CRUISE THE 

 MEDITERRANEAN 

 AND BLACK SEA! 





^$1134 



Explore a world of historic 

 cu ture aboard the Regent 

 Jewel - an intimate cruise ship 

 with an.attentive European- 

 trained staff. Cruise 7-days or 

 combine two itineraries for 14 

 days of incredible cruising. 



JEWELS OF THE 

 ANCIENT WORLD 



Istanbul to Dikili (Turkey), 

 Israel, Cyprus, Rhodes, Crete, 

 Santorini & Athens. 

 JEWEI5 OF THE BIACK SEA 



Athens to Kusadasi (Turkey), 

 Mykonos, Yalta, Odessa, Constanta 

 & Istanbul. 



Prices are per person, double occupancy. 

 Port charges arid fees additional Airfare 

 additional Ships registry; Bahamas- 



CRUISES INC. 



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Celestial Events 



Moonstruck 



by Gail S. Cleere 



On April 11, the moon will reach 

 apogee, its farthest distance from the earth 

 all year— 252,574 miles. On the 25th, the 

 moon will reach perigee, its closest dis- 

 tance to the earth this year — 221,790 

 miles — and because this is also the date of 

 the full moon, the full power of the moon's 

 gravitational pull will be exerted upon us. 

 Although only one ten-millionth the 

 earth's own gravitational attraction, the 

 moon's pull is enough to drag our oceans 

 over their normal boundaries. 



Perigee and the full moon coincide in- 

 frequently because the two cycles are not 

 equal. (Full moons occur every 29.53 

 days, while perigees come every 27.55 

 days.) This month, the two events occur 

 within three hours of each other, and we 

 should expect the highest and lowest tides 

 of the year on the 25th. Such events, al- 

 though they are predicted and well-publi- 

 cized, never fail to take the vast majority 

 of seaside inhabitants by surprise. 



"No more of the Universe is visible to 

 our unaided eyes than to the eyes of our 

 Neanderthal ancestors. But science, the 

 product of our imagination, has im- 

 mensely extended the range of our imagi- 

 nation," wrote astronomer Chet Raymo. 

 Most of us, however, know even less about 

 the moon than our ancestors did. We may 

 know the moon's phases but still consider 

 its monthly and annual motions a mystery. 

 The tides, the most visible result of the 

 earth's interaction with the heavens, were 

 known to our ancestors, but began to be 

 understood only after Isaac Newton pub- 

 lished his Principia Mathematica in 1687. 



Tidal swelling occurs twice a day on 

 both sides of the earth, once when the 

 moon passes overhead, and once when the 

 moon is on the opposite side of the earth. 

 Tidal forces have an appreciable affect 



only on large bodies — such as oceans — 

 and this explains why soup doesn't spill 

 over the sides of the bowl when the moon 

 is full. The sun's gravitational pull on the 

 earth is roughly half that of the moon's, but 

 when the sun, the earth, and the moon are 

 in a line (during full or new moon phase) 

 the combined force produces the higher 

 than normal "spring" tides in certain areas. 

 The effects are even more amplified when 

 the moon is at perigee, as it will be this 

 month. (Although the moon's distance 

 from apogee to perigee varies only from 9 

 to 14 percent, tidal influences can be 30 to 

 48 percent greater. The resulting high tides 

 (which usually peak one or two days after 

 perigee because of "gravitation lag") can 

 cause coastal flooding, and some scientists 

 have suggested that the chances of earth- 

 quakes and volcanic eruptions may also be 

 slightly increased. 



The actual speed and height of tides are 

 affected not only by the moon but also by 

 land masses, water depth, winds, and 

 barometric pressure. Tides typically range 

 from three to six feet, but some areas show 

 no tides at all, and others, such as the Bay 

 of Fundy, have tides of more than thirty 

 feet. If the barometer drops by one inch, 

 the seas can rise by a foot. A storm can 

 have an even larger eifect; when strong 

 winds are blowing ashore, water can pile 

 up against the coast, turning a high- 

 tide-perigee coincidence into a disaster. 



The tides do more than merely cause 

 our coastal area authorities to post notices 

 on the beaches. They also keep our 

 earth-moon system evolving. Long ago, 

 when the moon and earth were closer, the 

 earth's powerful tidal effects gradually 

 brought the moon's rotation into agree- 

 ment with its orbital period, so that we 

 never see its far side. Partly because of 



96 Natural History 4/94 



