Number 40, July 10, 1991 by Phillip F. Schewe and Ben Stein THE FIRST TOTAL ECLIPSE visible from North America since 1979 will take place on July 11. On that day far out in the Pacific the Moon's 160-mile-wide shadow will sweep across the ocean at a speed of 5000 miles per hour, passing obligingly over the poised telescopes atop Mauna Kea and thence to Mexico and South America. In the July issue of Astronomy Magazine, Alan Dyer calculates that for any one spot on the Earth's surface, total eclipses can be glimpsed only every 350 years on average; this scarcity of eclipses is due mainly to the Moon's orbit being tilted at an angle of 5 degrees to the plane of the Earth's orbit around the Sun, and because of the Moon's relatively small shadow track. Dyer reports that besides being geographically convenient to North American viewers, the July eclipse will be the longest---with a totality of almost seven minutes---until the year 2132. It is easier for the Moon to completely eclipse the Sun in early July, when the Sun is farthest from the Earth (with a solar disk of 31', 27'' in angular size) than in January when the Sun is closest (and the solar disk is 32', 31'' across.) THE MOST INTENSE EMITTER OF INFRARED RADIATION yet detected, a celestial object prosaically called 10214+4724, has been discovered by a British-American team using data from the Infrared Astronomy Satellite (IRAS). The infrared radiation, broadcast at a rate some 3 x 1014 times that of the Sun, is believed to originate from massive quantities of dust which is thought to surround either a bright quasar or a forming supergalaxy. If the presence of dust is confirmed, the object, whose redshift if 2.286, could provide evidence that heavy elements formed as early as 2.3 billion years after the Big Bang. (Nature, 27 June 1991.) ATOM INTERFEROMETRY , difficult to carry out and still only at the experimental stage, may permit new precision measurements at the atomic level. Interferometry---splitting and then recombining waves so as to make a characteristic interference pattern----has long been performed with light waves and with electrons and neutrons, but is more difficult for whole atoms, whose quantum mechanical (de Broglie) wavelengths are typically one angstrom or less. The greater the difficulty, however, the greater the potential precision. Groups at MIT, Stanford, Konstanz (Germany), and Paris-Braunschweig (Germany) hope to use their atom interferometers to make extremely sensitive measurements of rotation--with possible applications in inertial guidance systems--and acceleration. Steve Chu at Stanford believes, for example, that local gravitation will be measurable to within one part in 1010 or even 1012. (Physics Today, July 1991.) THE USE OF CLASSICAL MECHANICS in the submicroscopic realm lessened in the 1920s with the advent of quantum mechanics; atoms came to be viewed not as tiny solar systems but as nebulous systems of interacting fields. In the last two decades, however, classical methods, aided by powerful computers, have made a comeback in the study of essential quantum systems. Examples include the vibrational and rotational spectroscopy of molecules and the electronic structure of highly-excited (Rydberg) atoms. (Science, 5 July 1991.)