Sonoma County astronomers are putting the finishing touches on a 40-inch mirror, which will be the heart of a new telescope that will peer into the outer edges of the universe.

The telescope will be the largest in Sonoma County, one of only six or seven that large in the state and one of the very few available for public viewing, said Steve Follett, who is building the mirror for the Ferguson Observatory at Sugarloaf State Park.

"There aren't too many of them around," Follett said. "This observatory is dedicated to public observing and visual observing. It is all public astronomy. We are not doing private research."

Follett, a computer programmer, is the optician for the Valley of the Moon Observatory Association, a group of amateur astronomers who own and run the Ferguson Observatory.

With the light-gathering capability of the big mirror, the telescope will be able to bring into focus galaxies that are 2 to 3 billion light years away, in the far reaches of the universe, said George Loyer, association president.

"Once you get a bit more light, you see not only the shapes themselves, but you will see the color," Loyer said. "It won't be as amazing as the Hubble telescope view, but there is something about the ability to put your eye to the eyepiece and see something that you have only seen in photographs. It is a more emotional experience."

The telescope project started in 2003, when association members started collecting pieces.

Follett started grinding the mirror, a giant piece of two-inch thick glass, on a mammoth turntable in his Santa Rosa garage in 2008.

The glass was bought from an amateur telescope-maker in Stockton for $5,000, which is a tenth of what a finished mirror would cost. It had already been ground into a parabolic shape, but then underwent hundreds of hours of grinding on Follett's polishing table, which had been constructed at Caltech in 1912 in Pasadena, using a washing machine motor to drive a gear box and spindle.

Last fall, the mirror was installed in its 12-foot housing and tested at Ferguson Observatory, but the image was unsatisfactory.

The target, Mars, showed up as just a featureless disk.

"With a 40-inch, you should be able to see light and dark markings, polar ice caps," Follett said. "I am not sure whether the moons of Mars are visible, but it should be as big and as bright and as clear as the sky permits."

The mirror now is being polished to a tolerance of 20,000th of an inch, using measurements of a laser-beam machine called an interferometer, also constructed by the association, and computer-aided analysis.

The process could take until the end of this year, after which the mirror will be coated with aluminum, Follett said.

When done, it will join the association's 20-inch telescope and its new solar telescope in public programs, but offer viewers much more than looking at the planets or sun.

Those celestial bodies are the low-hanging fruit, Follett said.

"There are literally tens of thousands of galaxies that will be within the grasp of the scope," Follett said. "Most of the things out there are not very bright, and we wanted the public to see easily, rather than strain or be underwhelmed that it is just a dim fuzzy spot."