What is an Astronomical Clock? All about them

Clocks are a very essential part of our daily life. They help us guide through the different times of the day while giving us a sense of schedule. The importance of clocks can be inferred by the fact that we wouldn’t have functional internet nor the GPS system if it wasn’t for the super-accurate clocks that we have, called “the atomic clocks”. If you want to know more about them, we have an article written on that too, here is a link if you are interested “What are atomic clocks? All about them“. As this article is going to be revolving around Astronomical clocks rather than Atomic clocks. So without further ado, let’s get right into the main topic of this article.

What Are Astronomical Clocks?

An astronomical clock is a type of clock that displays astronomical information to whoever that takes a glance. It tells information like the relative position of the sun, the moon, and sometimes even major planets. The clock uses Zodiacs to represent months. These Zodiacs are present inside the time dial. Also, to project the movement of the earth, the clock usually features the time dial in the center of the clock.

Before mechanical/Astronomical clocks there were other clocks like the candle clock that were used to tell time, if you want to know more about candle clocks “Click Here

Fun Fact:

The very first mechanical clock that was created by I Hsing in 723 A.D was also an astronomical clock

A picture of the prague astronomcial clock to better answer What is an Astronomical Clock? All about them
What is an Astronomical Clock? All about them

The oldest functional astronomical clock is well over 600 years old and is named as the Prague astronomical clock. It has nonetheless stopped working a few times and was repaired to keep the functionality intact. Most of the astronomical clocks out there have a 24- hour analog dial around the edge. And the current time is told by a picture of the sun or a ball at the end of the pointer

There are many variations when it comes to Astronomical clocks. But there are some commonalities that are present in all Astronomical clocks. What are these things that all Astronomical Clocks have in common? Let’s have a look into them

A 24-Hour Analog Dial

Most clocks have the 24-hour Analog dial on the outer edge of their skeleton. And mark the numbers from I to XII then from I to XII again. The current time is indicated by a golden ball or a picture of the sun usually at the end of the pointer. Moreover, another point to note at this point is that it is quite rare for an astronomical clock to have a minute hand

A picture of the 24-hour Analog Dial to better answer "What is an Astronomical Clock?"
What is an Astronomical Clock?

The indicator ( hand ) indicates the altitude of the sun at the moment. The top of the dial indicating South, the two points ( VI & IV  ); indicating east and west. And these two points: XII and IIX, defining the horizon. Moreover, if the numbers are Arabic rather than Roman than the time might be shown in Italian hours. For those, if you who don’t know, in the Italian hour system, 1’O Clock is at the time of the sunset and then the counting continues throughout the night, reaching 24 hours before sunset.

The 12 Zodiac Signs

As we said before, each zodiac sign is used to represent a month. These Zodiac Signs are usually in a concentric circle inside the 24-hour dial which combined forms an ecliptic projection. This ecliptic dial makes a complete revolution in 23 hours and 56 minutes


There is also usually a moon of some sort, that indicates the age of the moon as days pass. A new moon is shown as a 0 and is shown as full, on day 15. And finally, it wanes up to day 29-30.

Some of the most incredible Astronomical clocks

AlJazari’s Castle clock

Aljazari was a Muslim mathematician who is best known for writing a book on mechanical devices in1206 A.D. This was a book that contained within itself the art of constructing over 100 mechanical devices. In essence, it was one of these mechanical devices that was an Astronomical clock he named “the Castle Clock”

A picture of al-jazaris-castle-clock to better answer "What is an Astronomical Clock?"
What is an Astronomical Clock? All about them

The Castle clock was 11 feet tall and was run by water that was injected into it through the main tank. Consequently, this flow of water then prompted a chain of events that lead to the clock telling the time. Moreover, the clock also becomes a mannequin with the help of automated doors and musical robots after hours. Moreover, the clock also includes a display of the zodiac and the solar as well as the lunar orbits.

Wells Cathedral Clock

A picture of Wells Cathedral clock to better answer "What is an Astronomical Clock?"
What is an Astronomical Clock? All about them

This clock is considered to be the second oldest working clock mechanism in Britain that has survived the battle of time in its original form. It’s internal mechanism dated back to 1362. And was updated in the 19th century. This clock now operates in the London Science Museum. The dial of this clock is quite elegant in its look. It represents the geocentric view of the universe with the sun and the moon revolving around a central fixed earth. Which is understandable the point that one time we even considered ourselves to be the center of the universe.

Su Song’s Cosmic Engine

Before the time when there wasn’t a thing like a telescope. People used to track the time of the month and the year just by looking up into the sky with their naked eyes. At this time, it was the Babylonians that became the first to look up above in the sky for Guidance. Whether informs of months or through the direction of stars. And it took very little time from that for Su song to actually build an Astronomical clock on those principles. The clock made astounded everyone at the time.

 A picture of su-sungs-cosmic-engine to better answer " What is an Astronomical Clock? "
What is an Astronomical Clock?

This clock was build in 1092 A.D. and was fully water-powered like the Aljazari’s Castle Clock. Moreover, the original clock was destroyed abruptly in 1126 A.D. but there does exist a beautiful replica of this phenomenal clock. The replica now exists in the National Museum of Natural Sciences, Taichung city, China.

This was some information about what Astronomical clocks are, what their features are like, how they usually function, and some of the best of them. Albeit, if you have any further questions about Astronomical Clocks than feel free to use the comment section below. And lastly, if you want to know why clocks don’t appear in dreams, we have a great article on just that so do give it a click if you are interested “Why don’t clocks appear in dreams? Clocks and dreams!

AK Iqbal

A University of London’ student with a passion for writing. Clocks have always intrigued me and the importance that they have in our lives is way beyond phenomenal. So, on this site, I write everything about clocks, everything from answering any clock-related queries that you might have along with recommending some of my favorite clocks accordingly. Moreover, I will also be conducting some researches on clock related topics and sharing the things that I learn. So stay tuned to ohmyclock for all the fun clocks related content

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