Get to Know 

 The St. Joe Company 



and Receive Two Free 

 Admission Passes 



Register at JOE.com I Keyword: museum 



and get TWO FREE ADMISSION PASSES 

 to special exhibits at 

 these participating museums 

 and science centers: 



Museum of Arts & Sciences 



Daytona Beach, Florida 

 featuring "Glories of Ancient Egypt" 

 through May 7 



Florida Museum of 

 Natural History 



Gainesville, Florida 

 featuring "Glow: Living Lights" 

 through May 29 



Orlando Science Center 



Orlando, Florida 

 featuring "Moneyville" 

 through April 30 



Mary Brogan Museum of 

 Art and Science 



Tallahasee, Florida 

 featuring "DINOSAURS: 

 Mesozoic Urban Legends" 

 through May 1 4 



Museum of Science & Industry 

 (MOSI) 



Tampa, Florida 

 featuring "Animal Grossology" 

 through April 30 



^STJOE 



IF YOU DON'T KNOW JOE, 

 YOU DON'T KNOW FLORIDA. 



Offer includes free passes only and expires 

 May 1 5, 2006. Quantities limited. 



light that reaches it. By comparison, 

 primarily because of all the white 

 clouds in Earth's atmosphere, but also 

 because our vast oceans reflect a good 

 deal of light, a patch of our planet's sur- 

 face material is, on average, three times 

 more reflective than an average patch 

 of the Moon. And because Earth is 

 more than three and a half times wider 

 than the Moon, it has thirteen times 

 more surface area to do the reflecting. 

 So, full Earth as seen from the Moon 

 is forty times brighter than the full 

 Moon as seen from Earth. You could 

 easily read by earthlight. Full Earth re- 

 flects a lot of light back out into space. 

 And when that light reaches the Moon, 

 enough is reflected from the otherwise 

 unlit portion of the near side to make 

 the dark surface faintly visible to the 

 naked eye on Earth. 



So yes, earthshine is real. So is moon- 

 shine, as we all knew already. But earth- 

 rise is not. From the near side of the 

 Moon, tidally locked and forever fac- 

 ing Earth, our planet simply hovers in 

 the sky, where it neither rises nor sets. 

 The famous "Earthrise" photograph, 

 taken in 1968 by Apollo 8 astronauts, 

 was snapped as they orbited the Moon. 

 But when you're in orbit, the whole 

 sky continually rises and sets for you. 

 For a permanent resident of the Moon's 

 far side, though, Earth sits forever out 

 of sight. Visitors who want to pitch a 

 tent there yet still talk to their pals on 

 Earth will need to set up relay stations 

 just past the outer limits of the far side. 

 From there, Earth is low on the hori- 

 zon but fully visible — and ready for you 

 to phone home. 



The design of NASA's newest ro- 

 botic mission to the Moon, called 

 the Lunar Reconnaissance Orbiter, 

 just passed muster, and the craft is now 

 scheduled for launch in 2008. Within 

 a decade, Chinese and Indian robots 

 may be traversing the Moon. Within a 

 few more decades, ordinary citizens of 

 planet Earth may be doing so as well. 

 The early trips, which will launch from 

 Earth with just enough speed to coast 

 to the Moon, will take about three 

 days; with continuous-thrust engines, 



38 na iurai HISTORY April 2006 



there's no telling how quick the later 

 ones could be. 



Although earthlings certainly love 

 the place, the Moon is not the sole 

 satellite of our affections, and we in- 

 tend to send spacecraft to orbit, study, 

 and occasionally land on some of the 

 solar system's other moons as well. 

 Some of those objects, a few of which 

 might harbor life, have had vehicular 

 visitors already. Between 1995 and 

 2002 Galileo flew close to five of the 

 threescore moons of Jupiter — includ- 

 ing icy Europa, which it circled at such 

 close range that features as small as a 

 school bus (though no actual school 

 buses) showed up on camera. Since 

 2004 Cassini has been scrutinizing 

 many of the nearly fifty moons of Sat- 

 urn. On Titan, Saturn's largest moon, 

 rivers of liquid methane have carved 

 channels in the frozen surface; on 

 Enceladus, a smaller Saturnian moon, 

 jets are streaming out of the south po- 

 lar region, unequivocally signaling ge- 

 ologic activity. Pluto and its satellite 

 Charon are yet another destination: in 

 20 1 5 NASA's New Horizons spacecraft, 

 which left Cape Canaveral on January 

 19, 2006, should reach them. 



To adults of "a certain age," it was 

 not long ago that the moons of the so- 

 lar system were simply points of light: 

 you tallied them and then ignored 

 them, in favor of the planets they or- 

 bited. But the twin multiplanet Voy- 

 ager missions of the 1970s and 1980s 

 showed that no two moons of the so- 

 lar system are the same. Each has its own 

 geology, impact history, temperature 

 profile, and orbital dynamics. In the 

 minds of scientists and citizens alike, the 

 moons became worlds unto them- 

 selves. And just like Earth's moon, they 

 became destinations worthy of our 

 dreams and, of course, our missions. 



Astrophysicist Neil deGihsse Tyson is the 

 director of the Hayden Planetarium at the Amer- 

 ican Museum of Natural History. His Natural 

 History essay "In the Beginning" (September 

 200}) won the 2005 Science Writing Award 

 from the American Institute of Physics. An an- 

 thology of his Natural History essays will be 

 published this year by W.W. Norton. 



