Number 20: 24/05/2003
A scientific publication by SGF and NEODyS

The history of NEOs' science
The discovery of EROS: a peculiar 3body problem
by Ettore Perozzi - Telespazio

The discovery of the first NEA (433) Eros from the Urania Sternwarte Berlin on the night of the 13 August 1898 was announced by Gustav Witt both on the Astronomiche Nachrichten and the Astronomical Journal. But this simple statement does not tell the whole story: according to a recent study by Hans Scholl, Francoise Leguet-Tully, Marie Christine Gay (Observatory of Nice) and Lutz D. Schmael (Heidelberg) the events behind the discovery of Eros are definitely more complex and involve more than one single astronomer. Let us then go back in time until October 5, 1898: Octave Callandreau (professor of astronomy at the prestigious Ecole Polytechnique) reports to the general assembly of the Société Astronomique Francaise. While addressing the discovery circumstances of the new peculiar asteroid, he states: "It is certain that the planet 1898 DQ [i.e. Eros provisional designation] was observed in Nice on august 13, the same day as in Berlin. In order to complete his observation of August 13, Monsieur Witt made observations on August 14 and 15, which were respectively a Sunday and a holiday. I suppose that Monsieur Charlois had to postpone his observations until Tuesday, August 16, and that was sufficient for him to lose the merit of an important discovery". Alfred Cornu - session president - also reminds the assembly that one year before the discovery of Uranus by W. Herschel, the French astronomer Pierre Lemonnier (1715-1799) saw the planet twice in a month, but failed to recognize it because he did not reduce his observations.

But who was then Auguste Charlois? At the end of the century he was the leading discoverer of asteroids with a detection rate of about 60%, a pioneer in using the new technique of taking photographic plates of celestial bodies, a very reliable and regular observer of minor planets. With respect to him, Witt's interest in asteroids was essentially focused in recovering objects with poor ephemerides. This difference reflects also in the reason why both astronomers were observing the same region of the sky on that historical night. Charlois was carrying out a routine observation of asteroid (119) Althaea at opposition, while Witt hoped to recover the long-lost minor planet (185) Eunike. Was then really Charlois' negligence which prevented him from discovering Eros? Does he deserve such a long-lasting blame? (NB: in the year 2000, an article on the French newspaper Le Monde still gave full credit to Callandreau....). A reliable answer is provided by the afore mentioned research: after carefully examining Charlois observation logbook and a number of other facts and figures, the conclusion is that Charlois was in the worst conditions an astronomer can possibly imagine for discovering a celestial body. And not by his fault. First of all he had a mechanical problem with the telescope (as duly reported in his logbook) which was not following the diurnal motion of the stars, which then appeared as trails. But even so he could still be able to recognize the trail left by Eros, which could have a different length and direction. Unfortunately on this particular night the apparent motion of the asteroid was almost exactly parallel to the diurnal motion of the stars! Additional technical problems with the telephone/telegraphic system used for fast communication with the astronomical community cannot be excluded. On the other hand it is well assessed from meteorological data records that the weather conditions during the weekend were stormy in Nice while in Berlin - surprisingly enough - the sun was shining and the nights were clear. Last but not least, the of August is holiday in France (as for most southern Europe countries) but not in Germany ("Our summer is winter painted in green" used to say the German poet Heinrich Heine...).
The non trivial amount of bad luck suffered by Charlois still lasts: when the researches tried to resume the original photographic plate of Eros taken by Charlois as a final proof for his redemption, they were unable to find it. Apparently the whole collection of his plates disappeared from the archives of the Observatoire de Nice (only retired colleagues could remember having seen them around until the late sixties).

But just at the end of the story, another character enters the scene: Felix Linke (1879-1959), who assisted Witt since 1897 in guiding the telescope-camera combination during the long exposures as a result of the poor telescope mechanics. From the observed trail of Eros in the only surviving picture of its discovery one can deduce that the exposure duration was of approximately 103 minutes, which highlights the fundamental contribution of Linke to the success of that specific observation!
When looking for Eros in the Dictionary of Minor Planet Names, one reads: "Discovered by G. Witt at Berlin and independently discovered by A. Charlois at Nice". In the light of the historical facts presented so far, one is tempted to ask for a "revised" statement giving the full status of co-discoverers to the three of them: Charlois, Witt and Linke.