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National Astronomical Observatory of Japan Hawaii Observatory |Subaru Telescope

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History and Outstanding Features

The stars that shine in the night sky are many and varied; some shine bright and clear, others release only the faintest of light, imperceptible to the human eye. It’s always a moving experience to look up at the clear night sky and witness the twinkling of countless stars. Most of this nightly show of celestial objects, conducted deep in the universe, is invisible to our naked eye. Look into a telescope, however, and the show will unfold in an almost magical experience.

Today, the most advanced telescopes allow us to view celestial objects up to 10 billion light years away. The Subaru Telescope, located on the Manua Kea volcano on the island of Hawaii, is the flagship telescope of the National Astronomical Observatory of Japan (NAOJ).

The NAOJ was established in 1997, and the Subaru Telescope saw its first light in 1999. Work that cannot easily be conducted at the peak of the Mauna Kea volcano, high above sea level, is carried out in the foothills of the mountain, in Hilo. Since its establishment, the Hawaii observatory has been the source of many ground-breaking astronomical findings. Much of this success is thanks to the advanced functionality of the Subaru Telescope.

The World’s Largest Monolithic Primary Mirror

Most important to any telescope is the ability to gather large amounts of light. At the Subaru Telescope, this function is performed by the world’s largest monolithic primary mirror, with an effective diameter of 8.2m. In addition its world-leading size, it also has the highest surface quality, with a mean surface error of 12 nanometers, just 1/5000 of the width of a human hair. Or, to put it another way, if we took the mirror were the size of the island of Hawaii, then the surface of the mirror would differ by no more than the width of a single piece of paper. It is this large and smooth mirror that allows the telescope to gather the faintest light from the depths of the universe.

The mirror, although 8.2m in diameter, is just 20cm thick. In order to minimize any distortion, 261 actuators—robotic ‘fingers’—hold the mirror in place. These actuators are computer controlled, and correct the distortion of the mirror by adjusting its position at a rate of once every 0.1 seconds. This pinpoint control means that the Subaru Telescope mirror is kept in alignment to the greatest accuracy anywhere in the world. The number of actuators—at 261—is also the largest of any telescope in the world today.

The Subaru Telescope, at the peak of the Mauna Kea volcano, is part of a network of facilities, linked through a high-speed connection, also including the Hilo Base Facility, and the Mitaka Campus in Tokyo, Japan. Researchers in Japan are able to use this high-speed network to access data as readily as if they were at the observatory themselves, and conduct observations in real-time.