In August of 1883, Mexican astronomer José Bonilla pointed his telescope at the sky and recorded an astonishing event: some 450 mysterious objects passing in front of the Sun, each with misty trails.

Three years later, he finally publishes his account of the events in the French journal L'Astronomie -- but the incredulous editor shrugged the bizarre sighting off as insects or dust dancing across Bonilla's telescope. Now, 125 years later, a modern astronomer wants to set the record straight.

Hector Manterola at the National Autonomous University of Mexico in Mexico City, and colleagues, interpreted Bonilla's observations and used his results to estimate the distance at which the objects glided over the Earth's surface, their size and their mass. Manterola's hypothesis? A massive comet that had recently broken up and fragmented.

The team believes that the fragments would have careened past Earth as close as 600 to 8000km from the planet's surface, and the individual chunks would have been anywhere from 50 to 800km wide. What's more, the intact comet, before it spilled its guts over the sky, could have weighed a billion tonnes.

If the comet had hit Earth back then, we definitely wouldn't be around to write this article. But each indidual fragment would have been roughly as big as the object that was thought to have hit Tunguska in 1908 -- an event 1,000 times more powerful than an atomic bomb.

After working out an estimated number of objects that would have whizzed past between Bonilla's observations, Manterola concludes, "if they had collided with Earth we would have had 3275 Tunguska events in two days -- probably an extinction event." Probably.

So why was this one astronomer at a small observatory in Zacatecas the only person to spot this narrowly-avoided extinction comet? Manterola and friends have an answer for that, too.

Because the fragments were so close to Earth, parallax says that only those in line with the Sun and the comet chunks would have been able to easily see the pieces. Mexico is at the same latitude as the Sahara, northern India and south-east Asia -- which weren't exactly astronomy hotspots in 1883.

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