Bonilla Solar Transit Photographs

Theoretical Alignment

This case sits almost entirely outside the standard ETH/IDH framework: Bonilla never described a structured craft, controlled flight, or purposeful behavior — only irregular, drifting motion consistent with either a natural astronomical body or ordinary airborne animals. Its strongest theoretical alignment is Psycho-Social, not because any crowd hysteria occurred (this is a single, sober, credentialed observer), but because the case's entire modern "UFO" framing is a retroactive interpretive overlay: an ambiguous 1883 astronomical puzzle, quietly published and effectively forgotten for well over a century, was rediscovered and re-narrated by 21st-century media and ufological writers as "the first UFO photograph" only after the 2011 comet-fragment paper went viral. The underlying data itself — a solitary witness's photographic silhouettes with no radar, no structured shape, and no repeat appearance — offers no positive evidence for craft of extraterrestrial or interdimensional origin.

Background

José Árbol y Bonilla was born in the city of Zacatecas on February 5, 1853. He trained first as a topographical engineer at Zacatecas's Instituto Literario de García (today the Universidad Autónoma de Zacatecas), then won a state scholarship in 1873 from Governor Gabriel García to attend the Escuela de Minas in Mexico City, where he compressed a three-year civil-engineering curriculum into a single year. For that feat, President Sebastián Lerdo de Tejada personally awarded him the 1875 Premio al Mérito. Bonilla returned to Zacatecas to teach at his old Instituto while pursuing independent scientific study, and became the first director of the state's astronomical observatory when it opened on December 6, 1882 — described as the first major astronomical observatory in Mexico outside the capital.

In 1879 Bonilla traveled to Paris to study celestial photography at the Paris Observatory, and became a member of the scientific society of Camille Flammarion, the era's most prominent popularizer of astronomy in France. He returned to Zacatecas a trained astrophotographer at a moment of real institutional momentum: a telescope that arrived from France in 1882, a donation Bonilla himself arranged according to the University of Zacatecas, allowed Zacatecas to take part in observing the December 6, 1882 transit of Venus across the Sun — one of the 19th century's most closely watched international scientific events, timed to help refine the astronomical unit (the Earth–Sun distance). The observatory was inaugurated on the day of the transit, with Bonilla as director; Mexico News Daily places the observing point on Cerro de la Bufa, the hill overlooking Zacatecas's colonial center.

Eight months later, on the morning of August 12, 1883, Bonilla pointed that same instrument at the Sun for a routine sunspot check. What followed would occupy debate among astronomers, skeptics, and ufologists for the next 140-plus years. The broader scientific backdrop matters here in a way it rarely does for 20th-century UFO cases: 1883 predates radar, powered flight, radio, and any organized meteorological or astronomical monitoring network capable of independently cross-checking a solitary provincial observer's claim. Bonilla's only real-time corroboration option was the telegraph — and he used it, with a result that itself became part of the case's evidentiary record.

The institutional setting also matters. By 1883 Mexico was five years into the long presidency of Porfirio Díaz, whose government actively promoted scientific and technical modernization — new observatories, engineering schools, and international scientific participation such as the Venus-transit collaboration — as a matter of deliberate state policy, part of a broader positivist-influenced push to project Mexico as a scientifically capable nation. A provincial state government funding an astronomical-meteorological observatory, staffing it with a formally trained engineer sent abroad specifically to learn astrophotography, and equipping it with an imported French telescope was itself a product of this national moment, not an isolated local curiosity. That institutional backing is part of why Bonilla's account carries more evidentiary weight than a typical unaffiliated 19th-century witness: he was operating within, and reporting to, a real, internationally connected scientific infrastructure rather than acting alone and unaccountable.

Complete Timeline

Date	Event
Feb. 5, 1853	José Árbol y Bonilla is born in Zacatecas, Mexico.
1873–1875	Bonilla completes a three-year civil-engineering program at Mexico City's Escuela de Minas in one year on a state scholarship; President Sebastián Lerdo de Tejada awards him the 1875 Premio al Mérito.
1875	Bonilla returns to Zacatecas to teach topographical engineering.
1879	Bonilla travels to Paris to study celestial photography at the Paris Observatory and joins the scientific society of astronomer Camille Flammarion.
Dec. 6, 1882	The Zacatecas astronomical observatory opens, with Bonilla as director, on the day of the transit of Venus; its telescope had arrived from France that year.
Jan. 1883	Flammarion founds the monthly journal L'Astronomie in Paris — the publication that would carry Bonilla's account three years later.
Aug. 12, 1883, ~08:00	While checking the Sun for spots, Bonilla notices the first of many dark objects crossing the solar disk and begins exposing wet-collodion plates.
Aug. 12–13, 1883	Across roughly 25 hours (interrupted by cloud), Bonilla logs 3 hr 25 min of clear-sky viewing, counts 447 individual objects, and telegraphs observatories in Mexico City and Puebla to watch for the same phenomenon; neither reports seeing anything.
Jan. 1, 1886	L'Astronomie publishes Bonilla's account, submitted roughly two and a half years earlier, with an editorial note from Flammarion favoring birds, insects, or dust near the telescope's lens.
1911	Bonilla steps down from the Zacatecas observatory to direct Mexico City's National School of Arts and Crafts.
1920	Bonilla dies in Mexico City, having written the first modern cosmography text for Mexican schools.
Oct. 12, 2011	Héctor Javier Durand-Manterola, María de la Paz Ramos Lara, and Guadalupe Cordero Tercero of UNAM post an arXiv preprint proposing the objects were comet fragments that passed within roughly 538–8,062 km of Earth's surface.
Oct.–Nov. 2011	The hypothesis draws international press coverage (MIT Technology Review, Phys.org, AAAS) alongside detailed public rebuttals from astronomers Marco Langbroek and Phil Plait.
2015	Mexican newspapers Excelsior and El Universal revisit the case; the 1882 French telescope is still in use for public education at the University of Zacatecas's Manuel Ríos Herrera observatory, and a separate official observatory bears Bonilla's name.

The Observation

Multiple period and modern accounts agree on the essential shape of what happened, even where exact figures diverge slightly across secondary sources. On the morning of August 12, 1883, Bonilla was using the observatory's telescope to check the Sun's disk for sunspots — ordinary, routine solar-observation work for a 19th-century astronomer. Instead of, or alongside, sunspots, he began seeing small dark shapes drifting across the bright solar background: objects he described in his own account as "fuzzy" or "misty," several trailing what he called "dark tails," dark and roughly round or elongated when silhouetted against the disk, brightening briefly into visible highlights as they crossed the Sun's limb (edge) and left the disk. Bonilla, trained in Paris specifically in astrophotography, recognized the potential significance and exposed several wet-collodion photographic plates — a technically demanding process that required each glass plate to be sensitized, exposed, and developed while still wet. How many plates he made is uncertain: Mexico News Daily notes that he spoke of "several" and that there were at least three. The 447 figure is his count of objects, not of photographs.

The phenomenon did not appear continuously. Cloud cover repeatedly interrupted Bonilla's view across roughly a 25-hour span bridging August 12 and 13, and his own log distinguishes total elapsed time from actual clear-sky viewing time: by his own accounting, he had only about 3 hours and 25 minutes of unobstructed observation across the full period, and it was within that narrower window that he counted and individually logged 447 distinct objects crossing the disk. Some secondary sources report this as "over 400," "more than 300," or, in one case, extrapolate outward: the 2011 UNAM reanalysis projected that if objects had continued crossing at the same rate throughout the full, mostly cloud-obscured 25-hour period rather than only the clear intervals Bonilla could actually see, the true total might have approached 3,275 — a extrapolated estimate, not a second directly observed count, and one this case file treats as clearly distinct from the 447 Bonilla actually witnessed and recorded.

One secondary account summarizing Bonilla's own written description quotes him characterizing the objects as "dark-black and perfectly round," with some "more or less elongated when seen against the solar disc," before they "became bright images as they left" the Sun's edge — a specific, internally consistent visual description repeated, with only minor wording variation, across the handful of sources that quote his original account directly rather than paraphrasing it.

One detail repeated in secondary sources (Mexico News Daily among them) is that focusing on the Moon made the objects sharper, while focusing on the Sun blurred them, which suggests the objects were relatively near Earth. The detail should be handled with care. For a telescope, the Moon and the Sun are both effectively at infinite distance, so they share the same focus, and the Moon was below the horizon at Zacatecas during the morning observations (it rose in the early afternoon, about 66% lit, per NASA JPL Horizons). Taken at face value, the claim points to objects near the instrument. It is also consistent with the far more mundane explanation that the objects were simply much closer to the telescope than the Sun is — birds or insects near Zacatecas, not comet debris near the Moon's orbit.

Individual transit times across the solar disk were extremely brief. Bonilla estimated, without saying how he timed them, that each object took 1/3, 1/2 or 1 second to cross the roughly half-degree-wide solar disk, figures the 2011 team used directly — a detail load-bearing for every subsequent interpretation, mundane or exotic alike, since it is exactly the kind of rapid, near-field transit a bird or insect passing close to the objective lens would produce, and also the kind of transit an extremely fast-moving, extremely close astronomical body would produce. The ambiguity is baked into the data itself, which is precisely why the case has never been definitively closed in either direction.

Bonilla's Own Account and the Failed Corroboration Attempt

What distinguishes this case from the vast majority of historical sky-anomaly reports is that Bonilla did not simply record what he saw and move on — he actively tried, in real time, to get independent confirmation. Recognizing the potential scientific importance of what he was recording, he sent a telegraph message alerting observatories in Mexico City and in Puebla, asking them to look at the Sun and report whether they saw the same phenomenon. Both cities sit a few hundred kilometers from Zacatecas — well within range for a genuinely distant, extremely close-passing astronomical object to also be visible from a different parallax angle, and also well within range for a genuinely local, near-field phenomenon (birds, insects, atmospheric haze) to simply not be present over a different city on the same morning.

Neither Mexico City nor Puebla reported seeing anything unusual on the Sun that day. This negative result cuts in a specific, technical direction depending on which explanation one starts from. For the 2011 UNAM team, the failure of two other Mexican observatories to see the same objects became a load-bearing piece of supporting evidence: if the objects had genuinely been passing extremely close to Earth — hundreds to a few thousand kilometers up — then ordinary parallax alone could explain why observers a few hundred kilometers away, looking at the Sun from a measurably different angle, would see the objects silhouetted against a different, unaffected patch of the solar disk, or miss them from their sightline entirely. For skeptics, the same negative result cuts the opposite way: a genuinely fragmenting comet passing that close to Earth, moving at cometary or near-orbital velocities, would not plausibly stay confined to a debris corridor narrow enough that only one specific city's specific rooftop happened to catch it across more than 25 hours of Earth's own continuous rotation and orbital motion — a geometric objection independent astronomers would later develop in far more technical detail (see Mainstream Astronomical Skepticism, below).

Publication in L'Astronomie and Flammarion's Skepticism

Bonilla did not rush his findings to print. By his own account and by the timeline multiple sources confirm, he first sent his observations and photographic plates privately to Camille Flammarion in Paris — the astronomer under whose circle he had studied celestial photography four years earlier, and by 1883 the founder and editor of the brand-new journal L'Astronomie. Flammarion held the account for roughly two and a half years before finally publishing it in the January 1, 1886 issue.

Flammarion's own editorial judgment, appended directly to Bonilla's report, was skeptical: he suggested the most likely explanation was that Bonilla had photographed birds, insects, or dust passing close to his telescope's objective lens rather than anything genuinely in space near the Sun. Flammarion had at least the photograph reproduced in the journal before him, though how many of Bonilla's plates he saw is not documented. According to the 2011 UNAM authors, Bonilla himself reported his observations "without providing a hypothesis," and the editor's suggestion was offered because he "could not find a suitable explanation." The case therefore went into print with an observation but no settled interpretation from either the observer or his editor.

After its 1886 appearance in a French astronomical journal with a modest circulation, the case drew little sustained attention for well over a century. It was occasionally mentioned in later UFO-literature surveys of pre-20th-century "aerial phenomena," but never became a headline case the way 20th-century sightings with radar or multiple named military witnesses did — there was, after all, no structured craft, no repeat appearance, and by the time organized ufology emerged in the late 1940s the case was already six decades old and largely confined to specialist astronomical-history circles.

The 2011 Comet-Fragment Hypothesis

That changed in October 2011, when three scientists at Mexico's Universidad Nacional Autónoma de México (UNAM) — space physicist Héctor Javier Durand-Manterola, science historian María de la Paz Ramos Lara, and geophysicist Guadalupe Cordero Tercero — posted a preprint on arXiv titled "Interpretation of the observations made in 1883 in Zacatecas (Mexico): A fragmented Comet that nearly hits the Earth." Their central claim: the 447 objects Bonilla documented were fragments of a comet that had recently broken apart and was passing extremely close to Earth — not merely close in astronomical terms, but close enough that the encounter would have counted among the most significant near-misses in recorded history had any of the fragments actually struck the planet.

Their methodology worked from the observational data Bonilla himself had painstakingly logged: the timing, apparent angular size, and transit duration of individual objects crossing the solar disk, combined with the negative result from Mexico City and Puebla. Using those transit times and the assumption that the fragments' true distance from Earth could be bounded by the fact that nearby cities failed to see them (an argument from parallax and limited visibility geometry), the team calculated the fragments passed at an altitude of roughly 538 to 8,062 kilometers above Earth's surface — some estimates from secondary press coverage of the same paper cited ranges up to several tens of thousands of kilometers, reflecting the wide uncertainty bands inherent in reconstructing 128-year-old naked-eye/photographic timing data. From the same transit-time data, they derived individual fragment dimensions on the order of 46 to 795 meters wide and 68 to 1,022 meters long, with individual masses estimated between roughly 5.58×10&sup8; and 2.5×10¹² kilograms. Extrapolating to a single parent body, they proposed an original comet mass ranging from about 1.83×10¹² to 8.19×10¹&sup5; kilograms — a range whose upper bound would make the parent comet more massive than Halley's Comet itself, and whose implications, had the debris struck Earth instead of missing it, the authors themselves framed in stark terms: the equivalent of thousands of Tunguska-scale explosions occurring within a 25-hour window, a scenario some coverage of the paper described as being on the scale of a potential mass-extinction event.

The UNAM team's argument for taking Bonilla seriously rested heavily on his own credentials and methodology: a Paris-trained astrophotographer, personally directing a functioning observatory, who logged a count of 447 objects, transit-time estimates, and photographs rather than a single ambiguous account. The paper itself does not argue against the birds-and-insects explanation in any detail; it explains the editor's choice by noting that in 1883 only two comet fragmentations had been observed, and it suggests one of that year's known comets, 1883 II (Pons–Brooks) or 1883 I (Brooks–Swift), as a possible parent, citing the northeast-to-southwest slant (about 43°) of the tracks in Bonilla's figure. Some secondary science coverage additionally described the hypothesis in terms of a possible Kreutz-family sungrazing comet, though this specific sub-classification does not appear explicit in the original 2011 preprint itself and should be read as a later media gloss rather than the authors' own stated claim.

Notably, the 2011 paper has circulated only as an arXiv preprint; this case file's research did not locate evidence that it was ever formally peer-reviewed and published in a standard astronomy journal in the years since. That does not automatically invalidate its reasoning, but it does mean the hypothesis has never passed the kind of independent editorial and referee scrutiny that would normally be expected before an extraordinary historical near-miss claim of this scale is treated as an established finding — a gap that becomes more significant in light of the specific technical rebuttals detailed below.

Mainstream Astronomical Skepticism

The comet-fragment hypothesis drew serious, technically specific pushback from working astronomers almost immediately, distinguishing this from a case where "skepticism" means simple dismissal. Dutch satellite tracker and meteor observer Marco Langbroek, writing on his SatTrackCam Leiden blog on October 17, 2011, directly challenged the parallax reasoning at the heart of the UNAM paper. He pointed out that during the 3 h 25 min of observation the Earth moved about 370,000 km along its orbit and its surface rotated a considerable distance. A stream seen from Zacatecas over that time would therefore have to be thousands of kilometers wide and "really should have been seen from other places as well," which he called "deadly" to the restricted-visibility argument. He also noted that the "fuzzy" appearance suggests out-of-focus objects close to the instrument, "most likely within the telescope system," and called the comet story "far-fetched and very unlikely."

American astronomer and science writer Phil Plait, writing on his widely read "Bad Astronomy" platform (hosted at the time by Discover magazine), raised several additional, more physical objections. Comets that fragment do not confine their debris to a tight cluster: "even when intact, the material surrounding a comet can be tens or even hundreds of thousands of kilometers across," Plait noted, making it hard to reconcile a genuinely fragmenting body with debris packed into only a few thousand kilometers of altitude. He further pointed out that the objects would have been stretched along "a path that was a million km long at least," yet seen by only one observatory — essentially the same geometric objection Langbroek raised, arrived at independently the same day. Most damagingly, Plait highlighted the complete absence of any accompanying meteor activity: a genuine, disintegrating, near-Earth cometary mass of the size proposed should have produced a meteor shower "practically biblical in size," and no such display is recorded. No documented fragmentation of the parent candidates the UNAM authors floated has surfaced to support the hypothesis. Plait named no single preferred explanation, suggesting "flocks of birds for example, or an odd atmospheric phenomenon," while allowing that "it's perfectly reasonable to think he saw something," and concluded the comet idea had "too many flaws."

Science writer Brian Dodson, summarizing the debate in an AAAS Scientia piece of November 2, 2011, reached a similarly cautious conclusion: despite Bonilla's excellent reputation among astronomers and an observatory suitably equipped for solar work, the cause "remains a mystery," because accepting the comet hypothesis would require more data than Bonilla provided. UFO researcher and author Kevin Randle, discussing the case on his own blog in 2015, likewise described the comet hypothesis as "a reasonable suggestion, but one, at the moment, that is not proven, just likely" — explicitly declining to endorse it outright even while treating it more charitably than Plait or Langbroek did. Commenters on Randle's post raised further objections: David Rudiak noted that "any comet would have been traveling at about 20 miles/sec" and that the August Perseids come from comet Swift–Tuttle, which was not near Earth in 1883. One commenter proposed that an Aten-class near-Earth asteroid — a class of small bodies orbiting entirely within Earth's own orbit — would better fit the observed motion characteristics and ecliptic-plane trajectory than a classic long-period comet, though this remains an informal suggestion raised in blog-comment discussion rather than a peer-reviewed alternative model, and this case file did not locate any published follow-up work developing it further.

The Birds, Insects, and Dust Hypothesis

Set against the comet hypothesis, the case's original 1886 explanation — Flammarion's proposal that Bonilla photographed birds, insects, or dust close to his telescope's objective lens — has aged, on balance, at least as well as its modern rival, and in several mainstream astronomers' assessments (Plait's among them) somewhat better. The core appeal of this explanation is almost entirely negative evidence: the total absence of any corroboration from two nearby observatories that were specifically alerted and asked to look, the total absence of any meteor shower or fireball activity that a genuine close-passing comet mass should have produced, and the brief (one-third to one second) individual transit times, which are fully consistent with a bird or flying insect passing near a telescope's field of view rather than requiring an exotic astronomical explanation at all. This is, in fact, essentially the same phenomenon amateur solar and lunar photographers still document today: birds and aircraft passing near enough to a telephoto or telescope-mounted lens to appear as sharp, fast-moving silhouettes against the Sun or Moon, frequently interpreted by inexperienced observers as much larger or much more distant than they actually are.

The hypothesis is not without its own weaknesses, which is precisely why this case remains open rather than closed in the mundane direction. Bonilla was not an inexperienced observer; he was a Paris-trained astrophotographer, and the explanation requires him to have misread hundreds of near-lens intrusions across more than three hours of deliberate work — a real, if not conclusive, argument in the other direction. Neither side of this debate has produced a smoking-gun piece of evidence (a recovered bird carcass, a documented local insect swarm, a positively identified comet) that would move the case from "most plausible mundane candidate" to "proven mundane explanation."

The Zacatecas Observatory Today

Bonilla's instrument survives in Zacatecas. A 2015 Notimex report carried by Excelsior, quoting Zacatecas Astronomy Society president Alejandro Muñoz and Gloria Eleana Espinoza Valadez, for 11 years in charge of the telescope, said the equatorial telescope that arrived from France in 1882 is still in use. It is kept at the Manuel Ríos Herrera observatory of the Universidad Autónoma de Zacatecas's topographic-engineering unit, keeps its original brass parts, and is open to the public Monday through Friday from 8 to 10 p.m., mainly for educational visits. The same coverage noted that present-day Zacatecas hosts two of Mexico's officially recognized astronomical observatories — the Manuel Ríos Herrera Observatory at the Universidad Autónoma de Zacatecas and the José Árbol y Bonilla Observatory itself — a legacy this single 1883 morning, whatever its ultimate explanation, helped put on the map of Mexican scientific history a full century before ufological interest in the case began.

Key Witnesses

The Five Observables Assessment

The Five Observables framework is applied to the performance characteristics reported in this case:

Assessment: This case cannot be scored cleanly against the Five Observables because its interpretation is precisely what's in dispute. If the objects were genuinely near-Earth cometary fragments as the 2011 UNAM paper proposes, their implied real velocity (tens of kilometers per second) would register as speculatively hypersonic; if they were birds or insects near the lens, no such velocity is implied at all, since their apparent speed across a magnified telescopic field says nothing about their true airspeed. The same ambiguity applies to Low Observability: the objects were invisible to two nearby, specifically alerted observatories, which is consistent either with a genuinely narrow, close-passing debris corridor or with an entirely mundane, purely local phenomenon that simply wasn't present over a different city that same morning. No instant acceleration, structured maneuvering, or trans-medium behavior of any kind was ever reported, which argues against a controlled or piloted craft under either interpretation.

Evidence Assessment

Why "Disputed"

This case earns a DISPUTED classification because it genuinely resists resolution in either direction, for reasons that have only sharpened with 21st-century scrutiny rather than settling the matter. On one hand, Bonilla was a real, credentialed, methodologically careful observer who produced an unusually rigorous data set for his era — a precise count, exposed photographic plates, and a documented, contemporaneous attempt at independent corroboration — and no one has ever positively identified the specific mundane cause (a particular bird species, a specific insect swarm, a named comet) that would definitively close the case. On the other hand, the single most serious modern attempt to treat the objects as genuinely anomalous — the 2011 UNAM comet-fragment hypothesis — has been met with specific, technically grounded objections from independent astronomers that this case file's research could not find any published rebuttal to: no meteor shower where one should exist, no documented fragmentation of any candidate parent comet, and a geometric problem reconciling "close enough to be invisible from 300 km away" with "narrow enough that only one observatory saw it" across more than a day of Earth's own rotation and orbital motion. A case with a single uncorroborated witness, an explicitly disputed 2011 preprint as its leading anomalous explanation, and a conventional explanation (birds/insects/dust) that itself has never been definitively confirmed sits squarely in Disputed territory: too well-documented and too technically serious on both sides to dismiss outright, and too short on independent corroboration or positive physical proof to rate as Credible or Verified.

Sensor & Instrumentation Detection Profile

The only instrumentation involved was the observatory's refracting telescope (the instrument that arrived from France in 1882) and several wet-collodion glass photographic plates, reportedly exposed at about 1/100 second (per Wikipedia). No radar, radio, or any other detection system existed in 1883 to independently register the event; the telegraph functioned only as a same-day communication tool for requesting a second visual observation, not as an instrument capable of detecting the objects itself. This remains, even 140 years later, one of the earliest attempts anywhere to document a solar-disk aerial anomaly through instrumented (photographic) means rather than eyewitness testimony alone.

Environmental & Geospatial Context

Zacatecas sits on the southern edge of Mexico's high central plateau; the observatory itself, atop Cerro de la Bufa overlooking the city's colonial center, sits at high altitude in a semi-arid climate that local astronomers have long credited with unusually clear, stable seeing conditions (the city stands at roughly 2,400 meters). Bonilla's total observation time across August 12 and 13, 1883 was 3 hours 25 minutes, in which the 447 counted objects were logged; the UNAM paper's extrapolation assumes the stream continued from 8 a.m. on the 12th to 9 a.m. on the 13th. No meteorological instrumentation beyond direct human observation existed at the site to record more granular atmospheric data from the event.

Observer Credibility & Occupational Profile

The case rests entirely on one observer's credibility, which is unusually strong for a single-witness account: José Bonilla was a state-scholarship civil engineer, a Paris-trained astrophotographer, the founding director of a real, functioning government observatory, and later the director of a national vocational school in Mexico City — a career trajectory built entirely on technical credibility rather than showmanship or self-promotion. He published nothing sensationalized about the case himself; his account went through Camille Flammarion's own editorial vetting before reaching print, and he continued a distinguished, unremarkable scientific and administrative career for more than three decades afterward, including authoring Mexico's first modern cosmography textbook, with no evidence of seeking further attention from the 1883 event. Working against this strength is the case's structural weakness: he is the only witness, and his own attempt to secure a second one, by telegraph, came back empty.

Physical & Material Assays

The only physical evidence ever associated with this case is Bonilla's series of wet-collodion photographic plates, exposed across the two observation days. No modern physical or chemical testing has ever been possible because the original glass plates do not survive; every analysis conducted since 1886, including the 2011 UNAM reanalysis, has worked exclusively from the printed reproductions that accompanied the L'Astronomie publication and from Bonilla's own written measurements and descriptions, not from the source negatives themselves. See Material Analysis, below, for full detail on what those surviving reproductions do and do not allow researchers to determine.

Historical Precedents & Archive Matches

The Bonilla case sits within a broader 19th-century pattern of ambiguous aerial phenomena reported across the Americas in the decades bracketing it — a pattern this site catalogs elsewhere, including the Maracaibo UFO Sighting just three years later in Venezuela, and the far more contested Sonora Aero Club claims of secret airship-building in 1850s California, reconstructed decades after the fact from a single artist's account. It also anticipates, in a specifically Mexican context, the country's next major solar-adjacent aerial phenomenon more than a century later: the 1991 Mexico City Eclipse UFO Wave, in which an object was photographed near the eclipsed Sun by numerous independent observers — a case with the multi-witness corroboration this 1883 case conspicuously lacks, and one that helped launch the modern Mexican civilian ufology movement Bonilla's own case would later be absorbed into, retroactively, as an early historical precedent.

Material Analysis

The entirety of this case's physical evidence is a handful of wet-collodion photographic plates made across August 12–13, 1883 (Bonilla spoke of "several"), of which only printed reproductions — produced for the 1886 L'Astronomie publication — are known to survive today. This is a genuinely unusual level of documentation for a pre-20th-century aerial anomaly report, most of which rely on written testimony alone, but it is also a fundamentally limited evidentiary base: no original negative has been located by any researcher consulted in this case file's research, meaning every modern claim about the objects' apparent size, shape, or motion derives from period print reproductions and Bonilla's own written transit-time measurements, not from direct re-examination of the source photographic data.

The Wet-Collodion Process and What It Could (and Could Not) Capture

The wet-collodion (wet-plate) photographic process dominant in 1883 required a glass plate to be coated with a light-sensitive collodion emulsion, exposed while still wet, and developed within minutes — meaning Bonilla needed a functioning darkroom set up at or immediately adjacent to the telescope itself to produce his exposures. One secondary source specifically cites exposure times on the order of 1/100 of a second per plate, fast enough to freeze a rapidly moving near-field object (a bird or insect) as a sharp silhouette, but also fast enough to capture a genuinely distant, extremely fast-moving body without significant motion blur. The technique itself, in other words, cannot by itself distinguish between the competing hypotheses; it only establishes that Bonilla had the real technical capability to produce the photographic record his written account describes, which lends credibility to the account's basic mechanics even though it says nothing about what, specifically, the plates depicted.

Why the Original Plates No Longer Exist

Nineteenth-century glass photographic plates were fragile, chemically unstable over long storage periods, and rarely prioritized for preservation once a printed reproduction existed for publication purposes. Bonilla's original plates appear to have been lost or destroyed at some point in the 140-plus years since 1883 — a loss common to the vast majority of 19th-century scientific glass-plate collections worldwide, not evidence of any particular suppression or negligence specific to this case. The practical consequence for modern researchers is the same regardless of cause: no electron microscopy, spectral analysis, or high-resolution digital re-scan of the actual exposed emulsion has ever been possible, and none will be, absent the rediscovery of an original plate in some uncatalogued archive.

The Conventional Explanation Candidate

Three genuinely distinct candidate explanations have been seriously proposed for this case since 1886, and this case file evaluates each on its own merits rather than collapsing them into a single verdict.

Migrating Birds, Insects, or Debris Near the Telescope's Objective Lens

This is the case's original explanation, proposed by Camille Flammarion in the very 1886 issue of L'Astronomie that first published Bonilla's account, and it remains the explanation favored by the most prominent modern astronomer to weigh in publicly, Phil Plait. It deserves serious evaluation because it requires no exotic astronomical event, fits the brief individual transit times Bonilla estimated, and directly explains the total absence of corroboration from Mexico City and Puebla: a local flock of birds or insect swarm over Zacatecas has no reason to also be present, at the same moment, over cities several hundred kilometers away. Its principal weakness is that Bonilla, a trained astrophotographer, would have needed to misread hundreds of near-lens intrusions across more than three hours of deliberate work — a real, if not fatal, objection.

Fragmented Comet Passing Extremely Close to Earth

Proposed in the 2011 UNAM preprint by Durand-Manterola, Ramos Lara, and Cordero Tercero, this hypothesis treats Bonilla's transit-time data as genuine orbital-mechanics evidence and derives a self-consistent, if wide-ranging, set of distance, size, and mass estimates for a disintegrating cometary body. It deserves serious evaluation because it was produced by credentialed academic scientists working quantitatively from Bonilla's own primary data, rather than dismissing or embellishing it, and because it offers a positive, falsifiable physical model rather than merely asserting that "something happened." Its central weaknesses, raised independently by Marco Langbroek and Phil Plait, are specific and unaddressed as of this case file's research: the geometry required to make the fragments invisible from Mexico City and Puebla while visible from Zacatecas implies a debris corridor difficult to reconcile with a genuinely fragmenting comet's typical spread; no meteor shower or unusual fireball activity of the scale the proposed mass should have produced has ever been documented; and no documented fragmentation of the candidate parents the authors floated (1883 I and 1883 II) has been found. This file also found no peer-reviewed journal version of the arXiv paper.

A Genuine, Never-Identified Aerial or Near-Earth Phenomenon

Some UFO literature treats the case, on the strength of its enduring lack of full resolution, as evidence of a genuinely unexplained aerial phenomenon in its own right, sometimes framing it as "the first UFO photograph." This case file rates this as the weakest-evidenced of the three candidates: it is defined almost entirely by the shortcomings of the other two explanations rather than by any positive evidence of its own, and even most serious treatments of the case (including the UNAM paper) never describe a structured craft, controlled maneuvering, or any purposeful behavior — only irregular, drifting motion. Genuine scientific uncertainty about which mundane or semi-mundane explanation is correct is not, by itself, positive evidence of a structured, piloted, or otherwise deliberately controlled object.

Related Cases

Further Reading — Recommended Literature

DISCLOSURE: Some links above are affiliate links. If you purchase through them, OverClassified receives a small commission at no additional cost to you. This helps support independent research.

Essential Viewing

Sources

• Durand-Manterola, H.J., Ramos Lara, M.P., Cordero Tercero, G. "Interpretation of the observations made in 1883 in Zacatecas (Mexico): A fragmented Comet that nearly hits the Earth." arXiv:1110.2798, Oct. 12, 2011. arxiv.org
• "Bonilla observation." Wikipedia. en.wikipedia.org
• "José Bonilla (astronomer)." Wikipedia. en.wikipedia.org
• "Observación de Bonilla." Wikipedia (Spanish). es.wikipedia.org
• Choi, Charles Q. "Billion-Ton Comet May Have Missed Earth by a Few Hundred Kilometers in 1883." MIT Technology Review, Oct. 17, 2011. technologyreview.com
• "Mexican astronomers suggest Bonilla sighting might have been a very close comet breaking up." Phys.org, Oct. 2011. phys.org
• Dodson, Brian. "Did a comet almost cause Doomsday in 1883?" AAAS Scientia, Nov. 2, 2011. aaas.org
• Plait, Phil. "Did a fragmenting comet nearly hit the Earth in 1883? Color me very skeptical." Discover Magazine (Bad Astronomy), 2011. discovermagazine.com
• "Was the 'First Photographed UFO' a Comet?" Universe Today. universetoday.com
• "Reanalysis of 1883 Observations Suggests a Billion-Ton Comet Buzzed Earth." Space Safety Magazine. spacesafetymagazine.com
• "The day the world nearly ended and nobody — except one Mexican scientist — noticed." Mexico News Daily. mexiconewsdaily.com
• Minjarez, Emerio. "The Bonilla Observation: A Puzzling Event in the History of Astronomy." Medium. medium.com
• Randle, Kevin. "Bonilla's Comet." A Different Perspective, May 2015. kevinrandle.blogspot.com
• "File:Jose Bonilla UFO observation 12 August 1883.jpg." Wikimedia Commons. commons.wikimedia.org
• "Primeras fotos de 'OVNIS' fueron captadas en Zacatecas en 1883." Excelsior, Oct. 8, 2015. excelsior.com.mx
• "Observatorio de Zacatecas tomó primeras fotos de OVNIS." El Universal, Oct. 8, 2015. eluniversal.com.mx
• NASA Jet Propulsion Laboratory. "Center for Near-Earth Object Studies (CNEOS)." cneos.jpl.nasa.gov
• Langbroek, Marco. "OT: the 1883 Zacatecas observation of a ‘comet’," SatTrackCam Leiden, Oct. 17, 2011. sattrackcam.blogspot.com
• NASA JPL Horizons, Moon (301) position and illumination, Zacatecas (22.77°N 102.58°W), 12–13 Aug. 1883 UTC. ssd.jpl.nasa.gov

Corrections (October 2026)

An October 2026 fact-check compared this page with the full text of the 2011 UNAM preprint (arXiv:1110.2798), Marco Langbroek's and Phil Plait's posts of October 17, 2011, Brian Dodson's AAAS piece, Kevin Randle's 2015 post and its comments, the 2015 Notimex/Excelsior report, Mexico News Daily, and NASA JPL Horizons. The largest error: the page described "447 wet-collodion photographic exposures." The 447 figure is Bonilla's count of objects. He made several plates (at least three by one account), and one image was reproduced in L'Astronomie. The page also had Bonilla disputing Flammarion's birds-and-insects suggestion, and the UNAM paper arguing it "doubtful" that he mistook insects. Neither is in the sources; the paper says Bonilla offered no hypothesis.

Following this review, the rating was changed from Disputed 39 to Disputed 33 (October 28, 2026), because the higher rating had rested partly on claims corrected or removed above.

Removed or corrected quotations. Langbroek's "at least 20 Earth diameters wide" is not in his post; his actual argument is now given. Plait's "Perseid… not a fine one by any means" line and his supposed statement that Bonilla "photographed" something do not appear in his post. Dodson's "stellar reputation and properly equipped facility" is not his wording. Other corrections: the transit times were Bonilla's estimates of 1/3 to 1 second, not "well under a second." The observatory opened on December 6, 1882 (a separate 1878 founding date was unsourced). The surviving 1882 French telescope is at the University of Zacatecas's Manuel Ríos Herrera observatory, not in an observatory "bearing Bonilla's name." The 1920 death date no longer gives a day. The UNAM authors did float candidate parent comets (1883 I and II). The Moon-focusing anecdote is now attributed and qualified: per Horizons, the Moon was below the horizon during the morning observations.