The astrolabe principle of Prague astronomical clock

Prague astronomical clock consists of three main parts: astronomical dial, Jesus and the twelve believers, and calendar clock plate. Astronomical clock plate, representing the position of the sun and the moon in the sky, can display all kinds of astronomical details; "Walking Apostle", a clockwork device can display apostles and other moving statues every hour; A calendar disk consisting of commemorative medals representing months.

Astronomical dial is a mechanical astrolabe. This device was used because people attached great importance to astronomy in the Middle Ages. This astronomical clock is a simple planetarium that shows the initial state of the universe. The background of "Astronomical Dial" shows the eternity of the earth and the sky, and it revolves around the moving elements of four lines, namely, the disk device in the zodiac, the rotating disk device outside and the sun and moon device.

The background of the astronomical clock shows a partial view of the earth and the sky. The blue circle in the middle represents the earth, the blue in the upper part represents the sky above the horizon, and the red and black areas represent the sky below the horizon. During the day, the solar device is on the blue background; Above the dark night; At dawn or dusk, the mechanical sun is active in the red part.

The blue ring on the dial marks the time scale with golden Roman numerals, which divides 24 hours a day into Prague time. The golden curve on the clock plate divides blue into 12 parts, marking every time period from sunrise to sunset, and every day of the year, long or short.

Inside the ring line outside black, there is a movable dial to indicate the zodiac, which marks the position of the ecliptic sun. The pointer in this place turns counterclockwise. In other words, if the sun is in Aries now, the pointer will turn counterclockwise to Taurus. This displacement device of the zodiac is derived from the three-dimensional projection of the north pole of the plan of the zodiac, and is a common manufacturing technology in astronomical clocks. The golden Nomogram number with black background on the outer surface of the clock is a calculation chart with three or more scales of mathematical variable values, which is often used as a quick calculation method in the scientific and technological circles. These numbers mark the old Czech time (or Italian time), and there are 24 ways to mark the sunset time, ranging from 16:00 in winter to 20: 16 in summer. This disk moves back and forth within a year, which is consistent with the sunset time.

During the year, the golden sun device runs on the annular ecliptic circle, indicating the direction of the ecliptic. This solar energy device belongs to the accessory device of the pointer, and together with the gold pointer, it indicates different times in three ways: Prague time, old Czech time and other places. In addition, the distance the sun moves in the center of the dial is the time between sunrise and sunset.

The lunar device running on the ecliptic is similar in function to the solar device. Although it rotates faster, this semi-silver sphere also marks the phase of the moon. Little Venus symbolizes the position of the vernal equinox.

These moving mechanical parts on the astronomical clock disk make it difficult for people to understand time. A simpler way is to apply computer technology to the astronomical clock, so on this clock, every moment of the year is composed of cartoons and spreadsheets, and the time in every part of the world can be explained by mathematics.