NEWS FROM THE STAES. 



By C. G. Abbot, 

 Director, A!iiroi)hijsic(il Ohscrvatori/, f^mithsoniari rnstitution. 



[With 5 plates.] 



Light is the messenger that brings the news. The message is in 

 cipher, very long, faint, and hard to read. It tells of the materials, 

 classification, temperatures, motions, distance, grouping, brightness, 

 variability, mass, size, and number of the stars. 



IIATERIALS. 



Starlight collected by a telescope is passed through a spectroscope. 

 This forms a narrow band, called the spectrum, violet at one end, 

 red at the other. A photograph of the spectrum is made, and for 

 most stars this shows the band of colors crossed by dark lines. 



Suppose an electric arc is made to play between iron poles, and 

 its light is sent through the spectroscope. Instead of a bright con- 

 tinuous spectrum with darJc lines, as given by a star, there appears 

 its exact opposite — a very faint spectrum crossed by hright lines, 

 especially numerous where the green occurs in the spectrum of star- 

 light. 



Matched together, one spectrum above the other, the bright iron 

 lines occur where the dark lines cross the star spectrum. So unmis- 

 takably is one the reversal of the other that the coincidence seems 

 to give proof of the presence of iron in the star. Probability be- 

 comes assurance when it is laiown that under some circumstances 

 iron vapor can produce darh lines on bright spectrum ground, just 

 as usually foimd in starlight, and that some stars, on the other hand, 

 show hright lines on a faint spectrum background. 



Hydrogen, helium, oxygen, calcium, and many other elements are 

 similarly shown to exist in the stars by spectroscopic examination of 

 starlight. But not all the stars show all these elements. Great dif- 

 ferences are found in the stellar spectra, and stars are classified 

 accordingly. 



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