ASTRONOMICAL SECTION 



A GREAT TRIPLE SUN 



Recent Researches in the Gigantic Stellar System of Lambda Tauri 

 Wm. H. Knight 



THIS noble object, an eclipsing variable, is to the unaided vision a 

 star of the third magnitude, just below the Hyades in the constel- 

 lation Taurus. The great red star Aldebaran, recognized as the angry 

 eye of the Bull, is at the top of one stem of the letter "V," which 

 forms the Hyades group. It is worth while to note that Lambda 

 Tauri is, next to Algol, the most conspicuous eclipsing variable in 

 the heavens. 



This interesting star has long been an object of earnest inquiry, 

 for its normal brightness is diminished by two minima. That is, 

 its light wanes with unceasing regularity once in about four days; 

 to be exact, at the end of every 3.95 days. The decrease is not much, 

 but it is as invariable as the succession of day and night on our globe. 

 The cause of this diminution of light was an insoluble mystery 'till 

 the spectroscope in the hands of Belopolsky at the Pulkowa Observ- 

 atory in 1897 showed that this fine star, a single point of light in the 

 most powerful telescope, consists of two mighty suns revolving round 

 a common center of gravity with enormous velocity, the plane of the 

 orbit being presented nearly on edge to our vision. 



At each revolution the smaller of the two bodies, known as the 

 companion, and less bright than its primary, passes between the 

 observer and the primary, partially eclipsing it, and thus causing a 

 diminution of the light of the two bodies. This is a rational and 

 satisfactory explanation of the four-day phenomena. 



But the behavior of Lambda Tauri is complicated by another and 

 less notable minimum which occurs once in thirty-four days. It is 

 as insistent as the four-day period, but less pronounced in the dimi- 

 nution of light. How to account for that has been the puzzle, but a 

 satisfactory explanation has recently been offered by Schlesinger of 

 the Allegheny Obesrvatory. He assumes that there is a smaller body 

 revolving round the gigantic binary in a period of thirty-four days, 

 and this body, passing between the eye and the binary every thirty- 

 fourth day, would fully account for the slight but unfailing diminu- 

 tion of light observed. Is not that a striking case of "the astronomy 

 of the invisible" asks Joel Stebbins of the Illinois Observatory, who 

 has been making a study of this interesting variable. 



And now the question arises, what are the dimensions of these 

 great suns, so far out in the depths of space that no astronomer has 

 been able to measure their parallax? Spectrum analysis again comes 

 to our assistance and furnishes a solution. This Rosetti stone of 

 astronomical science shows the velocity of the approach or recession 

 of a star in the line of sight. Knowing that velocity we measure the 

 dimensions of the orbits traversed by the two suns, and thence make 

 an approximate estimate of the bodies moving in those orbits. 



The dazzling splendor of the two bodies forming the eclipsing 



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