Star-Tracker: Learning About Earth, Space, and Time

By Richard A. Strong, B.Sc., Astronautical Engineering (Major,USAF,Retired)

You can download the * Star-Tracker booklet in MS Word (1.4 mb)

	
BACKGROUND AND INTRODUCTION

	The authors recall how it all began. Richard was instructing 
Air Force pilots about how to fly in a simulator by referring to the 
instruments. He was puzzled when several pilots descended below their 
target altitudes. The pilots were misreading their altimeters that had 
three pointers. Years later, he was performing duties as a system 
engineer and analyzed the problem. He designed an altimeter dial with 
offset numbers and zones to eliminate the problem. 

	Richard’s wife, Rosa Maria, was teaching in elementary school 
classrooms; he showed the new dial face design to her and explained 
how it solved the problems. She studied it and remarked that it would 
be good for teaching her students how to read clocks. They worked 
together and designed the clock dial-faces. Then they added in the 
24-hour dial-faces, which they named “Star-Trackers”. They made some 
clocks with the new dial faces. Then they taught their four children 
and Rosa’s students with the new dial-faces and found that they liked 
them and read them easily. The system was described in a booklet that 
was distributed to many schools. This activity took place in the 1970’s 
when 24-hour clocks and wristwatches were difficult to obtain. 

Rosa enjoys being retired as an elementary school Principal and Richard 
enjoys being retired from 44 years of government service. He holds a 
Commercial Pilot license and spends his time designing flyable automobiles 
and maintaining his website, www.strongware.com.
  
You can learn about your earth, space, and time by seeing and 
using the Star-Tracker clock dial design. You can print the dials, 
cut out center holes, and affix them to your clocks. 
Two designs are presented: 
The main design is for a clock that has the International 
24-hour movement * 24-hour face ; 
the second design is for the standard 12-hour movement 
* 12-hour face .

(The graphic may look elliptical, but you can print it and see that it's circular.)

   A feature of the Star-Tracker dials is the "Dyna-Zone" system. 
Instead of the confusing technique of displaying a specific point 
to indicate a specific time, a zone is used to indicate a time interval. 
Therefore, a reader need only look at the hour hand and see the zone 
that it is pointing towards and then so with the minute hand and 
have  a digital read-out, just as one would say the time. 
    This eliminates the common problem of misreading the time when 
the minute hand is pointing on the left side of the dial so that 
the hour hand points to the next hour, rather than the current hour. 
    The design also shows arrowheads to show the direction of time. 
Studies in detail show that the task of reading the time actually 
requires 17 steps. Classroom demonstrations have proved the 
superiority of this technique.
  You may notice that the good old U.S.A. is the only country that 
still hangs on to the 12-hour system that was based on the ringing of 
church bells ( apparently, folks lost track after 12 chimes). 
While many think that the 24-hour system is military ( "Zulu Time"), 
it's really scientifically-based on Coordinated Universal Time 
(not "Greenwich Mean Time"), or "CUT".
   You can setup your 24-hour main design clock so that it faces 
to North and you look South to read it. The hour hand will point to, 
or "track" the sun, that is a star, hence the name "Star-Tracker". 
Note that the hour hand still points to the sun even when it's below 
the horizon at night-time. 
	Notice that the circular hour pointer has sectors to show the 
seasonal variations of sunrise and sunset times.
	If you'd like to set up to track better, 
then you can tilt your clock southward so that the tilt from vertical 
matches your latitude, usually between 45 degrees for the northern U.S. 
down to about 27 degrees for the southernmost latitudes. 
	Notice that the hour hand is always aligned to the sun and the clock and 
the planet and everything on it rotates around its core axis. 
	After a while, you may overcome the false illusion that 
the Sun moves around the Earth and so realize the truth of the matter,
that is, that the Earth spins and we are moving eastwards at speeds of 
hundreds of miles every hour. 
	You can figure that dividing the longitude into time zones of 
15 degrees for each hour; this equals 15 x 60 longitude minutes for 
60 time minutes or 15 longitude minutes for each minute of time. 
If you figure that you're moving Eastward at about 600 miles per hour,
then you see that you're moving Eastward 15 longitude minutes every
minute of time, or one degree every four minutes. If you use the
Global Positioning System, you can relate to the longitude coordinates.
You can also understand why space launchers usually take off towards 
the East, such as from Cape Canaveral or near the Equator, 
such as the French launch sites, to take advantage of the natural velocity.
The exceptions to the rule are satellite launchers that wish to scan
the entire planet and use polar orbits and so launch to the South or
North. These orbits are fixed in space, similar to pendulums.

The st1.jpg cutout is a dial; you can fold the bottom plate underneath 
as a mounting stand and make a slit on the left side as indicated. 

The st2.jpg is the latitude gauge; you can cut it out, 
fold the bottom underneath, then insert it into the slit and glue the two 
bottoms together as shown in st3.jpg. 


*The st4.jpg shows how the latitude is to be matched by the tilt of the dial. 
You can cut out the hour and minute pointers and mount them with a common pin. 
Advanced users  may like to note the seasonal differences in the tilt, 
particularly at the solstices; this amounts to about 24 degrees above and below. 
Likewise, by measuring the time error, the longitude may be estimated. 
Latitude measures 15 degrees per hour, or, 3 degrees for every one-fifth of an hour. 
You can use the minute zones to estimate the fifths. As an example, 
if the sun lines up at noon with the :03 minute mark, showing the 
sun is "ahead" of the clock, then the longitude is 

degrees times 3 = 9 degrees more that the time zone longitude. 

For quick reference, New Orleans is at 75 degrees for Central Time, 
Los Angeles is at 120 degrees for Pacific Time.
The two dials are shown on the following pages. 
Note that you can use the 12-hour movement just like the 24-hour movement clock, 
except that the sun will be halfway between the hour hand and noon.

 
 
 


You can download the * Star-Tracker booklet in MS Word (1.1mb)

You can check out some 24-hour clock and wristwatch faces at:

http://www.aaawatchclub.com/24_hour_dial.html#1003b24pb ; and

http://www.officeclocks.com/cgi-bin/store/commerce.cgi?product=24_Hour_Clocks . 
 If you want to get the official time, WWV operates in the 
high frequency (HF) portion of the radio spectrum. 
The station radiates 10,000 W on 5, 10, and 15 MHz; 
and 2500 W on 2.5 and 20 MHz. 
Each frequency is broadcast from a separate transmitter.
check on http://tf.nist.gov/timefreq/stations/wwv.html
 One of the effects of our earth spinning is the coriolis force that 
makes tornados and hurricanes spin. If you're interested in learning about it, 
then read an explanation at

http://www.usatoday.com/weather/resources/basics/coriolis-understanding.htm

http://www.physics.ohio-state.edu/~dvandom/Edu/newcor.html