Sun Compass for Palm Palm OS Treo, Tungsten software and freeware downloads

Version 1.8: GeoFinder support for over 125,000 city locations worldwide. Look for the GeoFinder freeware application for details. With multilingual interface: Now available in english, german (Deutsch), italian (Italiano), dutch (Nederlands) and spanish (Español). This program is a compass for Palm handhelds. All you have to do, is to setup your home city by selecting it from the list. If your hometown is not available just select one nearby.

After knowing the geographic position (longitude and latitude) and the timezone (difference to the GMT Standard Time) the program calculates the direction of the sun and displays a yellow circle (sun symbol) on the display.

Installation:
Install the SunCompass.prc on your Palm. In this version the runtime is already included in the PRC-File. The only library you have to install ist the Mathlib Library (MathLib.prc - included in the archive). If you want to install Sun Compass on your SD- or MM-Expansion Card just do it. But: The mathlib-library has to be installed in RAM.

Sun Compass itself is Freeware. Feel free to distribute it wherever you want, but please let me know the URL.

For putting it on CDs or DVDs please definitly ASK me.

How to use this app

1. Choose the city by taping the name in the lower right corner and selecting it from the dialog.
2. If you actually have a daylight saving time, check the checkbox.
3. Hold your Palm horizontal and rotate it until the sun symbol points to the direction of the sun.
4. Your compass is now aligned.

How the Sun Compass works, and what the time in the upper right corner of the screen means:

The position of the sun in the sky is described by its altitude (height above the horizon, in degrees of angle), and by its azimuth (direction to the point on the horizon directly below the sun, in degrees of angle from north). If you know the sun's azimuth, you can orient your compass layout to that direction, and it will then correctly indicate the directions of north, south, east, west, etc. The Sun Compass calculates and indicates the sun's azimuth on the compass layout so you can orient it correctly.

In order for the Sun Compass to calculate the azimuth, it must know your position (latitude and longitude) and the local apparent solar time. It estimates your position based on the known latitude and longitude of the city location you select. It estimates solar time from the clock time on your Palm (standard time for your time zone), and from your longitude.

Local apparent solar time is only the same as your standard time if you are located on the standard meridian for your time zone. (The meridian is the north/south line of longitude on the globe that passes through your location.) The standard meridians are established at every 15 degrees of longitude. For example, the standard meridian for the MET time zone (e.g. Munich, Germany) is 15 degrees east of the prime meridian (Greenwich, England) , and the standard meridian for the Central US time zone (e.g. Austin, Texas) is 90 degrees west. When you are located on the standard meridian for your time zone, the sun will be directly overhead at noon. But, if you are east of that meridian, the sun will pass directly over your location a few minutes earlier than 12 noon on your clock. If you are west of the standard meridian, the sun will be overhead later than clock noon.

For example, in Munich, the longitude is 11 degrees east, which is 4 degrees west of the standard meridian for that time zone (15 degrees east). It takes the sun 4 minutes to traverse 1 degree of longitude, so in Munich the sun passes directly over head 16 minutes after standard time noon, or at 12:16 pm. On your Sun Compass screen, the standard time for your time zone is shown on the upper left corner. The local apparent solar time for your location, which is the standard time plus/minus the correction for your longitude, is shown on the upper right corner.

Why does it take 4 minutes for the sun to traverse 1 degree of longitude? Simple. It takes 24 hours for the sun to traverse all 360 degrees of longitude around the planet in a single day. That's 24 hrs x 60 minutes/hr, or 1,440 minutes in a day. Divide 1,440 minutes by 360 degrees, and you find it's 4 min/deg.

Another detail that the Sun Compass needs to take care of is daylight savings time. If you are located in a place which uses daylight savings time, your clock time is increased by one hour during the summer. The calculation needs to subtract that hour from the clock time before the correction for local apparent solar time can be made.

A final correction that the Sun Compass calculates is a bit more esoteric. It accounts for the fact that the earth's speed in its orbit around the sun is not constant, due to the eliptical shape of the orbit. As a result, at some times during the year local apparent solar noon is a few minutes early, and at other times it's a few minutes late. The so-called "equation of time" is applied to make this correction.

Note: Notwithstanding the sophistication of the Sun Compass algorithms, you should understand that the accuracy of the compass is not high. It depends primarily on how closely you can align your Palm with the sun, and on how well you succeed at pointing to the direction you want to travel. It's a lot better, however, than looking at the moss growing on the side of a tree, estimating the direction of jet contrails, sniffing the breeze, or any of the other rough and ready methods people use to guess directions ;-).

Thanks to Douglas Mahone for that explanation!

The Sun Compass is freeware, so I unfortunately cannot do intensive support. Hope you understand that.