66 ILLINOIS ACADEMY OF SCIENCE 



PAPERS BY MEMBERS 



A CELESTIAL SPHERE IN A NATURAL 

 HISTORY MUSEUM. 



WALLACE W. ATWOOD 



The Chicago Academy of Sciences has appreciated the 

 increasing interest in astronomy and the difficulty which 

 every one meets in trying to become familiar with even the 

 brighter stars, and more commonly known constellations. 

 Various plans for promoting this study were considered by 

 the Academy. The flat star charts are confusing to the un- 

 trained observer, and the globes, on the outside of which stars 

 are sometimes represented, are unsatisfactory. 



Through the use of the Celestial Sphere, now in the 

 Academy Museum, it is possible to become familiar with all 

 the constellations that are ever visible in the latitude of Chi- 

 cago. Few people have had the opportunity of seeing all of 

 these constellations for on a given evening it is possible to see 

 but a few of them and the apparent motion is so slow that it 

 would take hours and hours of careful watching to see all 

 of those visible on a single perfectly clear night. 



The stars of the first, second, third, fourth and a selected 

 number of those of the fifth magnitude visible from the alti- 

 tude of Chicago are represented in the Sphere, and the total 

 number is 692. In addition to the fixed stars, four planets, 

 Venus, Mars, Jupiter and Saturn are represented as well as 

 the Sun and Moon. The celestial equator is clearly marked 

 in the interior of the sphere, and the ecliptic, or apparent 

 yearly path of the Sun among the stars, is also shown. 



Many of the mathematical conceptions necessary for the 

 study of descriptive astronomy and which often discourage 

 the beginner, are made with this sphere, perfectly simple. 

 There is now no reason why any one, including the younger 

 school children, can not become familiar with the chief con- 

 stellations their apparent movement, the brighter stars and 

 the ireal and apparent movements of the Sun, Moon and 

 planets. 



Many of the fundamental ideas in mathematical geog- 



