The cross-staff was used systematically until telescopes with measuring instruments became standard. A cross-staff is easy to construct, and teens can learn both from its construction and its use.

PURPOSE: To determine HOW MANY DECREES OF ARC -- OR FRACTIONS OF A DEGREE -- IS A "TEST" STELLAR "BODY" FROM A KNOWN STELLAR BODY.

The best starting equipment is a printer's yarstick, which is 36 inches long, as with conventional yeardsticks, but calibrated in DEGREES OF ARC INTEAD OF INCHES.

Since you may have difficulty in finding this stick, I'll tell you how to construct its equivalent. Cut, or find, a piece of flexible clear plastic to the shape of a yardstick. It is 36 inches long, but you wish to render this as 180°. A simple division, 180/36 = 5, shows that 1 inch = 5 °. 3/16 inch = 1 °. Subdividing an inch into 5 equal intervals is a little difficult, but you won't need more accuracy in your sky-watching.

Cut or obtain a dowel to the length of a yard. Use it as a radius to sweep out a circle on the floor or on a table or on the blackboard, marking by chalk. You intension is to BOW THE PLASTIC TO THIS HALF-CIRCLE. CUT NOTCHES IN EITHER END OF PASTIC. USE KNOTTED CORD STRETCHED BETWEEN THESE ENDS (BOWED ALONG THE HALF-CIRCLE) TO FIX THE PLASTIC IN THE HALF-CIRCLE SHAPE.

FASTEN THE CENTER OF THE PLASTIC TO THE DOWEL, TO COMPLETE THE CROSS-STAFF.

At night, when you shine a flashlight on the plastic, you can read the degrees involved in your measurements.

Beginning with the familiar "Pole Star (a.k.a. North Star)", you may (with sufficient patience and proper methodology) ,I>survey the sky for stars of the first three or four magnitudes (easiest to see), and draw your own celestial map.

Good surveying!

(You may be interested to know that this is or was a standard item in the curriculum of Russian students.)