The Prague Astronomical Clock is a unique
medieval monument. It was built during
the last breaths of the cultural boom in the
Bohemian lands that began under the reign of
Charles IV, Bohemian king and Holy Roman
Emperor, who transformed Prague into a
European centre of learning, culture and
power. The Old Town Astronomical Clock
was built as one of the last medieval archaic
astronomical clocks. These served a different
purpose and were of a different character
than the modern astronomical clocks that
emerged in Europe with the onset of the Renaissance. Its main dials – astrolabes – were
not designed to work like accurate astronomical instruments, but were to be used above all
for astrological purposes. Their design is also
fundamentally opposite to the construction of
astronomical astrolabes.
Unlike most astronomical clocks of the time,
which were made particularly for the interior
of churches, the Prague Astronomical Clock
was built in between the buttresses of the
Old Town Hall tower with great sensitivity. It
faced the outer area of the square in order to
become a part of life in the centre of Prague.
Prague is often called the “heart of Europe”,
as with some exaggeration it can be said that
the astronomical clock is located in the very
centre of Europe.
The Old Town Astronomical Clock is a complicated and multilayered work. The richly
sculptured ornamentation and painted pictorial calendar plate enhance the central motif
of the astronomical clock which is its top dial
– astrolabe. The astrolabe of the medieval
clock is a rotating image of the heavens – the
heavens showing the movement of the Sun,
Moon and stars, as well as the heavens that
are the seat of the God. To the medieval man,
the astronomical clock seemed like a true
miracle. He admired the fact that its creator
had managed not only to understand the
movement of the Sun and Moon across the
sky, but also to imitate it. Everyone could read
the details from its astrolabe – the actual
time, day in the year or how favourable the
constellation of the heavens with the stars,
Sun and Moon is in the life of the individual.
The astronomical clock also indicates the
astrological signs. Astrology and the faith
that earthly things were ruled by the heavens
were very important and commonplace for
life at the time. It was not only used to predict
the future or determine the right moments
for making binding decisions, but also for
correctly timing the performance of medical
The movement
of the celestial bodies
The plate of the astrolabe represents a view
of the southern sky. The bottom is marked
by a golden line of the arch of the horizon
and above it is the blue sky showing the
movement of the Sun, Moon and stars from
left to right, just as in nature. The stars are
represented as constellations marked out in
an excentric circle.
Just as the Sun moves high on the horizon
in late spring and early summer, it orbits the
astrolabe in the same big arch from left to
right along its circumference. The opposite is
the case in winter – the path of the Sun in the
sky and on the astrolabe plate is very low.
The starry sky is depicted only in part – it
shows the constellations of the zodiac
through which the Sun and Moon gradually
move throughout the year. The Sun travels
across the entire circumference of the zodiac
just as it does across the sky in one year, the
Moon in just under 27.5 days. The Sun and
Moon also move very slowly along the zodiacal ring anti-clockwise, then together with the
Sun and Moon, the zodiac rotates along the
astrolabe every day by one clockwise rotation.



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