Sky & Telescope July 1987 [antikvár]

50 and 25 Years AgoThe SkyJuly, 1937Investigations of meteors occurring in showers have shown that the skeleton framework of a comet consists of meteoric material. As the comet slowly disintegrates and loses its conspicuous outer cloak of gas and dust, the meteoric skeleton is slowly distributed about the orbital path. If the Earth's orbit crosses this path a meteor shower occurs at each crossing. Several such showers have been identified with known comets that have disappeared, but a great many meteors are not associated with the showers. The origin of these "casual" or "sporadic" meteors has been studied by Dr. Ernst Opik in a Harvard Observatory expedition to Arizona. He finds that a large percentage of the faint telescopic meteors originate outside of the solar system.. . . Opik has observed the speeds of meteors visually by means of an oscillating mirror in front of an inverted telescope. Photographically, the speed can be determined by means of a rotating shutter in front of the camera lens. The shutter breaks the meteor trail into segments that can be measured accurately. . . . If a second camera at another station photographs the meteor simultaneously, the distance, height, direction of motion and speed of the meteor can be determined. . . .In the fifteen months that the observing programs of these two telescopes [located at Harvard Observatory and its Oak Ridge station] have been synchronized, six meteors have been photographed simultaneously. Dr. Fred L. Whipple has, to date, measured and reduced five pairs of these meteor photographs. . . . Four of the five had been moving in elongated elliptical orbits about the Sun and were therefore members of the solar system. One had been moving in an hyperbolic orbit, indicating an origin in interstellar space outside the solar system.Scientists argued about the existence of substantial numbers of "hyperbolic" meteors and their possible significance for many years. The early observations of such bodies were probably in error and currently there are no confirmed examples.Sky & Telescope July, 1962Scientific cooperation between nations toolt a major step with the launching on April 26th of a British satellite by an American rocket. Completely designed and built by United Kingdom scientists, the instruments aboard are gathering data on the ionosphere and the sun's effect upon it. . . .The world's first international satellite was christened Ariel lettersNot So FastC. J. Chrones may have misinterpreted his observation of Jupiter (April issue, page 457). Havitig made several similar sightings, I believe that the distortions he saw of Jupiter's image were due to turbulent condensation trails (contrails), rather than shock waves froni a jet aircraft.Contrails sometimes two, three, or four in number depending on the aircraft's complement of engines often appear to drift across the sky at surprising speeds when blown by high-altitude winds. Viewed telescopically, they seem to move even faster.A true shock wave would travel so fast it would be nearly impossible to view under the conditions described by Chrones. Furthermore, such shock waves would create the classic sonic booms, which haven't regularly been heard over the United States since the 1960's.GREGORY A. BURNETT 37567 Radde Mount Clemens, Mich. 48043CHON-ChowIn your fine issue on the anatomy of Comet Halley (March, 1987), I found one inaccuracy. The acronym "CHON" (for dust formed of carbon, hydrogen, oxygen, and nitrogen) was not invented by the Halley flyby investigators. The term originated in science fiction.In Beyond the Blue Event Horizon by Frederik Pohl (Del Rey, 1980), earthlings explore a processing plant built in the Oort Cloud by a race of ahens. Its function is described this way:The idea of mining comets for food wasn't new, it went back to Krafft Ehricke in the 1950's It made sense. Bring along a little iron and trace elements the iron to build a place to live in, the trace elements to turn CHON-chow into quiche lorraine or hamburgers - and you can live indefinitely on the food around you. Because that's what comets are made of. A little bit of dust, a few rocks, and a hell of a lot of frozen gases Oxygen Nitrogen. Hydrogen. Carbon dioxide. Water! Methane. Ammonia. The same four elements over and over again. CHON What comets are made of is the same thing you are made of, and what C-H-O-N spells is "food."An idea to keep in mind when we set out to colonize the solar system.TONY HOFFMAN 9 Bank St.New York, N. Y. 10014Circles and EllipsesAllah Chapman's fascinating article on angular measurement in the 1600's (April issue, page 362) contains several statements that reinforce a widespread misconception about the difference between circular and elliptical orbits. He writes, "When astrondmers considered Kepler's ideas, they realized that if the Earth moved in an ellipse the Sun's apparent diameter should change slightly over the course of a year."This is true, but it is also true for the off-centered circular orbits used by both Ptolemy (geocentric) and Copernicus (heliocentric). The difference in apparent solar diameter with the Sun on a properly placed eccentric circle and on an eUipse is less than 0.02 percent, or 0.3 arc second. It could not have been detected by the 17th-century methods Chapman recreated.In fact, neither Ptolemy nor Copernicus had a properly placed eccentric circle for the Earth-Sun arrangement, and it was one of Kepler's early triumphs to realize that both of his predecessors had mistakenly doubled the eccentricity. Hence it was easily possible for Jeremiah Horrocks or William Gascoigne to detect that the Kep-lerian eccentricity was the correct one, even though they could not possibly have measured the difference between a