give up hope; in fact as soon as I obtain a very good telescope from the Grand Duke of Tuscany … I hope I will be able to see this moon discovered by Huygens, but also the ones that Renatus de Chartres [sic!] has seen with his wonderful telescopes near Jupiter intermingled with the Medicean satellites.” Reference to a linear magnification of 20 can also be found in the manuscript Compendium caelestium observationum (f. 10, see Appendix, ms. 4).

“Interim, si peroptimo & permagno Tubospecillo hae Caeli partes, quae alioquin caecae videntur, prospiciuntur, statim Stellarum congeries apparebit” (De admirandis, 27).

Hodierna's definition of Luminosa is: “Porrò Luminosam Stellam, vel (congruentius) Constellationem, eam esse reputandam censemus, quae cum sit etiam Stellarum adinvicem coeuntium tumoltuosa coadunatio; tamen, sive quatenus hae Stellae nobis propinquiores existant; sive quatenus maiores sint & spatiosioribus abinvicem intervallis dissitae, partes ad visum patulae fiunt, prout patet evidentissimè in Coma Berenicis, quae cùm sub nota unius Luminosae Stellae à Ptolomeo indigitetur, Stellarum tamen densa multitudo in eo Caeli Tractu, nudis oculis attenditur. Secus autem accidit in Stellis nebulosis, quia in illis Caeli Tractibus nullae Stellae conspicuè cernuntur, sed omnes latent sub nebuculae specie, prout patet evidenter in Nebulosa Praesepis” (De admirandis…, 4).

“Nebulosae Stellae encomio, illum Coeli eminentissimi Tractum, vel Nexum decorandum venit, qui ad immediatum, seu nudum oculorum intuitum nebuculae speciem adamussim repraesentare valeat, quamvis deinde, ubi oculus prospicientis Tubospecillo corroboretur, nequamqu[a]m nebulosus nexus, aut simplex Stella, sed copiosa Stellarum coadunatio circumspectari videatur” (De admirandis…, 3). This definition closely corresponds to Lacaille's second class nebulae and to de Chéseaux's first (see Jones Glyn K. , The search for the nebulae (Chalfont St Giles, Bucks, 1975), 37 and 45).

“Occultae vero Stellae encomio, angustissimus ille Caeli nodus insigniri debet, & dignus reputari, qui cum ad liberum, seu immediatum oculi intuitum, quasi Stella nubilo Caeli Tractu obducta appareat, nihilominus ubi oculus prospicientis Tubospecillo munitus fuerit, & eumdem Caeli nodum excernere contigerit, tunc non Stellam simplicem, sed aut multiplicem, partibus distinctis, aut caecum quodam lucis iubar, indivisum cernere videbitur. Et consequenter Stella occulta nil aliud esse perhibet, nisi arctissima tenuissimarum Stellarum in profundiori sinu coadunatio, quam vix oculus, Tubospecillo corroboratus, excernere poterit” (De admirandis…, 3).

“At Stellae, quas Ptolomeus Occultas, Copernices vero ac Recentiores Obscuras appellant, nequaquam Nebulosos tractus dixeris, sed Stellas caecas, nebuloso quodam quasi velamine obductas repraesentant; quatenus huiusmodi Stellas, non aequè transpicuas, & luminis claritate praeditas, sicuti, & reliquas Caeli Stellas excerneres: Utrumque obscurum genus: At Nebulosum omnibus patulum, & evidentissimum ob insignem magnitudinem: Occultum vero valde exiguum, & absconditum, ita ut non nisi vehementi oculorum conatu à caeteris Stellis excerni possit” (De admirandis…, 1).

“Diffinitio II. Occultae vero Stellae encomio, angustissimus ille Caeli Nodus reputandus erit, qui cum ad Liberum intuitum quasi Stella nubilo caeli tractum obductum appareat, nihilominus ubi oculus prospicientis Optico Tubo eumdem Caeli Nodum excernere contingerit, adhuc non stellam simplicem, sed caecum quodam Lucis Iubar quod cometulum repraesentet, cernere videbitur. Et consequenter Stella Occulta niil aliud esse videtur, nisi angustissima tenuissimarum Stellarum, in profundiori caeli sinu coadunatio, quam neque oculus Tubospecillo corroboratus, aequè adhuc excernere possit” (De coeli characteribus admirandis, f. 5; see Appendix, ms. 3).

Ashworth W. J. Jr , “Halley's discovery of NGC 6231 and the hazards of early star nomenclature”, Journal for the history of astronomy, xii (1981), 1–10.

Jones Glyn , op. cit., 38.

Jones Glyn , op. cit., 21, 42–43, 64.

For the rediscovery of M36, M37 and M38, see Jones Glyn , op. cit., 43 and 66.

Jones Glyn , op. cit., 8 and 9.

Jones Glyn , op. cit., 67.

This interpretation seems reasonable if one considers that M47 (item 1 in this list) is actually east of Sirius, so that Hodierna might very well have given to M41 a qualification belonging to M47.

Jones Glyn , op. cit., 21.

“Harum quamplurimae in Galaxia, vel iuxta Galaxiam attenduntur, …: à via Lactea vero quam paucissimè removentur: Neque enim à Lactea zona substantialiter differre videntur, ut ob id partes Galaxiae ab ea avulsae, censeantur esse, ac reputentur” (De admirandis…, 1).

“Frustra decipiuntur igitur, qui Stellarum Nebulosarum, vel ipsius Galaxiae materialem substantiam, aliud non esse, nisi ipsius Aethereae substantiae coarctatam, seu condensatam portionem autumant, …” (De admirandis…, 24).

De admirandis…, 25.

De admirandis…, 26.

It is perhaps worth noting that all answers given by Hodierna to the proposed problems are introduced by the Latin dubitative conjunction an.

De admirandis…, 54.

“Nam ex eadem substantiae mole, qua simplex ingens Globus conflatur plures etiam, sed exigui Globuli concorporari possunt. Sic fortasse fieri poterit, ut ex invisibilibus Stellis coeuntibus latenter innumeris, confletur unum quid compositum, & appareat ingens Stella recentissime a mortalibus visenda” (De admirandis…, 53). Although this theory seems to refer to the phenomenon of novae, Hodierna does not give any explanation of their fading. Moreover we wish to point out that in Il Nunzio Pio… (Appendix, 7) he gives an explanation of the recurrent Nova in pectore Cygni (P Cygni), which he observed since the beginning of 1654, in terms of radial motions of the star.

In the fourth section of the De admirandis… Hodierna describes a few of his observations of double stars. The reason for this discussion is that most of Ptolemy's and Tycho's Obscurae turned out to be double or multiple stars.

De admirandis…, 54.

Whiston W. , Praelectiones astronomicae (Cambridge, 1707), translated as Astronomical lectures (London, 1715, 1728), p. 42 of the 1728 edition. Courtesy of M. Hoskin.