The Light Brigade 



"More light!" cried the poet Goethe just before he died. 

 For centuries, every sky watcher has said the same. 



By Neil deOrasse Tyson 



Astrophysicists are a proximity- 

 challenged lot. Most of the ob- 

 jects of our aff ection lie forev- 

 er out of reach and are, at best, barely 

 visible from Earth. They release stu- 

 pendous energy, are immune to ma- 

 nipulation, and don't grow in a labora- 

 tory. For the most part they are acces- 

 sible only by night. We can't easily visit 

 them in their natural habitat, and it's not 

 yet possible to touch them. In our study 

 of the contents and behavior of the uni- 

 verse, we deduce nearly everything 

 we know from the analysis of light. 

 Though smitten by the cosmos, astro- 

 physicists have no choice but to em- 

 brace it from multiple degrees of sepa- 

 ration: when we want to know the mo- 

 tions of a star, we examine not the star 

 itself, not an image of the star, not even 

 the spectrum derived from the light 

 recorded in an image of the star, but 

 rather the shifts in the patterns in the 

 spectrum derived from the light record- 



ed in an image of the star. It's a convo- 

 luted consummation, but it works. 



Clearly, astrophysicists need more 

 than eyes to accomplish these tasks. On 

 its own, the eye is a good detector but 

 not a great one — able to resolve visual 

 data no finer than about one-sixtieth of 

 one degree of a complete, 36( (-degree 

 circle. In the dark, the pupil expands to 

 about a quarter-inch across, and so it 

 registers only a fraction of the ubiqui- 

 tous light radiated by celestial bodies. 

 Visible light ranges in wavelength by 

 less than a factor of two, from 400 to 

 700 nanometers — a mere sliver of the 

 full electromagnetic spectrum. For 

 comparison, the wavelengths of the en- 

 tire spectrum range from less than half 

 a millionth of a billionth of an inch 

 (high-frequency gamma rays) to hun- 

 dreds of miles (extremely low frequen- 

 cy radio waves), a factor of more than 

 10,000 billion billion. Without a lot of 

 help, we'd never detect most of what 



exists and takes place even in the visi- 

 ble cosmos, let alone the multitudinous 

 happenings in all the nonvisible wave- 

 lengths of light. 



Serious help in seeing at a distance 

 arrived just four centuries ago, in 

 the form of a pair of cookie-size lenses 

 firmly fixed inside a tube and present- 

 ed in September 1 608 to Prince Mau- 

 rice of Nassau, Stadholder of the Unit- 

 ed Provinces of the Netherlands, by a 

 spectacle maker named Hans Lipper- 

 hey. His tube was the first historically 

 substantiated, honest-to-goodness tele- 

 scope, though allusions to earlier ones 

 abound. Within half a year Galileo had 

 learned of Lipperhey's indispensable in- 

 strument and had built a better one of 

 his own design. By the autumn of 1609 

 he was gazing at the Sun, Moon, plan- 

 ets, and stars. He was about to show that 

 Copernicus was right: the planets and 

 their moons do indeed revolve around 



18 



NATURAL HISTORY March 2006 



