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A mountaintop perch with views of the starry sky

The age of video astronomy begins in the Kiso Mountains

October 1, 2021

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The 105 cm Schmidt telescope at Kiso Observatory. ©Koji Okumura (Forward Stroke, Inc.)

Light is the greatest enemy of astronomical observation. A dark night sky is essential to capturing light from distant objects, which is why the Kiso Observatory was built high in the mountains above the town of Kiso in Nagano Prefecture in 1974.

This observatory far from Tokyo may now play a renewed role in astronomy. A new tool has been introduced there that can capture rapid changes in the universe in video format. This tool is the new camera, dubbed Tomo-e Gozen, which was commissioned at the Kiso Observatory in October 2019.

Tomo-e Gozen is equipped with 84 highly sensitive CMOS sensors developed by Canon. High-speed data acquisition is only possible with CMOS sensors, which enable us to observe moving images at two frames per second. This has overturned the conventional image of astronomical photography, where it was once normal practice to take a still image with a long exposure, heralding the age of video astronomy.

Tomo-e Gozen is mounted on a 105-cm diameter Schmidt telescope at the Kiso Observatory. The Schmidt telescope is distinguished by a large correcting lens attached to the top end of the lens barrel to produce blur-free sharp images over a wide field of view.

There are many telescopes with larger diameters than the Kiso Observatory’s Schmidt telescope, but most of them are optimized for detailed observation of specific areas of the sky. In short, these telescopes act like huge telephoto lenses and their fields of view are limited. The Schmidt telescope, on the other hand, has a wide-angle lens that captures a large area at once. The Kiso Observatory boasts the largest Schmidt telescope in Japan and the fourth largest in the world. Since its completion by Nippon Kogaku Kogyo (now Nikon) in 1974, it has been taking photographs of the sky for more than 45 years. It was not easy to adapt the digital technology to this telescope, which had failed to take advantage of its ultra-wide field of view. It was the development of Tomo-e Gozen that changed that trend.

The Schmidt telescope equipped with Tomo-e Gozen is essentially an ultra-high-definition, ultra-wide-angle giant digital camera. When combined with 84 CMOS sensors, it boasts a super high definition capability of 190 million pixels. Furthermore, each individual sensor covers the field of view of one full moon, making it possible for Tomo-e Gozen to photograph an area equivalent to 84 full moons at once. Discovering unknown astronomical phenomena is now a distinct possibility because video footage can be obtained over a wide field of view. In fact, several new observations have already been made during pilot operations. Tomo-e Gozen discovered a supernova explosion and new celestial bodiesasteroids, and revealed that an astronomical body at the edges of the solar system known as Quaoar has almost no atmosphere.

Tomo-e Gozen’s 84 high-sensitivity CMOS sensors mounted on the Schmidt telescope.

The Kiso Observatory also has a thriving outreach program. In addition to providing access to the general public in the summer and various initiatives for the local community, a three-night, four-day “Galaxy School” is held every spring for about 30 high school students from across Japan. They collect observational data for astronomical objects with the Schmidt telescope and analyze the data using computers, then present their results to the other participants. In the 22 editions of the Galaxy School since its launch in 1998, around 600 students have benefited from this program hosted by the Kiso Observatory. Some graduates of the Galaxy School have gone on to become astronomers or researchers in the natural sciences. The Observatory’s outreach programs have also been key in educating society and fostering scientific literacy. What kind of graduates will it produce from 2020, now Tomo-e Gozen is fully operational and video astronomy will become commonplace?

Interview and text: Masatsugu Kayahara
​Photography: Junichi Kaizuka

Originally published in The School of Science Brochure 2020

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