AstroMedia: The Pendulum Quadrant

AstroMedia: The Pendulum Quadrant

The quadrant is an astronomical instrument known since Babylonian antiquity. It shows, with the help of a plumb bob, the angle between the rays of sight to a pointed point, e.g. a star, and the horizon point directly below it. One speaks then of the (angular) altitude or the elevation angle of this point or star. Thanks to a transversal division of the scale, the measurement succeeds to an accuracy of about 10 arc minutes. It is equipped with a sounding pipe and handle. This simple device is the historical predecessor of Jacob´s staff and sextant.

How to measure
You determine any point in the sky (except the sun!) or in the landscape by taking a bearing on the point through the tube. While doing this, keep the plumb line on the quadrant. There, where the thread runs over the degree scale, you can read the angle.
Very important: Never take a direct bearing on the sun! This can cause irreparable damage to your eyes!
If you still want to determine the altitude of the sun, this can be done as follows: Point the right end of the dipstick at the sun and hold the other end close over an inclined surface that catches the shadow of the quadrant, e.g. your palm. Then rotate the quadrant until its shadow has become a line and the sun can shine through the dipstick unobstructed. Now the plumb line shows the angular height of the sun on the degree scale.

For teachers and students
The pendulum quadrant is easy to build and is an excellent teaching aid for secondary schools. Like all other astro materials, it can also be used for other group and project work on astronomy and physics.

This is what else you will need for assembly

a solid, flat work surface

a sharp cutter knife

a good all-purpose glue

some fine sandpaper

a pair of scissors

a solder, e.g., a bead, button, coin, or small stone

needle and thread