Twinkle, Twinkle

Men who see red giants and white dwarfs in the night met 200 strong last week at the Yerkes Observatory, Williams Bay, Wis. Members of the American Astronomical Society, they reported to one another:

> The moon's great craters are extinct volcanoes and not meteoric pockmarks as many scientists have believed. So said Roy K. Marshall of Philadelphia's Franklin Institute. His reasoning: If the moon has no atmosphere at all, a one-inch meteorite traveling 20 miles a second would strike it with an explosion visible from the earth. About 1,000 meteors that size must have fallen moonward in the past century, but no explosion has been seen. Therefore, the moon must have enough atmosphere to consume them long before they could make pockmarks. Probably it is only one millionth as dense as the earth's atmosphere at the surface, but 80 miles up it may be as dense as ours (because of the moon's lesser gravitational pull), and the earth's atmosphere 80 miles up is still dense enough to destroy most meteors in a flash long before they get near the lower air.

> Unique among the 9,000 carefully studied stars is 17 Leporis in the Constellation of the Hare: every five months it casts off a shell of hell-hot vapors, much as a snake casts off its skin. So said Otto Struve and Burke Smith of the University of Chicago.

> The debris of the fantastically brilliant exploding star recorded by Chinese stargazers in 1054 A.D. now forms the Crab nebula. "This star shone temporarily ten times brighter than the moon," said Rudolph Minkowski of Mount Wilson Observatory, "and was visible for a full month in the daytime sky. It was . . . one of the three supernovae which have appeared in the Milky Way during the last thousand years. The others were Tycho's star in 1572, and Kepler's Nova of 1604." In Pasadena next day Minkowski's colleague, Walter Baade, announced finding the debris of Kepler's supernova, which for a while shone as bright at its source as 25,000 suns.

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