SCIENCE PROGRESS 



THE GREAT STAR MAP 



By H. H. turner, D.Sc, D.C.L., F.R.S. 



Savilian Professor of Astronomy in the University of Oxford 



The simpler name *' star map " is here applied to the chart 

 generally known as the " Astrographic Chart," because this 

 latter conve3'S a suggestion of technicality which is absent from 

 the project. What astronomers in different parts of the world 

 are really about is the making of a large and much more 

 detailed map of the stars than has hitherto been produced. 

 The map is being made by photography ; but though the 

 word *• astrographic " has been coined for use when photo- 

 graphy is applied to the stars, the work does not involve 

 much technicality that is not familiar to the users of an 

 ordinary Kodak. In three details only does the work of the 

 astronomer differ from that of the amateur photographer : 

 he uses a much longer camera ; he drives the camera by 

 clockwork so that it may follow the stars ; and he takes 

 pictures at night instead of in the daytime. It may perhaps 

 be added that he uses the light emitted by the stars, instead 

 of photographing objects by the reflected light of the sun. 

 But of these details more presently. 



Let us first consider what is the nature of a map of the 

 stars, as this differs somewhat in character from the maps of 

 the earth's surface with which we are familiar. There is no 

 question of finding our way, no question of delimiting property, 

 no question of showing hills and valleys. A map of the stars 

 is of a more monotonous character, being practically limited to 

 showing the exact positions and the brightnesses of individual 

 points of light. Maps of the stars may differ from one another 

 in scale, in accuracy, and in completeness : in scale because we 

 may show two given stars separated on the map either by a 

 foot or by an inch, according to requirements ; accuracy will 



