Transcript PowerPoint on Astrolabe

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.
11/15/99
Norm Herr (sample file)