Making a Star Clock (Astrolabe)

11/15/99 Norm Herr (sample file)

Making a Star Clock (Astrolabe)

11/15/99 Norm Herr (sample file)

Astrolabe

• The astrolabe is a type of ancient astronomical computer which was used to solve problems relating to time and the position of the Sun and stars in the sky.

• A type of astrolabe was also used for navigation until the invention of the sextant in the 18th century.

11/15/99 Norm Herr (sample file)

Method

11/15/99 Norm Herr (sample file)

Method 1. Cut around the outline of both circles.2.  Fix the small circle on top of the larger circle in such a way

that it can spin freely. 3. Find the Plough (or Big Dipper) in the sky: this constellation is

also shown on the face of the clock. 4. Face the North Star as shown on the face of the clock 5. Find the current month around the outside circle of the star

clock. Put your thumb over the current month. Hold your Star Clock so the current month is AT THE TOP.

6. Turn the smaller disc until its stars line up with those in the sky.7. Read the time in the window.

11/15/99 Norm Herr (sample file)

Why does it work?

• The star clock works because the North Star (currently Polaris) is almost directly above the North Pole.

• Polaris appears to stay in a fixed position in the sky while all others rotate around it at a constant rate

• This rotation of other stars and constellations like the Plough can be used to mark regular intervals of time just as we have done with the star clock.