|Originally it was Horologium Oscillatorium
but has since been shortened. It was introduced by La Caile in the
1750's. It is one of the fainter constellations, lying forgotten
alongside the end of Eridanus the River near Achernar. Unlike some
of the other items of technology that were placed in the sky Horologium
could be said to have earned it's place in astronomy.
The Dutchman Christiaan Huygens was the
first to make a working pendulum clock in 1656. Galileo had noticed
that a pendulum regulated mechanism would keep good time but was not able
to complete one before his death. For Huygens, well trained in mathematics
and machinery, is was a relatively simple task. His invention was
quickly taken up by other clock makers and by 1671 you could obtain a pendulum
clock accurate enough that it only lost a second or two per day.
Huygens produced a lot of work in his time: he made better telescopes that
enabled him to discover Titan, the largest moon around Saturn, and to divine
the true nature of Saturn's rings (although it took some time for other
astronomers to recognise him for it) and invented the Huygen's eyepiece
for telescopes, a style that is still made today. NASA has honoured
him by naming the probe that will be dropped into Titan's atmosphere when
the Cassini mission reaches Saturn in 2004 after him.
Now that astronomers had good clocks at
their disposal it was no matter to regulate the timing just a little further
so that the clock kept sidereal time, the time of the stars. A sidereal
day was the time it took a star to return to a particular point in the
sky and because of the orbital motion on the earth this is approximately
4 minutes less than a solar day, the time we use for every day schedules.
Astronomers would place the clock in the observatory with telescope they
used and then scan the sky in a north-south strip. When they found
an object of note they read the time off the clock to get the Right Ascension
(celestial longitude) of the object and read the Declination (celestial
latitude) from another fixed circle connected to the telescope mount.
Pendulum clocks are still seen today, but
mainly as pieces of decorative furniture. The advent digital and
atomic clocks have the made the pendulum clock obsolete for astronomical
This article is ©2002
Stargazers Astronomy Shop