sci-fi movies knows that gamma rays are 

 bad for you. They're also hard to trap, 

 because they pass right through lenses 

 and mirrors. How, then, to observe 

 them? The guts of Explorer XTs tele- 

 scope held a device called a scintillator, 

 which responds to an incoming gamma 

 ray by pumping out electrically charged 

 particles. By measuring the energies of 

 the particles, you can tell what kind of 

 radiation created them. During the four 

 months that Explorer XI tumbled 

 through space, its telescope gathered 

 data for twenty-three days and snared 

 twenty-two certified gamma-ray hits. 



Two years later the Soviet Union, the 

 United Kingdom, and the United 

 States signed the Limited Test Ban 

 Treaty, which prohibited nuclear test- 

 ing in the atmosphere, in space, and 

 underwater. The Cold War was on, and 

 so, to monitor the Soviets, the US. de- 

 ployed a new series of satellites, the I c- 

 las, to scan for the invisible light that 

 would result from aboveground nuclear 

 tests. What the satellites found instead 



were almost daily bursts of gamma rays, 

 later shown to be the calling card of dis- 

 tant stellar explosions. 



During the 1990s NASA began its 

 Great Observatories program: four 

 state-of-the-science spaceborne tele- 

 scopes, each covering a chunk of the 

 electromagnetic spectrum that does not 

 fully penetrate, or is otherwise altered 

 by, Earth's atmosphere. The first was the 

 Hubble Space Telescope, which detects 

 primarily visible and ultraviolet light. 

 The second, which operated until June 

 2000, was the Compton Gamma Ray 

 Observatory. The third and fourth — the 

 Chandra X-Ray Observatory and the 

 Spitzer Space Telescope, for infrared — 

 are, like the Hubble, still operating. As 

 for radio telescopes, the big ones don't 

 fit into contemporary spacecraft. Fortu- 

 nately Earth's atmosphere is transparent 

 to most radio waves, so radio telescopes 

 needn't be spaceborne to do good work. 



While still taking data, the Compton 

 Observatory saw something as unex- 

 pected as the Velas discoveries: gamma 



rays right near Earth's surface. Turns out, 

 as is evident from the fact that you're 

 reading this sentence, that not all bursts 

 of gamma rays are equally lethal [see 

 "Knock 'Em Dead," by Neil deGrasse 

 Tyson, May 2005], nor are they all of 

 cosmic origin. In fact, a team of gam- 

 ma-ray sleuths recently concluded that 

 at least fifty bursts emanate daily near the 

 tops of thunderclouds, a split second be- 

 fore ordinary lightning bolts strike. 



Despite all the mind-blowing dis- 

 coveries made at nonvisible 

 wavelengths, visible-light instruments 

 still have the power to shock and awe. 

 In September 2005, astrophysicists us- 

 ing the Visible Multi-Object Spectro- 

 graph of the European Southern Ob- 

 servatory's Very Large Telescope array 

 announced they had found a group of 

 galaxies some 13.5 billion light-years 

 from the Milky Way. A more distant 

 object has never been seen. Nothing 

 has ever been observed from so long 

 ago, mere moments after the beginning 

 of what we all know as time. 



Yearning to see the universe for what 

 it is — a stupendously rich collection of 

 objects and phenomena waiting to be 

 understood — today's astrophysicists 

 have armed themselves with telescopes 

 strategically positioned across the elec- 

 tromagnetic spectrum. Newton wasn't 

 thus equipped. In thirty-one unan- 

 swered Queries appended to later edi- 

 tions of his Opticks: Or, A Treatise of the 

 Reflections, Refractions, Inflections and 

 Colours of Light, first published in 1704, 

 he deeply pondered the unexplained na- 

 ture of nature. At the end of Query 25 

 he asks "whether the Rays have not 

 more original Properties than are yet dis- 

 cover'd." Comprehensive though it was, 

 Opticks explored only the visible spec- 

 trum. Little could Newton have known 

 how many more Properties were as yet 

 undreamt of in his philosophy. 



Astrophysicist Neil deGmsse Tyson is the 

 director of the Hoyden Planetarium at the Amer- 

 ican Museum of Natural History. An anthology 

 of his Natural History essays, Death by Black 

 Hole: And Other Cosmic Quandaries, mil 

 he published this year by W.W. Norton. 



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• The optics of jomirascope 

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How to order 



You may order by toll-free phone, by mail, or 

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jomira 



division of jomira/advance 



47(1 Third Street, #211, San Francisco, CA 94 1 07 



26 



NATURAL HISTORY June 2006 



Order by toll-free phone: 1-800/600-2777, or (fastest!) by fax: 1-415/356-7804. 

 Visit our website at www.jomira.com 



