José Bonilla was not looking for catastrophe.
The director of the Zacatecas Observatory in central Mexico was conducting routine solar observations on the morning of August 12, 1883, when objects began crossing the solar disk. He counted them as they passed. He photographed as many as his camera would capture. By the time the observation session ended on August 13, he had recorded 447 separate objects transiting the face of the Sun.
He reported the observations to the French astronomical journal L’Astronomie, which published a note and one of his photographs in 1886. The journal’s editors proposed the objects might be birds or insects passing close to the telescope’s objective lens, which would explain why they appeared against the solar disk and why no other observatory reported seeing them. Bonilla disagreed with this explanation but could not provide a definitive alternative.
The photographs were preserved in the Zacatecas Observatory archive. The observation was noted in the astronomical history literature as a curiosity without explanation. For 128 years, the character of whatever Bonilla saw remained undetermined.
In 2011, a team of astronomers at the National Autonomous University of Mexico, led by Héctor Javier Durand of the Geophysical Institute and including María de la Paz Ramos and Guadalupe Cordero, published an arXiv paper analyzing Bonilla’s original photographs using modern astronomical methodology. Their conclusion was startling and disturbing: Bonilla had photographed a fragmented comet passing extremely close to Earth, whose individual fragments were the objects crossing the solar disk, and whose calculated closest approach distance was between 538 and 8,000 kilometers from the planet’s surface.
Whether their analysis is correct determines whether August 12-13, 1883 was one of the closest planetary near-misses in recorded human history, or a misidentified atmospheric or biological phenomenon that produced an intriguing but ultimately mundane historical astronomical note.
The Parallax Argument
The UNAM team’s central methodological argument is elegant and specific: the objects Bonilla photographed were only visible from Zacatecas.
When astronomers in the nineteenth century observed objects crossing the solar disk, they typically reported them to other observatories to allow parallax measurements. Parallax, the apparent shift in position of an object against a distant background as seen from two different geographic locations, allows the distance of the foreground object to be calculated with precision. The further away the object is, the smaller the apparent shift; the closer the object, the larger the shift.
Bonilla reported his observations to other observatories. None confirmed seeing the objects during the same period. This absence of independent confirmation is typically interpreted as meaning the objects did not exist or were local artifacts, which supports the birds-and-insects hypothesis. The UNAM team’s reinterpretation inverts this logic: if the objects were extremely close to Earth, they would subtend an extremely large parallax angle against the solar disk as seen from different geographic locations, making them invisible against the solar disk from any observatory more than a few hundred kilometers from Zacatecas.
An object at a distance of 8,000 kilometers from Earth’s surface would appear shifted against the solar background by an angle that would place it outside the solar disk as seen from an observatory in a different geographic region. The objects would be visible against the sky but not against the sun, making their detection much less likely in an era before systematic all-sky monitoring. An object at 538 kilometers, the lower bound of the UNAM estimate, would be entirely invisible against the solar disk from any other location on Earth’s surface.
The absence of confirmation from other observatories, which seemed to argue against the reality of the objects, is reinterpreted by the UNAM team as the precise parallax signature expected from objects at the calculated distances. The argument is internally consistent and physically grounded.
The Calculated Near-Miss
The UNAM team’s calculations, based on the angular velocity of the objects across the solar disk, their apparent sizes, and the parallax constraint, produced physical parameters for the objects and their closest approach.
Object sizes: between 46 and 795 meters in width and between 68 and 1,222 meters in length. These dimensions are consistent with cometary fragments, which range from meters to kilometers in size depending on the parent comet’s original dimensions and the degree of fragmentation.
Closest approach distance: between 538 and 8,000 kilometers from Earth’s surface. For comparison, the Moon orbits at approximately 384,400 kilometers. The International Space Station orbits at approximately 400 kilometers. The UNAM team’s lower bound of 538 kilometers would place the objects within the orbital zone of low Earth orbit satellites.
Number of fragments: approximately 447 recorded objects, implying a parent comet that had disintegrated into hundreds of individual fragments before closest approach. The disintegration pattern is consistent with well recorded cometary behavior: Comet Shoemaker-Levy 9 fragmented into 21 confirmed pieces before its 1994 Jupiter impact. A comet experiencing tidal disruption during a close solar or planetary approach characteristically produces exactly the kind of fragment cloud that Bonilla’s photographs show.
The energy calculation: if any of the larger fragments, those in the range of 795 meters to 1,222 meters, had impacted Earth, the impact energy would have been comparable to the event that ended the Cretaceous period 66 million years ago. The UNAM team’s comparison to 3,275 Tunguskan events is calibrated against the 1908 Tunguska explosion in Siberia, itself estimated at approximately 10-15 megatons. Scaling to 3,275 Tunguska equivalents produces an impact energy in the range of 30,000-50,000 megatons, comparable to the largest estimates for the Chicxulub impactor’s regional energy deposition.
The Durand team described their work as a plausible theory of a fact recorded by a Mexican in 1883. The photographs are in the archive. The calculation is in the arXiv paper. The near-miss, if the theory is correct, occurred during the morning hours of August 12, 1883, while most of Zacatecas was asleep.
1883 and the Two Catastrophes
The timing of Bonilla’s observations introduces one of the most remarkable coincidences in the modern historical record: within two weeks of August 12-13, 1883, Earth experienced both a potential comet near-miss of civilization-ending scale and the most catastrophic volcanic eruption in the modern instrumental period.
Krakatoa’s August 27, 1883 eruption, covered in exhaustive detail in the Krakatoa piece in this library, produced a 200-megaton equivalent explosion, a tsunami reaching 30 meters that killed 36,417 people, a pressure wave that circled the globe seven times, and a stratospheric aerosol injection that dropped global temperatures for five years.
Whether the temporal proximity of the Bonillan observation and the Krakatoa eruption reflects coincidence, a causal relationship whose mechanism is not immediately obvious, or is simply the way that 1883 happened to be a year of concentrated planetary hazard, is a question whose answer the available evidence does not establish.
The causal relationship hypothesis, while not supported by any known mechanism, is not physically impossible: a cometary fragment entering the upper atmosphere without ground impact could in principle deposit energy and material in ways that interact with volcanic systems. Whether the timing, two weeks between the orbital closest approach and the Krakatoa peak eruption, is consistent with any such mechanism requires analysis that has not been published.
The coincidence hypothesis is the more parsimonious explanation. August 1883 was a month of concentrated global hazard by chance, and the coincidence is striking precisely because it is rare rather than because it implies a causal connection.
What the two events together reveal is a historical period in which humanity came closer to civilizational disruption than the standard historical record, focused on political and military events, typically acknowledges. The comet passed. The volcano erupted. The casualty count from the volcano was 36,417. The casualty count from the comet, if the UNAM calculations are correct, was zero because the trajectory was 538 kilometers off.
What Bonilla’s Photographs Establish
The photographs exist. They are in the Zacatecas Observatory archive. They show objects crossing the solar disk in a pattern consistent with the UNAM team’s cometary fragment interpretation and inconsistent with the birds-and-insects explanation in ways: birds and insects do not produce the elongated, irregular outlines visible in the higher-quality Bonilla images, and they do not transit the solar disk in the number and pattern that Bonilla recorded over two consecutive days.
The UNAM paper’s arXiv publication places the analysis in the public scientific record without the formal peer review validation that journal publication provides. Whether the parallax argument, the distance calculations, and the cometary disintegration hypothesis will survive formal peer review, or whether the analysis contains errors that peer review would identify, is not established by the available record.
What is established is that a recorded nineteenth-century astronomical observation has been reinterpreted by a credentialed research team using established physical methodology to produce a near-miss scenario whose calculated parameters make it one of the closest potential extinction-level impacts in the modern historical record.
José Bonilla photographed 447 objects crossing the Sun’s face on August 12-13, 1883. The editors of L’Astronomie thought they were birds.
If the UNAM team’s disputed reinterpretation is correct, they were looking at 3,275 Tunguska-scale events that were already past. If the original birds-and-insects explanation is correct, they were looking at birds.
The photographs are still in the archive. The objects are still in the images.
What passed through August 1883 left its record in a Mexican astronomer’s glass plates and disappeared into space before anyone understood what they had almost been.
