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Galileo's 1617 observation of the Trapezium, since it was only recorded in a notebook, was probably unknown to any but the closest of his friends. But the Orion Constellation, being one of the most striking constellations in Northern skies, was surely as natural and fascinating a target of investigation in the 17th century as it is today. So, many others undoubtedly looked at it through early telescopes. However, the Trapezium region was probably not widely known until the 1659 publication of Christiaan Huygens' drawing of the famous nebula and the stars within it.
Prior to Huygens' book, possible representations of the Trapezium stars appeared in books published by Anton Maria Schyrleus of Rheita (1645) and Giovanni Battista Hodierna (1652). We are quite confident, for the reasons explained below, that what have been claimed to be the Trapezium stars in Hodierna's diagram are not, in fact, the Trapezium stars. What Rheita may have drawn is less clear.
| Trapezium (?) | Mars |
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In his recent article about Galileo's observations of multiple stars, historian Harald Siebert mentions in passing a diagram (shown at far left) of a triple star in Orion published by Czech astronomer Anton Maria Schyrleus of Rheita in his 1645 book Oculus Enoch et Eliae. Unlike Hodierna's later drawing, Rheita's diagram, which appears as Figure 7 on Sheet G of the engravings at the end of the second volume, does indeed look very much like a representation of the three brightest Trapezium stars (Galileo's g, c and i). However, no scale is given, and Rheita says in the text (on page 198) that he observed this pattern in Orion's belt; whereas the Trapezium is in the sword. Rheita, who is noted for making many improvements to the telescope, was presumably using a Keplerian telescope. This would account for the orientation being upside down to that recorded by Galileo. Rheita's diagram of the Trapezium-like triple star in Orion is accompanied by a diagram of Mars (the right hand figure). The surrounding circle of highly-flattened moons might possibly be segments of a diffraction ring, or some other kind of distortion (such as internal reflections) in his telescope. Rheita says the sketches were made with a "15 pedum" telescope, which we take to mean a 15 foot tube length; much longer than Galileo's. Although Rheita gives no scale, the similarity between the size of Mars and the triple star system also argues for the latter being the three brightest Trapezium stars, despite the imprecise description of its location in the sky.
In 1654, two years before Huygens observation, Sicilian astronomer G.B. Hodierna published a
map of a part of Orion's Sword in which he saw a bright nebula.
Within the boundaries of the nebula he drew three stars.
The map, which is reproduced at the far left, appears on
page 19 of Hodierna's book
De Admirandis Coeli Characteribus,
the first part of which is a catalog of all the nebulous areas in the sky that Hodierna
had observed during his career as an astronomer, a book widely regarded as a
pre-cursor to the later and much more famous Messier catalog.
Since 1985, based on an article by Fodera-Serio et al.,
this diagram has been claimed by many to be an early representation of the Trapezium,
an idea which seems to have gained wide acceptance.
However Hodierna's book also includes (on page 14) a diagram of the Pleiades, indicating that most of Hodierna's plates cover about one degree of sky, a scale at which the Trapezium is not likely to be resolved. It is also apparent (as Fodera-Serio et al. show in the examples in their article) that the printed images need to be inverted to conform to the pattern of stars in the sky.
In the figure at far left we have color-coded, for clarity, the stars appearing in Hodierna's plate. The original figure has been rotated and reversed to place north at the top -- note Hodierna's indication of Occid. (= west) at the right-hand edge. The background speckles that have not been color coded are defects in the printing, and do not represent stars. We assume that the three stars referred to by Fodera-Serio et al. as representing the Trapezium are the three within the central oval, which we have colored red, yellow and green. However, both Galileo and Huygens mentioned that, as seen through a 17th century telescope, the stars are nearly touching, and the stars pictured by Hodierna are clearly not touching: on the contrary, they are shown very widely separated, so it seems unlikely they could actually represent the Trapezium. To the right of Hodierna's plate we show a modern sky chart of this region, also covering about one degree in angle, produced with Patrick Chevalley's excellent Cartes du Ciel sky mapping software. As much as possible the stars in the modern chart have been coded with the colors of the corresponding stars in Hodierna's map, and the brightest stars are labeled with their Flamsteed numbers (e.g., "44" is the 2.8 magnitude star at the tip of Orion's sword, known as "44 Ori", sometimes referred to by its Arabic name of Nair al Saif). Although Hodierna's map is remarkable for showing a crude outline of the M42 nebula, it is quite apparent that the three stars he shows within that outline are Galileo's stars a, b and g (exaggerated in spacing, and distorted in shape). Galileo's stars c and i are not represented (as the modern map properly indicates, they would be very difficult to resolve at this scale), and hence red, yellow and green stars are not a picture of the Trapezium. The Trapezium is represented by the single red dot labeled "41 Ori".
Fodera-Serio et al. indicate that little is known about the telescope(s) Hodierna may have used. Hodierna was an admirer of Galileo, and his own observations probably began in the 1620's. He indicates that many of his observations were made at 20 power. By 1653 he had acquired a telescope made by Francesco Fontana, although of what size and design seems unknown. As late as 1657 he was complaining that he was unable to duplicate Huygens's observation of Titan (the brightest moon of Saturn), and expressed admiration of the long focal length telescopes of Divini that were then in use in Rome (and far better, Hodierna presumed than his own).
We would guess from the large distortions in Hodierna's star maps that his observations were made with a telescope of Galilean design (negative eyepiece). It is not easy to draw accurate star maps of extended regions of the sky with a Galilean telescope. As Galileo himself discovered in preparing the star maps for Sidereus Nuncius, since so little is seen at one time, it very difficult to keep the relative distances in mind, and large distortions occur as one attempts to piece together the many tiny fields of view. Similar distortions to those seen in Hodierna's diagram of Orion's sword may be seen in many of the other star maps printed in his catalog. Hodierna' diagram of the Pleiades, for example, is very similar (both in the number of stars depicted and the large amount of geometric distortion) to Galileo's.
The nebulous region of glowing gas around the Trapezium stars in Orion's sword, known as M42, has become so well known that many modern observers believe they can detect it with the naked eye (they may in fact be seeing the unresolved clustering of the stars Galileo labeled a, b and g in his Trapezium drawing). In ancient times, however, this feature was apparently unrecognized, and the "Orion Nebula" listed in pre-telescopic star catalogs refers not to M42, but rather to the clustering of faint stars that mark Orion's head. Why the ancients regarded the clustering in the Head as "nebulous" while giving no special attention to the similar clustering in the Sword is a mystery. However that may be, Galileo believed he was the first to resolve the glow of the ancient Head of Orion nebula into its individual stars, and included a diagram of the ancient "Orion Nebula" in Sidereus Nuncius.
The first clear published description of the modern Orion Nebula of which we are aware is that by Swiss astronomer Johann Baptist Cysat in his book about the comet of 1618. In describing the appearance of stars seen though the comet's tail, Cysat says something to the effect (crudely translated from the original Latin) that "this phenomenon is similar to the congeries of stars that is in the firmament towards the last star of the Sword of Orion; there truly is seen (by telescope) a congestion of stars in a narrow space and all round and between those stars light diffuses like a shining white cloud". To us, Cysat does not seem to be announcing a new discovery, but rather he seems to be referring to the "shining white cloud" in Orion's Sword as something that would have been familiar to telescopic observers at the time his book was published (1619), and could be cited as an appropriate comparison for describing the appearance of the comet.
The existence of this description, on page 75 of Cysat's otherwise rather obscure book, was pointed out by Rudolf Wolf (of Zurich sunspot number fame) in a brief article published in 1854. Wolf was taking exception to the then-prevailing idea that the nebula had first been described by Huygens. Although Cysat gives no diagram, his description well precedes those of both Huygens (1656) and Hodierna (1645; of which Wolf was probably unaware).
Later, in a series of articles on the history of astronomy in France published during World War I, Guillaume Bigourdan pointed out what he believed was a still earlier (albeit unpublished) description of the modern Orion Nebula by French nobleman, and friend of Galileo, Nicolas-Claude Fabri de Peiresc. Since the publication of Bigourdan's article, Peiresc has been widely credited as the discoverer of M42.
Peiresc's description consists of a series of entries (written in Latin) in an observing diary which Bigourdan found among Peiresc's papers stored in the provincial library at Charpentras. The entries which Bigourdan transcribed cover portions of the period November 26, 1610 - January 15, 1611. Peiresc later requested, and received, from Galileo the lenses used for making, in collaboration with his friend Pierre Gassendi and the artist Claud Mellan, the extraordinary engravings of the Moon; but he was presumably, at this time, attempting to confirm and extend the observations reported in Galileo's recently-published Sidereus Nuncius using a telescope of local French manufacture (some of which had been available from before Galileo heard of the invention). According the biography of Peiresc on the Galileo Project website, this telescope had been acquired by Peiresc's patron Guillaume du Vair, president of Parlement of Provence; and Peiresc's observations of the satellites of Jupiter and the Orion nebula were confirmed by his friend Joseph Gaultier (but, see below: Gaultier's observations of Jupiter probably actually preceded Peiresc's, and we can find no reference to what Gaultier saw in Orion).
Peiresc's telescope of 1610-1611 was evidently considerably less powerful than Galileo's, for in the January 15 entry, describing the stars in the Beehive cluster in Cancer, he counted only 15 stars compared to the nearly 40 recorded by Galileo (and later, Hodierna). It may also be significant that Peiresc refers to this clustering of stars (as did Galileo) as a "nebula" (=cloud) even though it is not veiled in bright glowing gas like M42 in Orion.
Although, as we explain on our Trapzium page, the modern Orion nebula might actually be seen more clearly through a telescope less powerful than Galileo's, Peiresc's description of what he saw in Orion is extremely ambiguous, and whether it refers to M42 or not is quite unclear to us. Primarily, on the successive nights, he describes a pair of bright stars intermittently associated with some kind of cloud "in the middle" of Orion.
Among the things that make it unclear that Peiresc was describing M42 are:According to Seymour Chapin, inspired by Galileo's publication of Sidereus Nuncius, Peiresc sought to obtain a telescope, but was not able to do so until November 1610. He first managed to see the satellites of Jupiter (the most remarkable discovery announced in Sidereus Nuncius) on November 25, 1610, one day after his neighbor Joseph Gaultier. Since Peiresc's first journal entry cited by Bigourdan, describing a "cloud composed of two stars" seen "in the middle of Orion" on a night when the "sky was not clear" was recorded just a day later, on November 26, 1610, it seems conceivable to us that Peiresc may have simply been attempting to verify Galileo's observation of the Orion Nebula as he saw it pictured in Sidereus Nuncius (that is, the clustering of stars marking Orion's head). The succeeding journal entries, for December 1-10, 1610, may be describing how Peiresc saw this region sometimes resolved into a pair of stars and at other times as a formless blur. He may also have been literally recording his frustration with how terrestrial clouds in the sky interfered with his efforts to confirm Galileo's observations of the Head of Orion. The January 15th journal entry, describing the "nebula" in Cancer (the Beehive Cluster), reinforces our notion that Peiresc was systematically verifying the discoveries he saw reported in Sidereus Nuncius. Perhaps some reader will feel inspired to re-examine Peiresc's observing diary at Charpentras to get a better feel for his program and capabilities at the time.
As pointed out by Chapin, if Peiresc considered the intermittently visible "cloud" in the middle of Orion to be a new discovery he does not seem to have thought it important enough to mention to his associates, for there is no reference to such a discovery in the book-length Life of Peiresc written, shortly after Peiresc's untimely death, by his friend, protégé and fellow-astronomer Pierre Gassendi (we have not been able to track down the source of the apparent claim on the Galileo Project page that Peiresc's discovery in Orion was confirmed by Joseph Gaultier). It is possible, however, as Chapin also points out, that Peiresc may have considered such an observation to be of no practical importance. It is also possible, as we point out on our Trapezium, that since Galileo had just demonstrated that everything in the sky that appeared nebulous to the unaided human eye could be resolved into stars by the telescope, it would seem to follow that what appeared nebulous through the current telescopes could also be resolved into stars by more powerful telescopes. Although it turns out that the M42 nebula in Orion is of a different nature (primarily glowing gas that cannot be resolved into stars), in 1610 the observation of telescopic nebulae may not have seemed of great importance.
We have no idea how many others before Cysat may have noticed the glow of M42 through early telescopes, nor whether it was really as well known by 1619 as Cysat would seem to imply. But Galileo does not seem to be one of those who found M42 particularly noteworthy.
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Last modified: October 6, 2006