On the evening of July 29, 1953, Mr. J. J. O’Neill, a science reporter for the New York _Herald Tribune_, was looking at the moon through his small telescope when he saw what he believed to be a shaft of light shining from the mountainous ridge above the Mare Crisium crater and fanning out into the shadowed area of the crater wall. According to his interpretation, the light was coming from underneath a new structure, a gigantic natural bridge twelve to twenty miles long that arched over a gap in the mountainous rim. This region of the moon had been thoroughly studied and mapped during the previous century and no such feature had ever been noticed. The sudden appearance of so spectacular an object, if true, would indeed require explanation. Alerted by news reports of the moon bridge, a British amateur astronomer, H. P. Wilkins, reported a few weeks later that he, too, could see the mysterious arch through his telescope (see Figure 16). To saucer enthusiasts these reports constituted proof that the moon was inhabited. Since Nature alone could not have formed such an arch in so short a time, they argued, the bridge must be artificial. The structure might have been built by creatures living on the moon, perhaps in enormous underground cities. These beings might be native Selenites, or they might be colonists from Mars or from planets belonging to another solar system who were using the moon as a base for their spaceships[XI-16]. [Illustration: _Figure 16._ The “Moon Bridge.” A, Just before sunset light fans out from beneath “arch”; B, the fan narrows as sun sinks lower; C, fan begins to disappear as sun sets below horizon. (Based on sketches by the late H. P. Wilkins.)] Professional astronomers, queried about the mysterious bridge, pointed out that sunlight could not have produced the phenomenon in the way described. When a bright lamp shines through an open doorway into a darkened room, the light spreads out like a fan into the shadowed area because the light source is very near. But the supposed light source in this case was the far-distant sun. If a shaft of sunlight were shining under a huge lunar arch, as claimed, the opposite boundaries of the illuminated area would be essentially parallel, not divergent like the fan-shaped region described. Examining the Mare Crisium wall through the fifteen-inch Harvard telescope, Dr. Menzel (who was therefore labeled “one of the Army stooges”[XI-16a]) concluded that the bright area observed by the amateurs must have been a high plateau that was still illuminated by the setting sun while the rest of the crater wall was already in darkness. The roughly curved boundary of the illuminated plateau, seen against the shadowed mountains, had been mistakenly interpreted as a bridge. Dr. G. P. Kuiper, one of the world’s leading authorities on the moon, also studied the area with the eighty-two-inch reflecting telescope at the McDonald Observatory, and reached the same conclusion.