Mexico.Bonilla observation · Zacatecas Observatory

On August 12, 1883, José Arbol y Bonilla (physician, engineer and director of the modest Zacatecas Observatory, on Mexico's central highlands) pointed his telescope at the Sun to study sunspot activity. At about eight in the morning, while drawing the spots, he saw 'a small luminous body' enter the field and cross the disk like a nearly circular shadow, then another, and another: in two hours he counted 283; after an interruption by clouds, another 48 in forty minutes as the Sun crossed the meridian, and on August 13, in 45 minutes of clear sky, 116 more, 447 in all. All moved from west to east, took between a third of a second and a second to cross the disk, sometimes one or two passed and sometimes fifteen or twenty almost at once; on the Sun they looked black and opaque, and off the disk, luminous and with 'bright trails'. He swapped in a photographic objective and took several wet collodion plates while an assistant counted the bodies; on them the bodies, which looked round to the eye, showed irregular shapes. Bonilla did propose a reading: he had telegraphed the Mexico City and Puebla observatories, which saw nothing, and since when he focused his instruments on the bodies only the Moon came almost into focus, he concluded they were 'at a lesser distance than the Moon' and that their large parallax threw them off the solar disk as seen from those cities.

Bonilla sent his notes and plates to Camille Flammarion, the French astronomer and popularizer who founded the journal 'L'Astronomie'. The work was published there in the September 1885 issue (volume IV), more than two years after the observation. The editorial note judged it 'very interesting, but not easy to explain': it thought of the August shooting stars, but found it odd that nothing was seen in Mexico City or Puebla, and leaned towards 'birds, insects or upper dust', in any case bodies 'belonging to our atmosphere', a reading different from Bonilla's. In January 1886 the journal printed two replies: J. Herschel pointed to similar phenomena described in the Monthly Notices of March 1870, and H. Bruguière reported that in Marseille, in April 1883, he had watched small, ill-defined bodies crossing the Sun in the same west-to-east direction for more than twenty-four hours; the editors concluded that both observers had seen identical phenomena, of a cause hard to guess, probably very close to the Earth. For over a century the episode remained an archival curiosity: the 'first photograph of a UFO', cited in ufological literature but without a scientific closure.

In October 2011, three researchers from UNAM's Institute of Geophysics and Center for Applied Sciences (Héctor Manterola, María de la Paz Ramos Lara and Guadalupe Cordero) published a preprint with a remarkable reinterpretation. Taking the figures, timings and the lack of parallax between what Zacatecas would have seen and other observatories, they proposed that Bonilla observed the fragments of a comet that had disintegrated and whose pieces passed extremely close to Earth (by their estimate, between a few hundred and a few thousand kilometers) which would explain both the apparent size and why no other observatory reported the transit (they were too close to be seen from another latitude). If correct, Bonilla's observation would not be an unidentified aerial phenomenon but the accidental record of a catastrophic-risk event: a comet of perhaps a billion tons, fragmented, grazing the planet. The hypothesis is elegant but disputed: it rests on assumptions about distance and number of fragments that cannot be verified against the original plates, which the sources consulted do not locate. Thus the object remains formally open: top-tier period documentation, a strong but unproven natural explanation, and no surviving plate to close the case.

It matters as an early piece that already meets the methodological ideal the rest of the catalogue pursues: an observation with an instrument (telescope), a physical record (photographic plate), precise date and time, a quantitative count and publication in an astronomy journal. In 1883, before the word 'UFO' existed, an observatory did exactly what a modern program like AAWSAP tried to do a century later: measure instead of narrate. That is why, even though prosaic explanations have been proposed, the case is valuable: it shows the problem is not a lack of rigor in the witnesses but the intrinsic difficulty of closing a transient phenomenon of which only the record, not the object, survives.

Its second lesson is about how science digests the anomalous over time. For 128 years the observation hung between two bad options: the editorial guess of 'birds or insects', and the ufological appropriation as 'the first photographed UFO', which explained nothing either. Only in 2011 did a serious, falsifiable natural hypothesis (cometary fragmentation with a close pass) give it a scientific reading, at the price of turning the case into a near-miss that would have gone unnoticed. That hypothesis, however, is not proven: the sources consulted do not locate the original plates, so the supposed closure depends on reconstructions from the published numbers. The case thus stands with impeccable documentation, but with an unrecoverable object and no modern independent verification, and as a reminder of two things at once: that most of the anomalous turns out to have a natural explanation when there is data, and that 'having a plausible explanation' is not the same as 'being proven'. Once the strength of the evidence is separated from the nature of the object, Bonilla is the clean example of strong evidence about an object that was probably mundane but was never confirmed.