Abstract of talk by Duncan Steel
Spaceguard Australia, P.O. Box 3303, Rundle Mall, Adelaide SA 5000, Australia. Email: dis[at]a011.aone.net.au
Presented at the SIS Conference: Natural Catastrophes during Bronze Age Civilisations (11th-13th July 1997)
Astronomical hypotheses for the purpose(s) of megalithic monuments have mostly been implicitly based upon an assumption that the designers witnessed the same phenomena as those we observe in the sky today. This assumption is not well-based for phenomena having time-constants of order centuries or millennia, such as the populations of comets and meteoroids in the inner solar system and the ephemeral meteor showers and storms which they produce on the Earth. IRAS observations have indicated that Comet Encke has a trail (not tail) of debris some tens of millions of kilometres long, presumably produced since its latest period of activity began about 200 years ago. One may further presume that the Taurid meteor showers we observe in this epoch are the result of the dispersal of trails produced in previous activity cycles which must stretch back to about 20,000 yr ago. When the comet, accompanied by such a trail, has a node close to 1 AU, one expects intense meteor storms to occur, perhaps accompanied by multiple Tunguska-type events if the disintegrating comet spawns massive lumps of debris. Determination of the epochs of such events from backwards integrations is impossible due to (i) Chaotic orbital evolution; and (ii) Non-gravitational forces, but pairs of intersections (one at the ascending node, the other descending) are to be expected a few centuries apart and separated by 2500-3000 years. It is suggested here that one such pair occurred in 3600-3500 and 3200-3100 BC, provoking the construction of the Great Cursus and Stonehenge I. From Stonehenge I, apparently the first construction at the famous site, as the comet neared the Earth it would have appeared to rise in the evening with a huge bright stripe crossing much of the sky, originating in the north-east. Passage through the trail would then result in celestial fireworks (and maybe worse); afterwards the comet and trail would have passed in the direction of the Sun, partially blocking sunlight for a few days. In order for terrestrial intersection to have occurred in that epoch (late fourth millennium BC) the mean orbital period of the comet over the past 5,000 years would need to have been slightly less than at present, and might then be expected to have produced a 19 year periodicity in meteor storm events (six cometary periods). It is suggested that Stonehenge I was built by the Windmill Hill people to allow the prediction of such events, from which they hid in the shelters we now call long- and round-barrows, and that the later developments at Stonehenge (phases II and II) by the Beaker people were a result of a misinterpretation of the original purpose of the site in terms of lunar and solar observations, a misinterpretation which was re-discovered by Newham, Hawkins and Hoyle in the 1960's.
DUNCAN STEEL is director of Spaceguard Australia and Vice-President of The Spaceguard Foundation. Steel took B.Sc. and M.Sc. degrees at the University of London, studying at various colleges, and then moved to the University of Colorado where he worked on NASA's Pioneer Venus Orbiter program. He then moved to New Zealand, where he took his Ph.D. degree at the University of Canterbury for work on radar observations of meteors. He continued this work from 1985-96 at the University of Adelaide, Australia, spending 1987 as an ESA Fellow at the University of Lund, Sweden. From 1990 until its termination in 1996 he directed the only southern hemisphere program for the discovery and tracking of near-Earth asteroids, based at the Anglo-Australian Observatory. In connection with this he has served on various international committees, including NASA's Spaceguard committee in 1991-92 and the International Astronomical Union's Working Group on Near-Earth Objects since 1991, and Working Group on the Prevention of Interplanetary Pollution since 1988. He is the author of over a hundred scientific papers, and the book Rogue Asteroids and Doomsday Comets" (Wiley, Chichester and New York, 1995). In addition, he has appeared in numerous TV and radio documentary programs concerned with the impact hazard.
Presented at the SIS Conference: Natural Catastrophes during Bronze Age Civilisations.