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PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 502 September 14, 2000 by Phillip F. Schewe and Ben Stein
A PLANETESIMAL AGGREGATION EXPERIMENT has been carried out in the low gravity environment of the Space Shuttle to test notions of how our solar system developed from a primordial cloud of micron sized dust particles. The experiment is the first direct re-creation, under realistic solar-nebula conditions, of the proposition that protoplanetary dust accumulates through sticky collisions amid the random Brownian motion of the particles. A consortium of German and US scientists (contact Jurgen Blum, University of Jena, Germany, 011-49-364-194-7515, blum@astro.uni-jena.de) observed that the dust quickly aggregates. The data bears out the main theory of planetesimal formation, but there was one surprise: the structures were expected to be somewhat fractal in nature, with a fractal dimension d of about 1.8, meaning that the mass of the cluster should be proportional to the cluster size raised to the d power. Instead the dimensionality turned out to be about 1.3, meaning the structures were observed to be more linear and less sheetlike (see figure at www.aip.org/physnews/graphics). (Blum et al., Physical Review Letters, 18 September 2000; Select Article.) BACK
InfoBeat <news@infobeat.com> Date: Thu, 05 Oct 2000 02:53:17 MDT
BEIJING (AP) - China's budding space program plans to explore the moon for commercially useful resources and hopes one day to take part in an international expedition to Mars, members of the secretive program said Wednesday. Speeches at a bland forum by the head of the State Aerospace Bureau and a key researcher gave rare glimpses into the military-dominated program. Although details were few, the experts made one thing clear: China sees manned space flight as key to securing its international stature and economic survival. China's manned space program, given the secret designation Project 921, has gathered momentum in recent years, getting help from a more experienced Russia and bigger budgets from a government eager not to fall further behind the West. See http://www.infobeat.com/stories/cgi/story.cgi?id=2570361152-d31 . BACK
Stars said to tell age of pyramids
(AP) - Just how old are the pyramids? The answer may lie in the stars. Current estimates for the construction of the pyramids, based on surviving lists of the pharaohs, are believed to be accurate to within about 100 years. But Cambridge University Egyptologist Kate Spence says that by analyzing the relative position of the Earth and two stars, she has dated the construction of the Great Pyramid at Giza - one of the Seven Wonders of the Ancient World - to within five years of 2478 B.C. That means the Great Pyramid is 4,478 years old - or 75 years older than one commonly accepted estimate. Her estimate comes from her proposed solution to another mystery: How did the ancient Egyptians align their pyramids so that two sides ran so precisely north-south? She suggests that they used a pair of stars found in the Little and Big Dippers. But because Earth wobbles on its axis, those two stars would have given different indications for "north" over the centuries. So by calculating when that pair of stars would have been in a northern alignment, Spence says she can figure out when the pyramids were built. In the 16 Nov 2000 issue of the journal Nature, Spence says the two-star method could explain the various degrees of inaccuracy in the orientation of pyramids built at different times.
PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 513 November 22, 2000 by Phillip F. Schewe and Ben Stein
COSMIC RAYS AND CLOUD COVER. Galactic cosmic rays (GCRs) play an important role in controlling global cloud cover on Earth, according to recent studies by researchers at the Danish Space Research Institute in Copenhagen. GCRs, consisting principally of energetic protons emitted from stars within our galaxy, are a primary source of the atmospheric ionization which affects cloud formation. Because cloud cover has an impact on both the reflection of solar radiation and the retention of heat in the atmosphere, correlation between GCRs and low level clouds suggests a link between global climate changes and cosmic ray flux. The discovery reveals a convoluted connection between solar variability and climate change. Fluctuations in the sun's radiative output are generally dismissed as too small to account directly for global warming and other climate variations. Periods of intense solar activity, however, lead to powerful solar winds which shield the atmosphere from cloud-forming GCRs, potentially modulating the global climate. (N. D. Marsh; H. Svensmark, Physical Review Letters, 4 December.) Researchers at the University of Leeds (UK), on the other hand, have observed a direct and rapid connection between atmospheric chemistry and ultraviolet light from the sun. During the 97% eclipse of the sun over Ascot, England, local ozone concentrations fell to 60% of typical daytime levels, and quickly returned to normal after the event. The study demonstrates the dynamic connection between sunlight and the photochemistry of atmospheric gasses which may contribute to global warming, smog formation, and acid rain. (J. P. Abram; et al, Geophysical Research Letters, 1 November.)