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Mercury, September/October 2004 Table of Contents

Courtesy of NASA/JPL

by Graeme H. Smith

The Moon is the only alien world whose surface can be explored in detail by Earth-bound observers. Through even a modest telescope the lunar terrain offers a rewarding spectacle.

Many professional astronomers feel no affinity for Earth's celestial companion, however. A gibbous Moon floods the night sky with reflected sunlight, swamping the highly-prized photons arriving from distant stars and galaxies. Moreover, moonlight halves the amount of time each month during which these objects can be studied. And telescopic views of the Moon cannot match the details of photographs returned by the Apollo program, as well as electronic images obtained by unmanned lunar orbiters and landers. Consequently, after the start of space programs in the United States and the former Soviet Union, scientific study of the Moon moved from the province of the astronomer to that of the geologist and planetary scientist.

So how did professional astronomers feel about the Moon at the beginning of the 1900s, when the study of the lunar surface was still the domain of optical Earth-bound telescopes? In 1904, the great observer Edward E. Barnard wrote: "It is a fact that the Moon has been badly neglected visually, in recent years, and that its study has been relegated to the amateur with small instrumental means. The large telescopes of today have never seriously taken up its study. Yet there is perhaps no object in the sky that would more probably repay the careful observer than a close study of the Moon's surface." This surface, Barnard concluded, would "offer a rich field for careful and original investigation with sufficiently powerful telescopic means."

It may be that some astronomers felt the same way as William W. Campbell, who wrote of his interest in lunar craters in 1920 when he was director of Lick Observatory. This interest had been sparked while he was "engaged in showing the Moon through the 36-inch refractor to many thousands of Saturday evening visitors." Campbell's main research at that time typically dealt with stars and planetary nebulae, but he appears to have had at least a part-time interest in the Moon, and engaged in the debate over the origin of lunar craters.

Even so, Barnard's comments seem somewhat curious, given that in the 1890s several notable observatories had embarked on the production of the first large-scale photographic atlases of the Moon. Although only a small number of professional astronomers devoted substantial amounts of telescope time to lunar observations, one of those who did was well known to Barnard. Edward S. Holden, the first director of Lick Observatory, started a photographic campaign in 1890, while Barnard was still a Lick astronomer before moving to Yerkes in 1895. At that time the flagship of Lick Observatory was the great 36-inch refractor on Mount Hamilton. This telescope would be used for two extensive programs of lunar photography that have left a considerable pictorial legacy, one of which harkens back to a time when the past history of the Moon was as mysterious as is the evolution of distant galaxies to astronomers today.

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