What Makes the Shadows Hot

The more they improve their techniques, the more they refine their measurements, the more problems astronomers seem to discover. But the very recognition of those problems may point the way toward prediction of the weather of the universe, toward the type of forecast that will be essential for far-voyaging astronauts.

Cool Sun. When they set up their cameras in a Douglas DC-8 jetliner and flew high over Canada during last summer's eclipse, Drs. Guglielmo Righini of Italy and Armin J. Deutsch of the U.S. counted on snapping some of the clearest pictures yet of the sun's glowing corona. But up there above the dust, water vapor and other difficulties of the earth's atmosphere, the two astronomers told the Florence meeting of COSPAR (Committee on Space Research), they found far more than they expected. Their pictures of the sun's spectrum showed a strange line that had not been predicted by any of their calculations.

Not that the line was hard to identify; its wave length showed that it came from ionized calcium atoms that have lost one electron. But where did this calcium come from? At the corona's temperature, 3,000,000-o, calcium loses nearly all its 20 electrons and shows the loss by emitting a different kind of light. In the singly ionized state, calcium cannot exist above a comparatively frigid 20,000-o.

Drs. Righini and Deutsch now believe that there must be cool spots in the corona, but they can only guess at the mechanism that makes these cool spots possible. Perhaps, they say, the corona is threaded with magnetic fields that churn it around, making it lumpy and unevenly heated. Whatever the final explanation, it may provide an insight into solar flares, the violent sun storms which generate radiation that can kill a man in space.

Hot Shadows. Jupiter's temperature now seems as mysterious as the sun's. Astronomers Bruce C. Murray and Robert L. Wildey of Caltech uncovered that surprise by placing a new infrared photometer at the focus of Palomar's 200-in. telescope and taking the temperature of Jupiter's cold atmosphere. Although the photometer designed by Engineer James A. Westphal is 20 to 50 times as sensitive as earlier instruments, it registered no change as it scanned the Great Red Spot and the light and dark bands that decorate Jupiter's disk.

Then the scientists spotted another quarry: the shadow of Jupiter's satellite Ganymede, which is bigger than the earth's moon. They expected the shadow to be colder than the surrounding area, just as the moon's shadow casts coolness on the earth. To their surprise, the temperature reading rose more than 100-o, from -230-o F. to -117-o F., as the photometer focused on the shadow. Incredulously, they repeated the experiment many times, always with the same result. The shadow of another satellite, Europa, proved to be equally warm.

The two scientists offer two explanations, both of them uncertain. Perhaps the passage of a satellite's shadow may disturb Jupiter's atmosphere in some way, permitting warmer lower layers to rise upward and be detected from the earth. Or perhaps the interruption of sunlight stops a photochemical reaction in Jupiter's high atmosphere, making it temporarily more transparent so that radiant warmth from below can escape into space.

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