Satellite Altimeter

This is not seriously technical, but it is a fun project to entertain onlookers while you are seriously engaged in satellite observing.  Using the pictured device and a stopwatch, or a wristwatch with a stopwatch feature, you can get a rough idea of a satellites altitude by timing its passage through an arc.

The device (altimeter) is nothing more than a means to measure the arc.  Two pieces of cardboard are glued together for stiffness and then cut in the shape of a trapezoid.  Two sets of toothpicks are poked into the cardboard so that when they are lined up a 30 degree arc can be measured.


The trapezoid shape is necessary so the altimeter can rest on the observers cheek at just the right distance from the eye to line up both sets of toothpicks simultaneously.  With a little practice, the observer can place the altimeter in front of a passing satellite and start the watch as the satellite passes the first pair of toothpicks.  Stop the watch when the satellite passes the second pair of toothpicks taking care to hold the first pair of toothpicks steady at the starting location.  It is also desirable to have the satellite pass through its highest point at the center of the 30 degree arc measurement.

After the satellite passage is timed, a quick look at the table on the altimeter will give the satellites approximate height.  This table happens to be printed in miles.  For example:  If it takes a satellite 40 seconds to pass through the 30 degree arc, the satellite is approximately 352 miles above the observer.  The background math is found here.  You can configure your altimeter to display any other unit system.