
New Planet Gnomon
General Description
This program simulates the shadow cast by a gnomon over the course of
a day for any day of the year on a fictitious planet. The user can
select from three different locations on the planet. The model is
constructed on the basis of a circular planetary orbit with the Sun at
the center (or, equivalently, a circular orbit for the Sun with the
planet at the center). The user can make measurements to determine
the latitude and relative longitude of all three locations. Since two
of the locations have the same longitude, the user can determine the
radius of the planet if given the distance between these two
locations. The user can also determine the obliquity of the ecliptic,
the number of hours in a solar day, the number of solar days in a
tropical year, the dates of the solstices and equinoxes, and the
latitudes for the arctic/antarctic circles and the tropics.
Gnomon Frame
- Options Menu
- Show North: show an arrow pointing North.
- Show Alt vs. Day Plot: displays a plot of the
Sun's altitude versus the day of the year.
- Show Alt vs. Time Plot: displays a plot of the
Sun's altitude versus the time of day (in hours).
- Location Menu: allows the user to select from three
different locations on the planet.
- Visual Elements
- Green plane: the horizon plane.
- Red line: the gnomon, which is aligned perpendicular to the horizon plane (ie vertical).
- Thick black line: the shadow cast by the gnomon.
- Orange sphere: the Sun.
- Magneta arrow: points due North.
- Orange line: line from the Sun to top of gnomon to tip of shadow.
- Controls
- Play/Pause: start and stop the simulation.
- Reset: reset simulation to original state.
- Clear Traces: clear all traces.
- Time: time of day, measured in hours from an
arbitrary starting time. Controls include a slider
and a step button that advances time by 0.1 hours.
- Day: day of the year, measured from an arbitrary
starting day. Controls include a slider and a step
button that advances time by one day.
- Alt: the altitude of the Sun in degrees (displays
0 if the Sun is below the horizon).
Version History
- Version 1.0 (2 Jul 2013): this program is a modified version of
Gnomon which uses data for a fictitious planet and limits
some of the functionality of the Gnomon program.
Todd K. Timberlake (ttimberlake@berry.edu)