UNIVERSE 



Exoplanet Earth 



Wliat would Earth look like from deep space 

 if inquisitive aliens were scanning for planets? 



By Neil deGrasse Tyson 



W 



hether you pre 

 fer to crawl, 

 sprint, swim, 



or walk from one place 

 to another, you can en- 

 joy close-up views of 

 Earth's inexhaustible 

 supply of things to no- 

 tice. You might see a vein 

 of pink limestone on the 

 wall of a canyon, a lady- 

 bug eating an aphid on 

 the stem of a rose, a clam- 

 shell poking out of the sand. 

 All you have to do is look. 



Board a jetliner crossing a 

 continent, though, and those 

 surface details soon disappear. No 

 aphid appetizers. No clams. Reach 

 cruising altitude, around seven miles 

 up, and identitying major roadways be- 

 comes a challenge. 



Detail continues to vanish as you as- 

 cend to space. From the window of the 

 International Space Station, which or- 

 bits at about 225 miles up, you might 

 find London, Los Angeles, New York, 

 or Paris in the daytime, because you 

 learned where they are in geography 

 class. But at night their brilliant hghts 

 present only the faintest glow. By day, 

 contrary to common wisdom, with the 

 unaided eye you probably won't see the 

 pyramids at Ciiza, and you certainly 

 won't see the Great Wall of China. 

 Their obscurity is partly the result ot 



having been made from the soil and 

 stone of the surrounding landscape. 

 And although the Great Wall is thou- 

 sands of miles long, it's only about twen- 

 ty feet wide — much narrower than the 

 U.S. interstate highways you could 

 barely see from a transcontinental jet. 



Indeed, apart from the smoke plumes 

 rising from the oil-field fires m Kuwait 

 at the end of the First Persian Gulf War 

 in 1991, and the green-brown borders 

 between swaths of irrigated and arid 

 land, from Earth orbit the unaided eye 

 cannot see much else that's made by hu- 

 mans. Plenty of natural scenery is visi- 



ble, though: hurricanes in the 

 Gulf of Mexico, ice floes in 

 the North Atlantic, vol- 

 canic eruptions wherever 

 they occur. 



From the Moon, a 

 quarter million miles 

 away. New York, Paris, 

 and the rest of Earth's 

 urban glitter don't even 

 show up as a twinkle 

 (unless you build a large 

 telescope before you take a 

 look). But from your lunar 

 vantage you can still watch 

 major weather fronts move 

 across the planet. From Mars at its 

 closest, some 35 million miles away, 

 massive snow-capped mountain chains 

 and the edges of Earth's continents 

 would be visible through a large back- 

 yard telescope. Travel out to Neptune, 

 2.7 billion miles away — just down the 

 block on a cosmic scale — and the Sun 

 itself becomes embarrassingly dim, now 

 occupying a thousandth the area on the 

 daytime sky that it occupies when seen 

 from Earth. And what of Earth itself? 

 It's a speck no brighter than a dim star, 

 all but lost in the glare of the Sun. 



A celebrated photograph taken in 

 1 990 from the edge of the solar system 

 by the t oyiH^cr 1 spacecraft [sec plioto- 

 j^rapli oil pii'^c 55] shows how under- 

 whelming Earth looks from deep 

 space; a "pale blue dot," as the late 



NA7 URAI, HISTORY February 2006 



