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Prague Astronomical Clock

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This is photo of the Prague Astronomical Clock (Pražský orloj). And now it's time for a lesson on how to read the clock, as it's not nearly as complicated as it may seem, I assure you.

Background:
This represents the horizon as seen from earth and is divided into sections - the bright blue bit is day, then (on the right) we have OCCASVS (sunset) and CREPVSCVLVM (twilight); then we have the black section which represents night; and finally we have AVRORA (dawn), and ORTVS (rising).

The Sun:
This has several purposes. By slowly moving up and down its hand over the year (furthest up in summer and furthest down in winter) it gives the time of sunrise and sunset (by crossing the appropriate divisions in the background at different times). It also marks the start and end time of the unequal hours (a system of time measurement in which the day is split into twelve hours starting at sunrise and ending at sunset which of course means the length of each hour changes throughout the year). Finally it shows the sun's position on the zodiac - at the time the picture was taken the sun was in Aries (sun signs are the most commonly known astrological signs, and the ones used in magazine horoscopes).

The Golden Hand:
This is what tells the time - it moves once around the clock each day, and the time can be read from the golden Roman numerals - the twelve at the top represents midday, and the twelve at the bottom represents midnight. As you can see, it's around half-past two in the afternoon when this photo was taken. This hand is also what the sun is attached to, and is what moves it across the sky (the background).

The Moon:
This hand moves once around the dial (anti-clockwise) about once a month, and slowly moves up and down the hand in accordance with the current position and height of the sun (the two hands are connected). It also has one sliver side and one black side, which rotate to tell you the phase of the moon - in the photo, the moon is waning and was full quite recently.

The Zodiac Ring:
This large ring is divided up to show all twelve zodiac symbols in anti-clockwise order, and the sun appears in each one for the same length of time - one month. The little star attached to this ring represents the vernal equinox...though I admit I don't quite know its function yet - it might be something to do with sidereal time.

The Outer Ring:
This ring, marked with the numbers 1 to 24 is old Czech time (also known as Italian Hours) in which the number 24 was always located at sunset. Because of this the ring revolves as the year goes on, with the 24 being further up in the winter, and further down in the summer. The approximate time of sunset can then be read from the Roman numerals - when I was there, it was at around 6:30.

So there you have it - now you can read the Prague Astronomical Clock. Good for you.
Image size
2518x2382px 4.15 MB
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Comments1
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Bleeding-Abyss's avatar
I have always loved astronomy, clocks, astrology, and anything related to the stars. I find astronomical clocks fascinating because it's basically everything I love in one.