Experts talk about the astronomical clock and the wonder of "Christian van der Klaauw"

In July 2025, Isetan Shinjuku held its annual watch festival, Watch Collectors Week. This year's theme was "Synchronizing Astronomy and Clocks," and the highlight of the event was the Grand Planetarium Eccentric Meteorite, a new model by Christian van der Klaauw, the world's only manufacturer specializing in astronomical watches. In front of this watch, of which only three exist in the world, a closed event was held where experts, including Masamasa Hirota, editor-in-chief of Chronos Japan, spoke about astronomical clocks. This article reports on some of the content of the talk.

Christian van der Klaauw's masterpiece on display at Isetan Shinjuku

　In early July 2025, the annual watch festival "Watch Collectors Week" was held at the Isetan Shinjuku store. This year's theme was "Synchronization of Astronomy and Watches," and a collaborative project called "From Chi to Watches" was held in collaboration with the manga "Chi - About the Movement of the Earth." The event featured a wide range of exhibits and explanatory events on the history of astronomy and watches, attracting many visitors every day.

The special exhibition "From Chi to Watch" is currently being held. "Chi - About the Movement of the Earth" x the world of mechanical watches. An experiential exhibition that traces the connection between space and time.
Dates: July 2nd (Wed) - July 8th (Tue)
Venue: Isetan Shinjuku Main Building 5th Floor The Stage #5#ChiExhibition #WatchCollectorsWeek #ChristianVanderKlaau pic.twitter.com/pv0SVQeJbg

— ~Dear Watch Lover,~ by shellman (@DearWatchLover) July 2, 2025

　One watch that attracted a lot of attention at the venue was the collection of watches by Christiaan van der Klaauw, the world's only manufacturer specializing in astronomical clocks, based in the Netherlands. Among the unique pieces featuring a wide variety of astronomical displays produced by the company, the highlight was the "Grand Planetarium Eccentric Meteorite," a masterpiece released this spring. It features an unprecedented planetarium function that reproduces the movements of all eight planets in the solar system, from Mercury to Neptune, in real time in eccentric orbits. Also on special display was a rare watch, one of three limited edition watches with a meteorite case covering the entire surface, which was being shown in Japan for the first time.

　During the event, a closed talk event was also held for customers. In addition to Hirota Masamasa, editor-in-chief of Chronos Japan, Inoue Takeshi, director of Akashi City Astronomical Science Museum, Mouri Katsuhiro, astronomy section chief at Nagoya City Science Museum, and Pim Korslag, CEO of Christian van der Klaauw, took the stage to share their views on astronomical clocks from their respective perspectives. With a wealth of specialized knowledge, it was truly a luxurious experience that astronomical clock fans will not be able to resist. While I cannot include the entire text here, I would like to share with you the parts that made the biggest impression on me.

Akashi Municipal Astronomical Science Museum Director Tsuyoshi Inoue Theme: "Clocks and Astronomy"

　The first speaker at the talk event was Tsuyoshi Inoue, director of the Akashi Municipal Astronomical Museum in Hyogo Prefecture. Located on the 135th meridian east, which is the basis for Japan Standard Time, the Akashi Municipal Astronomical Museum has hosted numerous exhibitions on the theme of "time and astronomy." In June 2023, a special exhibition showcasing Christian van der Klaauw was held. Inoue himself has long been researching clocks and astronomy, and in 2023 he published a book on the theme of planetariums, "The Machine That Creates the Starry Sky: A 100-Year History of Planetariums" (KADOKAWA). The book also touches on the Giovanni de Dondi astronomical clock, a pioneer of mechanical astronomical clocks.

　Inoue began by talking about the history of planetariums. He said, "The relationship between planetariums and clocks is not widely known, but historically there is a very deep connection." He explained the reason for this by tracing the roots of today's typical planetariums, which use a projector to project the stars onto a round dome. "The idea for the dome originated from the famous Italian Farnese celestial globe (the ancient Roman sculpture, the Farnese Atlas). The projector's mechanism, in turn, originated from the orrery, a device used to reproduce the movement of the planets. Furthermore, the prototype of this can be traced back to the Antikythera Mechanism, an ancient computer created in ancient Greece and discovered about 100 years ago. (This mechanism, which combines gears and other mechanisms to calculate the movement of celestial bodies and the calendar, was discovered about 100 years ago.) Explaining these points, Inoue continued.

"The period from ancient Greece to the Middle Ages and the period of the Scientific Revolution after Copernicus is particularly fascinating in the history of timepieces, and yet much remains unknown. We don't know in detail what happened in the more than 1000 years between the creation of the Antikythera Mechanism and the birth of the mechanical clock. However, technology must have been passed down for sure. The technique of reproducing the movement of celestial bodies using gears and knowledge of astronomy spread from ancient Greece to Rome and then to the Islamic world, where it was developed before being re-imported to Europe during the Renaissance. The astralium (made by Giovanni de Dondi in 1364), which I am currently personally interested in, was a device commonly needed by astronomers of the time, and its construction required an accurate understanding of the celestial bodies. Mechanisms such as these lie at the roots of the astronomical clock."

　Inoue also spoke about the development of Copernican astronomy and the scientific revolution, as well as Galileo Galilei and the Dutchman Christiaan Huygens, two important figures in both horology and astronomy. This year, 2025, marks the 350th anniversary of Huygens' invention of the balance spring. In 1675, he invented the spiral balance spring attached to the balance wheel, an invention that dramatically improved the accuracy of watches.

Mr. Katsuhiro Mori, Astronomy Section Chief, Nagoya City Science Museum Theme: "The Netherlands and Astronomy"

　Next to take the stage was Katsuhiro Mohri, head of the Astronomy Department at the Nagoya City Science Museum. Mohri is a leading expert in Japan on the Eisinga Planetarium. The Eisinga Planetarium is a mechanical model that reproduces the movement of planets in the solar system, completed in 1781 by Dutch amateur astronomer Eise Eisinga, and is the world's oldest surviving mechanical planetarium. A life-size replica has been on display at the Nagoya City Science Museum since 2011, and Mohri has been researching the Eisinga Planetarium since then. During the talk show, Mohri described the Eisinga Planetarium, which uses the power of a pendulum and weight to drive its intricate mechanism, as "truly what could be called an 'Eisinga astronomical clock.'"

　Fate is a bond that connects people. In 2023, when the Eise Eisinger Planetarium was designated a World Heritage Site, Pim Korslag, newly appointed CEO of Christiaan van der Klaauw, visited the Nagoya City Science Museum to see the replica. Impressed by the magnificent appearance of the museum's "world's largest" planetarium dome, Korslag immediately came up with the idea of ​​collaborating with the brand's signature "world's smallest planetarium." The following year, the "CVDK Planetarium Nagoya City Science Museum Model" was completed, and one of the six models was donated to the Nagoya City Science Museum, where it is now on permanent display. (Prior to this, Christiaan van der Klaauw also donated a sample of the "Planetarium Eise Eisinger Limited Edition" to the museum.)

　Mouri also gave a detailed explanation of the meteorite used on the dial of Christian van der Klaauw's latest work, "Grand Planetarium Eccentric Meteorite." He said, "The five meteorite fragments on the dial are nakhlite, a rock (basaltic magma) formed when a volcano on Mars erupted 13 billion years ago. They were ejected from Mars 100 million years ago. A large meteorite probably fell on Mars, breaking free from gravity and gravitational pull and flying into space. They fell to Earth about 10,000 years ago. They were then recovered in the Algerian desert in 2020. This meteorite has an incredible history."

　Meanwhile, there is an interesting story behind the meteorite used for the case and dial, which suggests a connection to the museum.

"The Widmanstätten pattern (lattice pattern) on this meteorite was formed by the slow cooling and solidification of iron and nickel components over an incredibly long period of time, enough to cause the temperature to drop by one degree every tens of thousands of years. It is likely that material was born in the center of a now-extinct star, approximately 46 billion years ago, when the planets in our solar system were born, and then fell to Earth. In order to be used as a watch case, the meteorite must be fairly large and homogeneous. From that perspective, of the many meteorites that have been confirmed on Earth, the meteorites used for the case can be narrowed down to three types. One of these was actually exhibited at the Nagoya City Science Museum in 2000. It is possible that the meteorite used for this watch case is the same one from that time."

CEO Christiaan van der Klaauw and Pim Korslag Theme: "Grand Planetarium Eccentric Meteorite"

　Pim Korslag, the third-generation CEO of Christian van der Klaauw, who visited Japan for the event, explained the new "Grand Planetarium Eccentric Meteorite," a highlight of Watch Collector's Week. He began by explaining the company: "Last year, in 2024, Christian van der Klaauw celebrated its 50th anniversary. Our founder, Christian, who turns 81 this year, established his workshop in 1974 and began producing astronomical table clocks as a "specialist manufacturer of astronomical clocks." Today, our headquarters is located in a beautiful building about a 20-minute drive from Amsterdam Airport in the Netherlands. The machinery used in this workshop has been passed down since the company was founded."

　All pins, screws and levers in Christian van der Klaauw's watches are made in-house.

　Korslag continued, "The movement in the Grand Planetarium Eccentric is the most complex we have ever made," with 365 components and 3338 teeth.

"Planning for this complicated mechanism began in 2022. Christian completes all of the drawings and calculations by hand. The hand-drawn drawings were first converted into 2D and finally into a 3D CAD program. The painting of the planets was also done by hand. The Earth is 1.2 mm in diameter, and when viewed under a microscope you can see that it even includes the oceans and continents. Mercury, the planet closest to the sun, has an orbital period of approximately 88 days, while Neptune, the planet farthest from the sun, takes approximately 164 years. This watch faithfully reproduces the magnificent scale of the universe depicted by the eight planets on the dial."

Masamasa Hirota, Editor-in-Chief of Kronos Japan Theme: "About Christian van der Klaauw"

　The final speaker, our editor-in-chief, Masamasa Hirota, spoke about the "difficulty of manufacturing an astronomical clock." The basic mechanism of an astronomical clock that shows the movement of the planets is based on a basic gear train that displays the hours and minutes, and slows down the rotation speed to match each star. "In theory, it's simple," Hirota prefaced his explanation, saying:

"There are two ways to slow down the speed. One is to make very precise gears. The other is to increase the case size (to increase the number of parts). That's why, until a few decades ago, the only astronomical clocks on the market were basically clocks. Then, from around the 1980s, it became possible to manufacture precise gears, and wristwatch-type astronomical clocks began to flourish. In the end, however, it was difficult. If the gears are made finer and the number of parts is increased, the watch becomes more vulnerable to shocks and is more likely to stop due to poor meshing. In astronomical clock manufacturing, having precise gears is a prerequisite. However, even if you can obtain them, it is extremely difficult to finally complete the watch. That's why astronomical clocks are not made very often."

　Among these, Christian van der Klaauw stands out as a unique artist.
"Van der Klaauw makes precision gears and assembles them reliably. For many years, he has been challenging himself to create as many mechanical astronomical clocks as possible, down to the size of a wristwatch. He is involved in the most cutting-edge aspects of astronomical clocks that can only be made now. The fact that he has managed to create the Grand Planetarium Eccentric (featuring a precision planetary globe) in a case diameter of just 44mm is actually incredible. In other words, it could be said to be the ultimate form of an astronomical clock."

　Christian van der Klaauw continues to condense the laws of the universe into his watches through extremely precise mechanisms. Finally, Editor-in-Chief Hirota asked CEO Korslag, "Why pursue such precision, even at the risk of making the watches difficult to operate?" His answer reflected his determination to faithfully protect the workshop and spirit he inherited from his respected predecessors, a man who was once renowned as a master watchmaker for his numerous developments.

"It's true that the more precision you strive for, the greater the risks. However, what we value as a brand is not only creating beautiful, high-quality products, but also having a solid scientific basis behind them. This sets us apart from other brands. This belief is what we value above all else."