DEVELOPMENT OF THE PLANETARIUM — CHAMBERLAIN 263 



Attached to the center of the ceiling of a room almost 40 feet in 

 diameter is the sun globe. It is about 10 inches in diameter and con- 

 tains a 300-watt light bulb which is the source of light for the entire 

 room. The planets Mercury, Venus, the earth, Mars, Jupiter, and 

 Saturn are represented by balls with diameters of from about 1.6 

 inches to about 8 inches. They move in orbits around the sun with 

 speeds proportionate to their natural velocities. The earth com- 

 pletes a year in about 12 minutes. 



The earth orientation derives from the carriage to which the earth 

 ball is attached, and which moves around with it. An observer rid- 

 ing in the carriage, seeing the planets through a periscope as lighted 

 by the "sun" against the constellations painted on the walls of the 

 room, can readily appreciate the similarity to nature's planet family. 

 In effect, he has seen an artificial sky that aims to reproduce the skies 

 as seen from the earth. Of course, all comparative sizes and dis- 

 tances are distorted, and only one observer at a time can be carried 

 on the earth carriage. 



Another type of planetarium gives a somewhat superior reproduc- 

 tion of the skies to a few more viewers. One of the oldest examples is 

 known as the Gottorp Globe. Finished in the 1660's, it was a sphere 



11 feet in diameter, weighing Sy 2 tons, and so constructed that about 



12 persons could enter it, stand on a platform within it, and see the 

 sky as viewed from the earth rather than from space beyond the 

 earth. The Gottorp Globe had a typical map of the sky on its inner 

 surface, and many stars were represented. Originally it was driven 

 by waterpower to rotate once every 24 hours. 



Roger Long, professor of astronomy at Cambridge, constructed an 

 "Astronomical Machine" in the eighteenth century which was quite 

 similar in basic design to the Gottorp Globe. Its interior platform 

 accommodated about 30 people, and the stars were represented by 

 holes punched into the 18-foot sphere. A light representing the sun 

 could be moved along the proper path to simulate the sun's motion. 



The twentieth-century version of these globes was constructed in 

 1911 for the Chicago Academy of Sciences after a design by Dr. 

 Wallace W. Atwood, president of Clark University. It was 15 feet 

 in diameter and electrically driven. Motions of both the sun and 

 moon could be demonstrated. 



Before the outbreak of World War I, Dr. Oskar von Miller, cre- 

 ator and director of the Deutsches Museum, approached the Zeiss firm 

 regarding the construction of a planetarium that would show the 

 movements of the heavenly bodies according to the Ptolemaic system 

 on the interior of a hemispherical dome in the same manner as they 

 appear to an observer on the earth. The first idea considered was to 

 represent the stars by small electric bulbs attached to the dome, which 



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