Sir Frank Dyson 93 



results. For instance, a star in Capella, hitherto shown 

 as single even by the most powerful telescopes, was broken 

 up and shown to be composed of two bodies revolving 

 around one another in a period of one hundred and four 

 days. The diameter of Betelgeuse has been measured 

 and found to be two hundred and fifteen million miles. 

 These figures will be better appreciated if we imagine 

 Betelgeuse in our sun's place. Then this planet would 

 be inside Betelgeuse and not half-way to its outer 

 surface. 



Not content with the one-hundred-inch reflector, the 

 Californian Institute of Technology is at present endea- 

 vouring to construct one of two hundred inches. This will 

 cost at least a million pounds, but if successful it should 

 add several hundred million more stars to those already 

 known ; yet even so it is unlikely to solve the problem of 

 whether Mars is inhabited. 



The largest telescope at Greenwich is of only thirty 

 inches aperture and is wholly devoted to the work of 

 photographing stars. Much is being done nowadays in 

 measuring the distances and temperatures of the stars. 

 You might suppose it was impossible even to guess at the 

 weight of a star lost in the depths of space, yet, as Sir 

 Frank Dyson pointed out, if you know the distance of a 

 pair of twin stars and their bulk, it is possible to calculate 

 their weight with considerable accuracy. Again, the 

 spectroscope enables astronomers to estimate the heat of 

 stars. The spectroscope is used to collect and analyse the 

 light collected by the telescope, and according to the pro- 

 portion of light at the blue or red ends of the spectrum 

 the heat of the star can be estimated. In brief, the 

 greater the degree of blue the hotter the star. 



In the Observatory are many photographs of the 

 spectra of stars, but the pictures of greatest interest to 

 the layman are those of solar eclipses, showing the 

 immense prominences or flames which appear on the edge 



