Zacatecas Observatory - Mexico

08:00 hrs (local), 12 August 1883

Zacatecas Observatory's boss, leading astronomer Jose Bonilla and an assistant were preparing to study the Sun's corona when he saw distant objects crossing his field of view.

During the next 36 hours the two worked continuously (through daylight hours when Sun was visible) to record the transits of those "disks" across the solar face, using the Observatory's new camera equipment.

One of Bonilla's images

said to be the `first UFO photographs'.

Early on, they counted 283 of the `craft' in two hours, but, due to the bulky photographic plates' awkward set-ups and removals, they must have seen less than the true total `flying past' during their vigil. In total they observed the passage of 447 disks.

Bonilla said some craft showed as almost perfectly circular shadows when seen silhouetted against the Sun, that they [often] traveled side by side in pairs, and [often] in groups of up to 20, and that they moved across the Sun's face in a perfectly straight line, from West to East - ie. from right to left.

Translation of Bonilla's Report

[ an `equatorial' is a telescope assembly that moves equatorially, like this early Chinese `naked-eye' observer ]

"The passsage over the solar disc of a swarm of bodies, seen at the Observatory of Zacatecas (Mexico)".

By: José Árbol y Bonilla (Director of the Observatory of Zacatecas, Mexico).

"I pursue, at Zacatecas Observatory, located two thousand 502 meters above sea level, the daily observation of the state of the solar surface; drawing, through direct and projection, sunspots and granulations, as well as the protuberances of the solar chromosphere, through the spectroscope.

To this end, I have adapted to the equatorial 0.16 m aperture, a projection device that receives on a sheet of paper a picture of Sol 0,250 m in diameter, as the field of the lens is not projected rather than on its surface 0,260 in the clear form. When the solar disc offers some interest I take photographs of 0,067 m in diameter, with plates of instantaneous gelatinobromuro silver

The dome of the observatory has small windows and thick black curtains, so that nothing penetrate the objective but the image of the Sun. This provision always allowed me to note, with precision and clarity, the details of sunspots and the granulations, thanks to the transparency of the atmosphere and the height at which the observatory is located, under a tropical sky. (22 ° 46 '34 "north latitude 9).

On August 12, 1883, at 08:00 am, I began to draw sunspots when I suddenly saw a small light entering the field of the lens, seen on the paper that I used to reproduce sunspots, and, crossing the solar-disc, it then looked like a shadow almost circular.

I had not recovered from my amazement when the same phenomenon was reproduced again, and then again, so often that in a space of two hours I could count up to 283 bodies across the solar disk.

Little by little, the clouds hampered observation, which could not be restarted until after noon, and then only for 40 minutes. During that period I counted 48 other bodies again. The paths followed by these bodies indicate a direct shift from west to east, more or less inclined to the north or south of the solar disc. During this short observation I noticed that those bodies that appeared dark-black and perfectly round and some other more or less elongated when seen against the solar disc, became bright images as they left its edges and moved across the outer field of the lens.

Their time intervals were variable, a body passing through would not take more than one third, half a second, or at most one second to cross the disc, and a minute or two passed before others appeared - some passed as 15 or 20 at once, so that was difficult to count them. I drew the trajectory of many of these bodies on the solar disc, marking their `entrances' and `exits' on the paper that I used to draw sunspots; as the lens of the equatorial moved, through a system of clockwork gears, following the apparent movement of the Sun on the celestial sphere.

The figure 118 is a small copy of the drawing I did of the solar disc that day (of 250 millimetres in diameter) with the trajectory of the bodies and sunspots.

Taking photographs of the Sun frequently, when its image shows sunspots and remarkable facula, I was already in a position to photograph this equally rare and interesting phenomenon: the passage of these bodies across the solar disc.

On this occasion I replaced in the same equatorial the objective of 0.16 m by another of equal intensity, but with a chemical focus (suitable for photographic work), which could be used optically and for the camera. After various tests to focus correctly, I managed to take some photographs, of which I have chosen I think the more interesting to send to the magazine 'L'Astronomie'.

While I took these photographs an assistant counted the bodies using the 'finder-scope' of the equatorial. The photograph was taken at Collodion process to 1 / 100 second. This speed gave me no time to properly prepare the filter and (chemical)baths but also the negative is somewhat veiled by the developer. The image of the Sun is not in focus, but that of the bodies, to which I gave at that time greatest interest.

Although in projection and to the naked eye all the bodies appeared round or spherical, it is observed in the various photographs that this is not true and that the majority have irregular shapes.

I said that, in the field of projection lens, the bodies appeared bright and left a bright trail, but across the solar disc they seemed opaque. Examining carefully the photographs and the negatives, one sees each is surrounded by a body like a dark cloudiness and a track (trail) out in the field of the lens, and, on going outside of the solar-disc, they are bright. That would make me believe that the bright trails of the bodies crossing the solar-disk absorb sunlight radiation or diminish its power, photographically.

In the afternoon the clouds prevented me from observing. Then I took certain measures and established a monitoring plan if the phenomenon were to be reproduced the next day.

On August 13, the sky was overcast until eight a.m., then the clouds cleared a bit and I was able to observe. Quickly the phenomenon was seen again, and during the 45 minutes of observation allowed us by the state of the sky, 116 bodies crossed the solar disk.

Following the observation made the previous day, I had telegraphed the observatories of Mexico [City?] and Puebla to ask them to observe the phenomena, but they were invisible to them.

In order to verify indirectly the approximate distance to the `swarm' of bodies, I had carefully prepared the `finder', the equatorial and a silver mirror lens (Eddy) 0.10 m in diameter and focussed them on the Solar-disk and then on the bodies, while at night I was able to steer this system also towards the planets and the moon, which had been in the first quarter over the past two days. Without changing the focus of the system, only the Moon was seen with sharpness.

This fact, coupled with the invisibility of the phenomenon in Mexico [City] and Puebla or elsewhere, makes me think that these bodies were close to Earth, at least at a lesser distance than the moon, and that the parallax was significant. For that reason Mexico and Puebla would not have seen them, as they would be projected outside the solar disc."

Bonilla's Original Report - in Spanish

Bonilla had noted that the objects were `luminous' and left a bright `trail' (or exhaust?) and that both object and trail were seen as `dark' or opaque when actually crossing the Sun's face.

He also saw the significance of this fact - that is, the luminosity of each object changed to a dark surrounding blur when seen against the Sun, which could be caused by a field of some sort - (even intense heat has a similar but lesser effect) whereas its bright track or trail became a dark line when silhouetted and therefore must have consisted of `matter', say a jet of gas or even of ions.

A beam of light, say, would apparear to vanish when seen against the Sun: light (photons) doesn't generally block or absorb other photons.

N.b. - the photographic `speed' of Bonilla's camera and plates was extremely slow by modern standards; so it's no surprise that such photographs would probably not show the true shapes of fast-moving objects.

As an astronomer Bonilla was well qualified to mathematically work out the direction of motion and angular `speed' of the objects, and his equipment had sufficently precise focussing for him to estimate their distance - he is reported at first as saying "not more than 300,000 kms" ie. approx 3/4s of the distance to the Moon

He later said they were about 242,000 kms away - approx. two thirds of the Moon's average distance. But there is no reported statement as to their trajectory. That is, were they departing or approaching the Earth - Moon system?