Monday 17 October 2011

OT - 1883 Zacatecas observation of objects before sun were not 12P/Pons-Brooks fragments [updated]

A rather weird story has been posted here on the Technology Review website, based on this paper posted on

In it, Manterola et al. discuss an observation from 1883 by Jose A. y Bonilla from the Astronomical Observatory of Zacatecas, Mexico. On August 12th and 13th, he observed objects passing in front of the sun during telescopic solar observations. These objects were "misty" (= unsharp?) and crossed the sun in about 1 to 1/3 seconds of time. They were not seen during simultanious observations from other Mexican observatories. The observations were published in L'Astronomy in 1886, and the editors put it down to dust in the telescope system, birds or insects crossing the FOV.

Manterola et al. now make an argument that it were cometary fragments passing as close as 800 to 6000 kilometers (!) from earth, suggesting Earth narrowly escaped a shower of cometary fragment impacts. They also argue that it were fragments of comet 12P/Pons-Brooks.

The latter theory can be quickly falsified (and so can be the suggestion that it were comet fragments passing close by earth). The 1883 nodes of the orbit of comet 12P/Pons-Brooks were at solar longitude 255.8 deg (ascending node) and 75.9 deg (descending node), corresponding to December 6 and June 5. The latter (descending node) is far away from earth, beyond Saturn's orbit. The ascending node is closer, but still closer to the orbit of Venus than to the orbit of Earth.

This means that the earth only comes (not particularly) close to the cometary orbit near this date, and hence any fragments in similar orbits can only come close to earth on this date: December 6. Not on August 12-13, the date of  Bonilla's observations.

The diagrams below show how the earth is nowhere near 12P/Pons-Brooks' orbit on August 12-13, passing closest on December 5-7 instead (with the comet orbit at 0.2 AU minimum distance from Earth orbit: closer to Venus than to Earth):

click diagrams to enlarge

It should also be noted that the MOID between the Earth orbit and the comet's orbit is not particularly close (minimum 0.2 AU). Hence, it does not tally. These cannot realistically have been 12P/Pons-Brooks fragments.

The whole story seems far-fetched and very unlikely.

The "fuzzy" character of what Bonilla describes to me suggest out-of-focus objects, i.e. close by (with the telecope focussed on the sun), well within the Earth atmosphere and most likely within the telescope system. The "dark before sun disc, bright outside disc" is very odd, especially the latter - objects need to be very bright to outshine the sun and (presumably) a solar filter so close by the sun.

Moreover, the non-observation by other observatories (e.g. Mexico City) conducting solar observation that same day, is deadly to the hypothesis. Manterola et al. try to explain this by parallax, arguing that this must mean the fragments crossed very close to earth. However, the total observation time of the objects was 3h25m. Earth moves about 6150 km 370 000 km (about one Earth radius one earth-lunar distance) in it's orbit during that time, and the earth's surface rotates a considerable distance in this timespan too. This is deadly for the "restricted visibility area through parallax" argument. The area of visibility should be thousands of km wide, otherwise Zacatecas could not have had visibility for over 3 hours. The objects therefore really should have been seen from other places as well.

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