What were the 447 dark bodies José Bonilla saw crossing the Sun at Zacatecas on 12-13 August 1883?
Bonilla, director of the new Zacatecas observatory (2,502 m up), was drawing sunspots at 8 a.m. on 12 August 1883 when small bodies began crossing the Sun: 283 in two hours, 48 more in 40 minutes at noon, 116 in 45 minutes the next morning. Dark on the Sun, bright with bright trails off it, each took 1/3 to 1 second to cross. He photographed one. Mexico City and Puebla, warned by telegraph, saw nothing. The editor of L'Astronomie suggested birds, insects or dust. In 2011 three UNAM researchers proposed fragments of a broken comet passing 538 to 8,062 km away, each 46 m to 1 km across; the story spread as 'the first UFO photograph' and 'a near-extinction miss'.
Tests we ran on this
- No chance number How far away can an object be and still look sharper than the Sun in Bonilla's telescope? Under about 25 km, and within about 4 km for the blur he describes; rules out the 2011 comet distances. (decided before looking, 2026-10-26) · scoreboard
How it connects
This mystery has this clue
Optics: a 16 cm telescope cannot hold anything farther than about 23-30 km in sharper focus than the Sun; for the Sun to look blurred on Bonilla's photo, the body was within about 0.6-4 km
This mystery has this hunch or step
Bonilla's own photograph puts the bodies within a few km: birds or insects close to the observatory, not a comet
This mystery has this clue
Bonilla's report: on his photograph 'the image of the Sun is not in focus, but that of the body is'; focused on the bodies, that night the planets were out of focus and 'only the Moon was almost in focus'
This mystery has this hunch or step
Read Bonilla's 1885 report and worked out how far away his 'bodies' could be