Based on interviews with Mitsufumi Nishimura, President, and Takayuki Seki, General Manager, Nishimura Co., Ltd., a manufacturer of astronomical telescopes and domes
Telescopes are most often used for astronomical observation. Findings from his star watching convinced Galileo Galilei of the Copernican theory. In Japan, Tokugawa Yoshimune, the eighth shogun of the Edo shogunate of Japan, is said to have enjoyed star watching. Since the ancient times, telescopes have also been used for communication. They have recently found use in laser-based optical communication with artificial satellites. The close integration of lenses, mirrors, mount, dome, and control software ensures high observation accuracy. Japan-based Nishimura Co., Ltd. installed a telescope in an observatory that is located higher than any other observatory in the world. Another Japanese company, an electrical appliance manufacturer, built the world’s largest telescope. Japanese technologies are opening up a bright future for telescopes.
Premodern Uses of Telescopes: Star Watching and Communication
Throughout history, telescopes have been used for two purposes: star watching and communication. In 1608, a Dutch optician named Hans Lippershey found that looking at distant objects through two lenses makes them appear closer. In the following year (1609) , Galileo Galilei invented a three-power telescope, directing its outer end to outer space. Called the Galilean telescope, the primitive refractor employed in those days had a convex lens as the objective lens and a concave lens as the ocular or the eye piece. The Italian astronomer used such a telescope to observe craters on the moon. Studying how Saturn had rings and how Jupiter’s four satellites moved around the planet, he thought that the solar system was governed by the same principles as those smaller systems, which triggered his conversion from the Ptolemaic geocentric theory to the Copernican model. Scientists say that these observations through initial telescopes led Galilei to advocate heliocentrism. Japanese tradition has it that Kunitomo Ikkansai, a famous gun manufacturer in the late Edo period, embarked on building a telescope in 1792, later completing a reflecting telescope of the Gregorian type, featuring a concave primary mirror and an ellipsoidal concave secondary mirror. Tokugawa Yoshimune (1684–1751) , the eighth shogun of the Edo shogunate, is said to have built an observatory in the Edo Castle and observed objects in person day and night. Some of the “Yoshimune telescopes” believed to have been used on those occasions have been passed down until today.
Telescopes’ benefit of making distant objects look closer has also been used for communication purposes. Here, beacons were in use from ancient times until the relatively recent past. This method of setting up a fire at a prominent position so as to be seen from distant locations was used in the military, for example as a warning of an enemy attack. It can transfer information faster and over a longer distance than physical transport by humans or horses. However, it is easily affected by weather and can only convey a small amount of information corresponding to whether or not smoke is emitted. Toward the end of the 18th century, Europe saw the invention of the semaphore line, a communication system that used signaling mechanisms showing character codes, which were read from distant locations—using telescopes. “Hatafuri” or flag waving, a communication system featuring the use of telescopes, was used in Japan from the Edo period to early in the Taisho period (1912–26) .
Starting with Foreign-Made Products, Japan Has Developed the Ability to Make High-Precision Telescopes
Japanese telescope making, which has made big strides since World War II, laid its groundwork before and during the war. In the Meiji period (1868–1912) , the majority of telescopes and binoculars used in this country came from Germany. The military employed foreign-made products during the Russo-Japanese War (1904–05) . According to historians, the binocular used by Admiral Heihachiro Togo (1848–1934) during the war was made by Carl Zeiss AG. Fujii Lens Seizo-sho (Fujii Optical Works, currently Nikon Corporation) was the first binocular manufacturer in Japan, producing and distributing its first model in 1911, which was adopted by the Imperial Navy.
In 1926, Nishimura Co., Ltd. built the first Japanese reflecting telescope and delivered it to Kyoto University. In 1929 the company made and delivered the first Japanese 15-cm refracting telescope. These milestones were followed in 1932 by the building of a telescope for detecting the Einstein effect, which was also delivered to Kyoto University. Nishimura continued to refine its technology by making deliveries to the Tokyo Astronomical Observatory (currently the National Astronomical Observatory of Japan) and manufacturing reflecting telecamera before the end of World War II.
Customer needs to see darker stars are more difficult to fulfill in telescope making. Making dark stars visible requires extending the lens and/or mirror diameters to pick up more light. Resolution is another requirement. Suppose you try to find a planet going around a star through an astronomical telescope. Higher resolution means that your telescope can show the two objects not as being bonded together, but as being separate. This requires not only high accuracy from the lens and/or mirror, but also a measuring technique to see if they have ideal spherical and aspherical surfaces. Also indispensable is a technology for putting together such high-precision components. The slightest error in assembly would be a fatal mistake.
Telescope structure remains much the same since the first telescope was invented. Accuracy has been improved dramatically, however. And that is exactly where Nishimura is strongest. As President Nishimura puts it: “Before the war, our previous President could put together telescopes to such precision as to be considered irreproducible forever.” Not to mention the precision of individual components, the company also excels in making adjustments while putting them together. Many astronomical telescopes are one-off tailored products, i.e., limited to only one worldwide. Nishimura’s know-how to assemble them at their locations of installation forms the core of the company’s unique technology.
Evolution from Equatorial to Altazimuth Mounts, Facilitated by Japanese Control and Manufacturing Technology
Installing a 6.5 m Telescope at the World’s Highest Observatory, at an Altitude of 5,640 m
TAO, the world’s highest astronomical observatory at an altitude of 5,640 m, is a prime embodiment of Nishimura's technology. Located in the South American country of Chile, the facility was operated by Tokyo University to elucidate the secrets of the births of galaxies and planets by infrared observation. Equipped with a one-meter telescope and a dome housing the telescope, TAO was listed in the Guinness World Records in 2011, as the world’s highest astronomical observatory. The new TAO telescope now being developed has an aperture of 6.5 m. Nishimura is responsible for the entire package including a telescope dome.
The world’s largest telescope is the 8.2 m infrared telescope located at an altitude of 4,200 m on the Island of Hawaii. Once completed, the new TAO telescope will be the second largest.
Astronomical observation from the ground suffers from a reduction in sensitivity caused as light from the target object is absorbed and scattered by the Earth’s atmosphere. Building an observatory at a high altitude where the air over is thinner and has lower levels of turbulence allows astronomers to observe objects with high sensitivity and precision. With an increase in altitude, barometric pressure drops; at 5,000 m, it is almost half as high as it is near the ground. Airstreams pose the most difficult challenge. At an altitude of 5,640 m, they seriously affect the quality of observed data. Accordingly, the new TAO telescope is required to provide the world’s highest levels of observation performance. To fulfill the requirements, the geometry of the structures needs to be optimized in consideration of airstreams inside and outside the telescope dome. During observations, it is also necessary to control the airflows within the dome. The project for the new TAO telescope will be completed before the end of March 2018.
Optical Communication Using Lasers and Satellites
Opening Up a New Dimension in Telescope Engineering
In recent years, the Japanese telescope maker has been working on an optical communication system that uses telescopes. Being developed at the request of the National Institute of Information and Communications Technology (NICT) , the system comprises optical communication laser oscillators installed on small satellites and a ground unit to generate a laser beam. The aim is to leverage lasers’ ability to travel along highly straight paths to enable communication between outer space and the ground. Small low-orbit satellites are unlikely to be seen from the ground unless they emit their own light. However, ones that emit near infrared rays are likely to allow ground telescopes to observe their positions and determine their orbits.
While this communication system follows the same basic principles as astronomical telescopes, the difference is that the man-made target moves much faster. This makes it necessary to introduce a technology that enables the telescope to follow it. “Angle errors are only below 10 arcseconds,” says General Manager Seki. (1 arcsecond corresponds to 1/3600 degrees. 10 arcseconds equal 0.0028 degrees) .
Under the project, Nishimura takes care of not only the telescope, mount, and dome, but also software programs for tracking stars and artificial satellites. The company’s original observation software stores data on various celestial bodies. As soon as you set the current time and date, it can therefore show the direction in which a certain body can be observed. Functions for compensating for polar axis setting errors, machine errors caused by the telescope, and atmospheric refractions ensure precise object tracking. All these elements are integrated closely and controlled strictly to achieve high overall precision.
Nishimura’s long-standing passion for precision, which is reminiscent of traditional craftsmanship, also abounds in state-of-the-art laser-based communication technology.
German Equatorial Mount
The German equatorial mount configuration represents the majority of Japanese-made equatorial mounts. It requires a counterweight for balance with the weight of the telescope tube installed on it.
Tokyo University TAO Project
The miniTAO telescope is installed at an altitude of 5,640 m in Chile. Featuring a one-meter aperture and a near infrared camera, it was the first ground telescope in history to observe the center of the Milky Way Galaxy. In addition, its intermediate infrared camera also made it the world’s first ground telescope to detect light rays with a wavelength of 38 µm.
Open Fork Mount
The open fork mount has two arms to support the astronomical telescope. The primary advantage is the lack of a balance weight.
In installing the miniTAO telescope, meticulous tests were conducted in advance to minimize work in the punishing environment at the summit. Elaborate plans were developed to make the team all set for transport to and assembly at the mountain peak. At the summit, temperatures were 0°C during the day and drop to −10°C during the night. The operators worked wearing oxygen masks to prevent altitude sickness. The punishing project involved a two and a half hour drive every day, from the base camp at an altitude of 2,600 m to the observatory site 3,000 m above. The installation work was completed in 2009.
Altazimuth Mount
An instrument used to measure angles, the altazimuth mount features two rotational axes, vertical and horizontal, for supporting the telescope. These axes correspond to longitude and latitude. Fitted with a level, it is used for measuring the positions of celestial bodies and other purposes. It can be combined with a larger telescope since it is better balanced and resistant to higher loads than the equatorial mount. Recent advances in control technologies based on motors and computers have put this type of mount in the mainstream of telescope mounts. The Araki Telescope (see below) and TAO Telescope also feature altazimuth mounts.
Araki Telescope of the Koyama Astronomical Observatory, Kyoto Sangyo University
The Araki Telescope was built in the campus of Kyoto Sangyo University in 2010. The name was given after the university founder Toshima Araki, an astrophysicist and astronomer. At the time of completion, the reflecting telescope with an aperture of 1.3 meters was the largest astronomical telescope that was available at a private university in Japan.
Astronomical Telescope Mount from Early In the Showa Period
Early in the Showa period (1926-1989) , the equatorial mount featured an automatic clock drive using clock work with weights and pendulums. With the spread of electric motors in later years, the mechanical clock drive was replaced by electronically controlled design.