WHAT IF THE MOON DIDN'T EXIST?

Ten ``what-if'' astronomical questions-and-answers comprise this clever effort by Comins (Astronomy and Physics/Univ. of Maine), who writes often for Astronomy magazine. One solution to the title query and all the rest is, to put it baldly: ``bad news for us.'' Without a moon, the earth would rotate three times faster, high winds would roar down hill and dale, and human evolution would be severely cramped (although telepathy might become our favorite sense). Comins delves into biology, astronomy, geology, and a host of other sciences to paint his scary scenarios. Would we have better luck if the moon were closer than it is? Don't get your hopes up: We'd face giant tides, icebergs galore—and, Comins speculates, humans that would be less sociable than the current crowd. What if the earth had only two-thirds of its present mass? There'd be no earthquakes, the globe being far more solid than it is now—but we'd be hammered by meteors. Well, what if the earth's axis were tilted, like that of Uranus? Every place except the equator would suffer from week- or month-long nights and days, and the polar caps would melt each year, terrible news for coastal real estate. What about a more massive sun? Runaway greenhouse effect or runaway glaciation. And so on for other disasters: a supernova near the earth; a rogue star visiting our neighborhood; a black hole boring through the planet. Comins concludes with two variations on the theme: What if we could see in spectrums other than visible light (infrared, ultraviolet, etc.), and what if the ozone layer were depleted? The latter is a plea for action, as the author notes that this scenario is unfolding even now. Lots of fascinating lore—but by the fifth or sixth catastrophe, readers may be reaching for a bromide.