Smoothest surface in the world

The most accurate mirror ever made is shortly to begin its journey to an observatory in Hawaii. Our science editor Dr David Whitehouse reports.

Japan's National Astronomical Observatory (NAOJ) has just completed one of the world's largest telescope mirrors, with a diameter of 8.3 metres (27 feet).

It is one of the smoothest surfaces ever fashioned by man. To understand how smooth imagine enlarging the 8.3 m surface to 82 km (51 miles), which is about the size of the big island of Hawaii.

There would be no hills or valleys (on average) taller or deeper than 0.12 mm (0.005"), the thickness of an ordinary sheet of paper!

The mirror will leave the laboratory of Contraves Brashear Systems of Pittsburgh later this month to journey to the summit of the extinct Mauna Kea volcano in Hawaii.

At the summit, the mirror will receive a thin coating of pure aluminium to make it highly reflective and finally be attached to the telescope's mechanical structure.

Tests to evaluate the telescope's performance will follow. Scientists are planning to obtain the first scientifically important images (First Light) at the end of January next year.

The mirror is supported by 261

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