March 31, 1999

The moment that Japanese astronomers have been waiting for has arrived. Twenty years since its conception, Subaru, a large optical infrared telescope constructed by the National Astronomical Observatory of Japan, has finally begun test operations. Its "first light" (first observation) images were presented to the public in January 1999, including those of nearby Saturn and Jupiter, young stars forming within the Orion nebula 1,500 light years away, and the farthest known celestial entity, a quasar 14 billion light years in the distance. The images are among the most beautiful ever captured by a ground-based telescope. Even before its official start of operations, Subaru has stirred the investigative spirit of Japan's--as well as the world's--astronomers.

Long-Awaited Telescope
Blessed with clear skies most of the time and little atmospheric turbulence to blur celestial images, the summit of Mauna Kea on the island of Hawaii is an ideal spot for astronomical observation. More than 10 giant telescopes dot the landscape, all world-class wonders. Among them are the twin Keck Telescopes, the world's largest, and the Gemini North Telescope being built by a multinational project group that includes Britain, Canada, and the United States. Japan's Subaru Telescope stands there as well.

For many years since the 1980s Subaru had been the dream telescope for astronomers in Japan, which until now did not have any large telescopes. Subaru will thus be outfitted with numerous highly sophisticated instruments, with hopes of unraveling the most profound mysteries of the universe.

The greatest feature of this telescope is its primary mirror, which at 8.3 meters (27 feet) across is the world's largest monolithic (having one single, seamless surface) mirror. Subaru's images are not quite as sharp as those of the U.S. Hubble Space Telescope because ground-based observatories inevitably receive atmospheric interference. But thanks to the size of its primary mirror, its light-gathering ability surpasses Hubble's by more than tenfold. In a galaxy cluster some five billion light years away, Subaru captured in two hours images of several faint galaxies that the space telescope could not detect even after seven hours of exposure. Its field of vision, furthermore, is 100 times wider than that of Hubble, allowing it to search out a large number of celestial objects in a short time.

Aiming for a Sharper Image
Many other features are included in the Subaru Telescope to achieve the sharpest image possible with ground-based observation. It took four years to polish and shape the primary mirror, made of special glass that is affected minimally by changes in temperature. The mirror is only 20 centimeters (8 inches) thick; 261 computer-controlled arms support it from the back, automatically correcting errors in its shape caused when gravity makes it sag.

Furthermore, the structure housing Subaru is cylindrical, unlike the semi-spherical enclosures used for most large telescopes. This is to minimize atmospheric turbulence around the telescope, which would degrade the resolution of its images.

Finding Distant Planets in the Infrared
Subaru will mainly be used for observation from the optical to infrared wavelengths. Research using the infrared spectrum in particular is a relatively undeveloped field, and major achievements are expected through infrared observation of faraway planets too dim to be seen as optical images or objects shrouded in opaque gases. There have been several reports in the past of planets being discovered outside the solar system, but these discoveries have all been based on indirect evidence, such as a wobble in a star's movement thought to be caused by a planet's gravitational pull. Subaru will enable direct observation, however, by first blocking the light from the star around which a planet is orbiting, then detecting the planet's light in the infrared range.

Another of Subaru's missions is to probe the far corners of the universe, more than 10 billion light years away. By observing with Subaru the faintest light that reaches Earth from such distances, Japanese astronomers hope to gain new understanding of the origins of the universe and its formation process.

Japan's astronomers expect it will take another year to fine-tune this state-of-the-art telescope before it goes into full operation in the year 2000.

Edited by Japan Echo Inc. based on domestic Japanese news sources. Articles presented here are offered for reference purposes and do not necessarily represent the policy or views of the Japanese Government.

---