detect. And nowhere is this need more 

 evident than in the construction of a 

 radio telescope. 



Radio telescopes, the earliest non- 

 visible-light telescopes ever built, 

 are an amazing species of observatory. 

 The American engineer Karl G. Jansky 

 built the first successful one between 

 1929 and 1930. It looked a bit like the 

 moving sprinkler system on a farmer- 

 less farm. Made from a series of tall, rec- 

 tangular metal frames secured with 

 wooden cross-supports and flooring, it 

 turned in place like a merry-go-round. 



named Grote Reber, from Wheaton, 

 Illinois, built a thirty-foot-wide, metal- 

 dish radio telescope in his own back- 

 yard. In 1938, under nobody's employ, 

 Reber confirmedjansky's discovery, and 

 then spent the next five years making 

 low-resolution maps of the radio sky. 



Reber's telescope, though without 

 precedent, was small and crude 

 by today's standards. Modern radio tele- 

 scopes are quite another matter. Un- 

 bound by backyards, they're sometimes 

 downright humongous. MK 1, which 

 began its working life in 1957, is the 



The first radio telescope looked 







like the mobile sprinkler system 



t ■ *i *if 





on a farmeries s farm. 



1 4 J 



Jansky had tuned the hundred-foot- 

 long contraption to a wavelength of 

 about fifteen meters, corresponding to 

 a frequency of 20.5 megahertz. Jansky s 

 agenda, on behalf of his employer, Bell 

 Telephone Laboratories, was to study 

 any hisses from Earth-based radio 

 sources that might contaminate terres- 

 trial radio communications. 



The result of Jansky s labors, "Elec- 

 trical Disturbances Apparently of Ex- 

 traterrestrial Origin," appeared in Pro- 

 ceedings of the Institute for Radio Engi- 

 neers in 1933. By spending a couple of 

 years painstakingly tracking and tim- 

 ing the static hiss that registered on his 

 jerry-rigged antenna, Jansky had dis- 

 covered that radio waves emanated not 

 just from regional thunderstorms but 

 also from the center of the Milky Way. 

 That region of the sky swung by the 

 telescope's field of view every twenty- 

 three hours and fifty-six minutes: ex- 

 actly the period of Earth's rotation in 

 space and thus exactly the time need- 

 ed to return the galactic center to the 

 same angle and elevation on the sky. 



With that observation, radio astron- 

 omy was born — minus the radio as- 

 tronomers. Jansky was retasked within 

 Bell Labs and did not pursue the fruits 

 ofhis own seminal discovery. Four years 

 later, though, a self-startinu; American 



planet's first genuinely gigantic radio 

 telescope — a single, steerable, 250-foot- 

 wide, solid-steel dish at the Jodrell Bank 

 Observatory near Manchester, Eng- 

 land. A couple of months after MK 1 

 opened for business, the Soviet Union 

 launched Sputnik 1, and Jodrell Bank's 

 dish suddenly became just the thing to 

 track the little hunk of orbiting hard- 

 ware — making it the forerunner of to- 

 day's Deep Space Network for tracking 

 planetary space probes. 



Another variety of radio telescope, 

 the interferometer, comprises arrays of 

 identical dish antennas, spread across 

 swaths of countryside and electronical- 

 ly linked to work in concert. The re- 

 sulting signal is a single, coherent, high- 

 resolution image of radio-emitting cos- 

 mic objects. Although "supersize me" 

 was the unwritten motto for telescopes 

 long before the fast-food industry co- 

 opted the slogan, recent radio interfer- 

 ometers form a jumbo class unto them- 

 selves. They include the Very Large Ar- 

 ray, with twenty-seven eighty-two-foot 

 dishes positioned on tracks crossing 

 twenty-two miles of desert plains near 

 Socorro, New Mexico; the Very Long 

 Baseline Array, with ten eighty-two- 

 foot dishes spanning 5,000 miles from 

 Hawai'i to the Virgin Islands; and the 

 Giant Metrewave Radio Telescope, 



thirty 148-foot lightweight mesh dish- 

 es spanning sixteen miles of arid plains 

 east of Mumbai, India. In the past dec- 

 ade, those engineering marvels have un- 

 veiled stunning phenomena in our own 

 galaxy. One, announced this past Feb- 

 ruary, is a young star 500 light-years 

 from Earth that's ringed by an inner disk 

 of dust orbiting one way and an outer 

 disk orbiting the opposite way. Anoth- 

 er is a pulsar speeding out of our galaxy 

 fast enough to travel from New York to 

 London in five seconds. 



And just wait until the sixty-four an- 

 tennas of ALMA, the Atacama Large 

 Millimeter Array, start observing from 

 the remote Andes of northern Chile. 

 Tuned for microwaves, whose wave- 

 lengths (the second longest, after radio 

 waves) range from fractions of a milli- 

 meter to several centimeters, ALMA 

 will give astrophysicists high-resolution 

 access to categories of cosmic action un- 

 seen in other bands. ALMA's location 

 is, by intention, the most arid landscape 

 on Earth — three miles above sea level 

 and well above the wettest clouds. Wa- 

 ter may be fine for microwave chefs but 

 it's bad for astrophysicists, because the 

 water vapor in Earth's atmosphere 

 chews up pristine microwave signals 

 from across the galaxy and beyond. 



All those (and other, yet-to-be- 

 built) arrays will give astrophysicists a 

 strikingly better look at known objects 

 and phenomena. In addition, the ar- 

 rays will help answer some big out- 

 standing questions, such as what dark 

 matter is made of, what dark energy 

 might be, and how galaxy clusters have 

 evolved since birth. Testing the funda- 

 mental tenets of Einstein's general rel- 

 ativity is also in the cards. 



At the ultrashort- wavelength end of 

 the electromagnetic spectrum are 

 high-frequency, high-energy gamma 

 rays, whose wavelengths are measured 

 in picometers. Discovered in 1900, they 

 were presumed as early as the 1940s to 

 be of cosmic origin. But no one actu- 

 ally detected them from space until a 

 new kind of telescope was placed aboard 

 NASA's Explorer XI satellite in 1 961 . 

 Anybody who's watched too many 



NATURAL HISTORY June 2006 



