Illustrates Herschel's Star Gages principle. 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.

Controls
1. Angle: directional angle for pointing the telescope (in degrees). The telescope is fixed within a given plane, so it can only rotate about a single axis.
2. d_max: an optional control that lets the user limit the distance at which stars are visible through the telescope. The distance unit is a stellar unit, which is the average distance between neighboring stars in the stellar system.

Star System Frame
1. This frame shows a 3D view of the star system as seen from the outside.
2. Star System Options Menu
3. Show All Stars in System: show all the stars in the system. Otherwise only the stars in the telescope's field of view are displayed. If all stars are shown, the stars in the telescope's field of view are highlighted (made larger and shown in red).
4. Show Cone for Telescope's Field of View: displays a cone that defines the telescope's field of view. Only stars within this cone are visible. The height of the cone is set by the d_max value (see above).
5. Show Boundary of Star System: shows the boundary of the region in which the stars of the system are found.

Visual Elements
1. White points: stars in the star system. If all stars are shown the those visible through the telescope will be highlighted.
2. Red/magenta points: stars visible through the telescope. Colors indicate which system is being shown: red for uniform, magenta for nonuniform.
3. Yellow cone: the region of space visible by the telescope.
4. Green grid: boundary of the star system.

Requirements:
* Java

The license of this software is Freeware, you can free download and free use this calculator software.