198 Trees, Stars, and Birds 



Andromeda. Andromeda is overhead at about nine 

 o'clock in the middle of November. It contains three 

 second-magnitude stars in a line extending east and 

 north from the northeast corner of the Great Square of 

 Pegasus. The star at the corner of the Square belongs 

 to both constellations. A line drawn from this star 

 to Polaris and extended beyond it will strike the Great 

 Dipper near where the handle joins the bowl. 



Perseus. Perseus is high in the sky at the beginning 

 of the year. It may be recognized by stars arranged in 

 the form of a hook, or somewhat like the letter J. The 

 brightest of them, Alpha, is 40 degrees from the North 

 Star in a direction opposite to that of the bowl of the 

 Little Dipper. This curved line of stars forms only a 

 part of the constellation Perseus. Beta Persei, which is 

 the next to the brightest star in the constellation, does 

 not form part of the J but lies about 9 degrees south and 

 a little west of Alpha. 



A variable star. Having found Beta Persei, which is 

 also called Algol, you will be interested to know some- 

 thing about it, for it is a wonderful star. For 60 hours 

 it continues to be of the second magnitude and to 

 show no change in brightness. Then it grows dimmer, 

 losing about five sixths of its light. In less than 5 hours 

 after obscuration starts, it begins to brighten again, and 

 in 3 1 hours more it is as bright as ever. 



This change in brightness is explained by supposing 

 a dark or faint companion to pass in front of it and partly 

 eclipse it, the period of revolution being about 68 hours, 

 49 minutes. Although no companion can be seen, we 

 feel sure that this explanation is correct, not merely 



