National Geographic : 1958 Feb
you would see the sun eclipsed by earth, a dra matic spectacle. Our planet's darkened circle would be rimmed with a coppery glow, where sun light trickled through the earth's gaseous shell, emphasizing the red shades of sunset. Dressed as a space traveler, burdened with oxygen tanks, space helmet, and other protective devices, you might weigh on earth as much as 300 pounds. On the moon, because of its smaller size and reduced gravity, you would weigh only one-sixth as much, or 50 pounds. An athlete who on earth high jumps over a six foot bar elevates his body's center of gravity an average of about three feet. On the moon he could leap 21 feet with similar effort (page 295). And, from this height, he would fall with a shock or im pact no greater than that associated with the six foot jump on earth. To feel normal on the moon, the space traveler would have to wear leaden shoes weighing at least 300 pounds each. Powder Masks the Moon's Wrinkled Face A thin layer of dust covers the lunar surface from a depth of several inches to perhaps several feet. One prominent scientist has argued convincingly that the dust cover may be miles in thickness and that the craters themselves are dimples in this layer. As you kick the dust upward, no billowing cloud remains behind, because even the finest particle, free of any atmospheric buoyancy, falls back as rapidly as it rises. The dust surface is marred by indentations rang ing in size from tiny impressions no larger than a dime to pits many feet across. These grade in turn Moon's Position Relative to Sun and Earth Determines Its Phases To primitive man, the waxing and waning of the moon was one of nature's most puzzling mysteries. Astronomy, oldest of sciences, long ago explained the phenomenon. Like the earth itself, half the moon is always in sun light, half in shadow. As the moon journeys around earth, the lighted portion visible to us varies according to the moon's position. Astronomers recognize eight such variations, or phases. They occur within a period of 29/ days, the interval from new moon to new moon. In the diagram (center) you are looking directly down on earth and moon. You see the moon in nine positions. Now note the ratio of light and shadow that the lunar face presents to earth in each phase. What astronomers call the new moon (top) is invisible to earth because it turns its back directly to the sun. About three days later the poets' new moon (slightly left) shows an ultrathin crescent of light. On the opposite side of its orbit, the moon presents its sunlit face to earth and is full. Photographs of the phases correspond to positions shown on diagram. "Gibbous" (from the Latin gibbus, hump) refers to the moon's swollen aspect between the quarter and full phases. Sinus Medii (Middle Bay) is a central point on the face of the moon (see map, page 287).