Archive for September 23rd, 2010

Halley’s comet was observed by ancient Greeks?

I would like to share with the reader a short analysis of an article in the Journal of Cosmology about the possible connection of the so-called Comet of the 78th Olympiad observed by the ancient Greeks in 466 B.C. and the comet which today is known as Halley’s comet. The article was interesting to me, but quite frankly, the original didn’t have much credibility. There was not a word about how scientists calculated the position of the comet 2500 years ago, nor any technical description.
I tried to get similar results with the help of the JPL HORIZONS system. Taking the osculating elements of the comet for 239 B.C. (SAO/-239), I used back integration of the position of the comet 227 years ago (JPL DE406).
Actually, it seems that Comet Halley passed by the Earth in 466 B.C. Its minimum distance from the Earth was at the end of June – beginning of July, passing at a distance of 0.48 A.U. (71.8 million km). The comet was visible to the unaided eye from June to August. At the beginning and end of the first two summer months, the Moon didn’t interfere with finding the comet in the dark skies of Chalcis. My estimate of the brightness of the comet is a little higher than that of Graham and Hintz (Graham et al., Journal of Cosmology 2010, Vol. 9). Its maximum brightness would have been mag. 2, but that, of course, is a complex issue and here the fact that we are working with 2500 year-old data plays a major role, in other words, some 33 orbits of the comet around the Sun in which each time the comet approached the Sun, it lost more and more material.
At the beginning of June, Halley was visible low in the pre-dawn sky. By the end of June, the comet had moved to the evening sky and it was visible low above the horizon, not more than 10 degrees. Since it had decreased in brightness, it had already became a difficult object to observe. From this information, I support the hypothesis that the ancient Greeks observed only the “young” (of course by man’s reckoning) Comet Halley. There would still be 2244 years until its “discovery”…

September 2010
« Aug   Oct »