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. Instead of sunspots he saw something he did not expect: a procession of dark objects, small and fuzzy-edged, crossing the solar disk in loose groups, at different speeds and trailing a kind of wake. Over about three and a half hours spread across August 12 and 13 he counted 283 objects the first day and 164 the second —more than 440 in total— and had the presence of mind to photograph them with the wet collodion plate technique, the cutting edge of astronomical photography of his day. The images showed elongated, blurry silhouettes projected on the Sun and, according to Bonilla, also off it against the sky. He proposed no explanation: he recorded, measured and photographed, which is exactly what an observatory is asked to do.

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 only in 1885 (circulating into January 1886), more than two years after the observation. The journal's editor, without having been in Zacatecas, ventured that they might be high-altitude migrating birds or insects crossing very close to the lens —a hypothesis Bonilla never adopted, because it did not fit the behavior nor the fact that the objects seemed to transit the solar disk. 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, today lost or not preserved in usable condition. 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 the oldest piece in the corpus that 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 a peer-reviewed scientific 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 if the most probable explanation is prosaic, 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', which no one believed, 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 original plates do not survive in usable form, so the supposed closure depends on reconstructions from the published numbers. The case thus stands as Tier B —impeccable documentation, but an unrecoverable object with 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'. For a corpus that separates the strength of the evidence 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.