Mapping the Milky Way: William Herschel's Star-Gages

Abstract

In 1785 astronomer William Herschel mapped out the shape of the Milky Way star system using measurements he called "star-gages." Herschel's star-gage method is described in detail, with particular attention given to the assumptions on which the method is based. A computer simulation that allows the user to apply the star-gage method to several virtual star systems is described. The simulation can also be used to explore what happens when Herschel's assumptions are violated. This investigation provides a modern interpretation for Herschel's map of the Milky Way and why it failed to accurately represent the size and shape of our galaxy.