Clever concept well-presented

The best of the sun compasses in app store. Cousin to sundials, a sun compass does require a certain level of understanding: Sundials use a known compass orientation + the current location of the sun to solve for the time. Sun Compasses use a known time + the current location of the sun to solve for compass orientation. In the case of the Sun Compass app, the app supplies the time, and you indicate to the app the location of the sun, deriving in the process the proper orientation of the compass. (If you open the app several times during the day, you will see that the positions of the sun and moon are moving, very slowly, over time.)

The best and safest way to use this app is to place the iPhone on a flat horizontal surface. Then hold, with one hand, a stylus so that it rises vertically from the very center of the compass rose. This will cast a shadow exactly opposite the physical suns position. Then, with the other hand, touch the sun (the one on the iPhones screen!) and rotate it until its shadow line lines up with the physical shadow you are casting. By coordinating the virtual shadow with the physical shadow, you have done the necessary work to rotate the compass into its proper alignment. You now have a compass that is displaying true (not magnetic) north.

Once you have touched the sun icon, you can slide your finger back off the icon out toward the edge of the screen without losing control of the suns movement. (Make sure you don’t lose contact with the screen in the process!) That can make it easier to shift that hand around without running into the other hand holding the stylus.

Sun Compass allows you to play the same trick at night, as long as the moon is out. What is lacking is a sighting point for moonless nights, something Celestial Compass offers with its display of the current location of the Big Dipper. Celestial Compass is otherwise is not as pleasant to use as Sun Compass, however.

Sun Compass, in my brief comparison tests, also showed the greatest accuracy of the lot. Whether the small level of error I did observe is due to my distance from the center of my particular time zone, I don’t know.

(Our modern time zone system replaced the older system where each town had it’s own time, clocked from when the sun passed directly overhead. Now, the only towns with accurate time are those that lie exactly on the center line of the time zone. If you live on either side, you are using a compromise time. This compromise can throw off a sun compass by several degrees.)

99 cents for a sanity-check backup to a GPS compass, probably a good investment. 99 cents for an afternoon with the kids, teacing them about sun compasses and sundials in a fun, engaging way, definitely a good investment.

Asktog about Sun Compass