Herschel's Star Gages


General Description

This simulation illustrates William Herschel's methods of "star-gages" by which he attempted to map out the shape of our galaxy in 1785. Herschel's star gages (sic) relied on two important assumptions: that Herschel's telescope (his "large 20 foot" with an 18.5 inch aperture) could see to the ends of the galaxy, and that within the galactic system stars are distributed uniformly. If the first assumption holds then the stars seen in the telescope all lie within a conical region of space with the apex at the telescope and the base at the edge of the galaxy. If the second assumption holds then the number of stars seen in the telescope is proportional to the volume of this cone. Since the volume of the cone is proportional to the cube of its height, the distance to the galactic edge in any direction is proportional to the cube root of the number of stars seen in that direction.

This simulation allows the user to use Herschel's method of star gages to map out the shape of several artificial "star systems." One window shows the view through a telescope, with a slider to rotate the telescope around a fixed axis. Another window shows a 3D view of the star system, showing either all of the stars in the system or only those stars visible through the telescope. A third window shows a plot of the star-gages. Plotting star-gages for many different directions maps out a cross-section of the star system. An optional slider allows the user to limit the distance at which stars are visible, and a menu allows the user to select from six different stars systems (some with stars distributed uniformly, others with non-uniform distributions). These options let the user explore how violations of Herschel's two fundamental assumptions invalidate his star-gage method.


Telescope View Frame

This frame shows the view through a telescope looking out from within the star system.

Star System Frame

This frame shows a 3D view of the star system as seen from the outside. The viewing angle can be changed by clicking and dragging within the viewing panel.

Star Gage Plot Frame

This frame shows a plot of the star gage results. Plotting the star gages for a variety of angles will map out a cross section of the star system, if Herschel's assumptions are valid.
Todd K. Timberlake (ttimberlake@berry.edu)