COLUMN ONE : It’s All Done With Mirrors : Two new technologies for bigger telescopes are revolutionizing astronomy. The science is on the brink of an extraordinary era.
Roger Angel hardly seems the type to lead a revolution.
The soft-spoken, Oxford-trained astronomer prowls the corridors of the University of Arizona these days in the pullover sweater and corduroy slacks of the quintessential college professor. Part scientist, part inventor and part dreamer, Angel is the point man in the development of technology that has forever changed the world of science.
The 49-year-old professor is the prime mover behind the university’s mirror laboratory, a huge spinning furnace that melts glass and then allows it to cool and harden in the shape of a telescope mirror. But these are not just ordinary mirrors. These are giant mirrors that will peer into the darkest recesses of the universe, making new discoveries and rewriting the course of modern astronomy.
The technology--one of two new ways of building huge mirrors--saves endless months of costly grinding and it is enabling scientists to build telescopes far larger than considered possible just a few years ago. It is very different from another new technique, favored by many European scientists, which involves creation of a very thin mirror that bends and warps to maintain a near-perfect shape despite changing temperatures and the high winds that howl through mountaintop observatories.
The two technologies are competing for the lead role in the old art of telescope design--but no matter which one wins, the world of astronomy stands on the brink of an extraordinary era.
Just a few years ago, funding had all but dried up for new telescopes, and astronomers were watching one proposal after another go on the shelf because of a lack of money. Funding is still tight, but new technology is bringing the cost down, and astronomy is enjoying extraordinary popular support.
“The science is very compelling,” said Wayne Van Citters, program director for astronomical instrumentation development of the National Science Foundation, which is funding several new scopes. “The scientists can make a hell of an exciting case.”
Citters acknowledges that public support has played a role in increasing the funding. “People are interested in astronomy,” he said. “They can understand it.”
Distant celestial objects that appear as no more than pinpoints of light in today’s largest telescopes will show up in detail in the new mega-scopes, opening worlds that no one has ever seen before. The giant ground-based instruments will work in concert with orbiting observatories, including the Hubble Space Telescope scheduled for launch next month. The Space Telescope, for example, will be able to find objects so small that no one has ever seen them before, but it will take the huge mirrors of the new ground-based telescopes to capture enough light to really study the new discoveries.
Progress has come so quickly that the 10-meter Keck Telescope now being built by Caltech and the University of California atop Hawaii’s Mauna Kea may have a very short reign as the world’s largest telescope. The Keck Telescope, which will use 36 individual mirrors in an array that makes them comparable to a single mirror more than 32 feet across, will be completed sometime next year.
But that’s only the beginning.
“The ‘90s will be a true golden age for the construction of large telescopes,” Pat Osmer, deputy director of the National Optical Astronomy Observatories, told a recent symposium here sponsored by the International Society for Optical Engineering. The National Optical Astronomy Observatories, funded by the National Science Foundation, plans to build two 8-meter telescopes, one on Mauna Kea and the other in Chile, “to give full sky coverage” to American astronomers--a goal that scientists could only dream about a few years ago because few thought it would be possible to fabricate such large mirrors.
An 8-meter mirror is so large it would not even fit inside an oversized double garage, and it offers the hope of probing the darkest regions of the universe. That is because the larger the telescope, the more light it can gather. Thus a great instrument can “see” farther and study dimmer objects than lesser scopes.
The twin observatories will be far larger than the 5-meter Hale Telescope on Palomar Mountain in northern San Diego County, which has dominated the world of astronomy for more than half a century. And even larger telescopes are in the advanced planning stages.
Nothing on the drawing boards, however, matches the bold plans of a consortium of European countries that expects to build a complex of four 8-meter telescopes on a mountain peak in the Chilean Andes. The four scopes will be designed to work either separately or together as the equivalent of a single 16-meter telescope. Thus, this giant telescope will have the light-gathering capability of a mirror 52 feet in diameter. That is more than three times the diameter of the Hale Telescope, the largest now operating in the United States.
The countries involved in the European project are Germany, France, Italy, Switzerland, Belgium, Holland, Denmark and Sweden, and funding has already been secured, according to astronomer Jacques M. Beckers of the European Southern Observatories. The project is expected to cost around $200 million, nearly twice the cost of the Keck Telescope.
“That’s a lot of money,” Beckers said in an interview, “but it will be the world’s most powerful telescope.”
The largest optical telescope in the world today is in the Soviet Union, but the 6-meter scope has been disappointing to astronomers, partly because of poor “seeing” conditions, as astronomers refer to atmospheric limitations on telescopes.
American astronomers dreamed in the 1980s of knocking the Soviets from the top of the mountain by building the world’s largest telescope, a complex of four 8-meter scopes in a single mount. The New Technology Telescope, as it was called, was expected to dominate the world of astronomy.
“But the funding climate was really bad,” said Beckers, who was then one of the leaders in the effort to build the giant telescope. “It looked very grim. People decided the project was just too ambitious.”
So Beckers jumped ship and joined up with the Europeans. The U.S. project is dead, but the European “Very Large Telescope” is remarkably similar to the one that American astronomers had dreamed of. It is also quite different.
Unlike the U.S. design, which called for all four of the huge mirrors to be fixed in a single mount, and thus forced to focus on the same target, Europe will provide separate mounts for each of the mirrors. Thus the telescopes can work either together, or separately, or even with a number of other smaller telescopes that will be located around the main complex.
The concept of blending the light from several telescopes into one beam, and thus greatly increasing the size of the scope, was pioneered by American astronomers with the “Multiple Mirror Telescope” in Arizona. That scope took the light from six mirrors and blended it together, thus using six smaller mirrors to work as a single 4.5-meter telescope.
The Multiple Mirror Telescope was “experimental,” according to astronomer Frederic H. Chaffee, director of the facility.
“We wanted to know whether one could make a cluster of telescopes function as a single telescope,” Chaffee said. “It worked extremely well. The astronomer was unaware of the fact that he was using six telescopes instead of one.”
Yet that telescope, which has been operational for only a few years, is already obsolete because of the rapid pace in the development of telescope technology. The six-mirror complex will be replaced by a new 6.5-meter mirror.
The decision to abandon the multiple mirror scope, Chaffee said, came about because “we realized it would not be competitive in an 8-meter world.”
By using the existing dome and support facilities, and replacing the primary mirror with a larger one, the facility will join the front ranks of astronomy at a cost of only about $15.5 million, Chaffee said. A complete new telescope of that size, including a new dome, would have cost at least three times that much, he added.
But putting a 6.5-meter mirror in a 4.5-meter telescope is a little like stuffing your size 9 foot into a size 6 shoe. It is possible, however, because of advances in telescope technology.
The University of Arizona’s spin furnace can create a huge slab of glass in about 24 hours with a surface that is curved enough to focus the light from distant stars very close to the mirror, thus greatly reducing the size of the support structure needed for the telescope.
That not only lowers the cost of a large telescope considerably, it makes it possible to stick a big foot in a small shoe, as Chaffee plans to do with the Multiple Mirror Telescope by the end of 1994.
However, the concept pioneered by the Multiple Mirror Telescope is far from dead, and many telescopes in the years ahead will look quite different from their predecessors.
For example, the University of Arizona, Ohio State University and Italy are joining together to build powerful “binoculars” consisting of two 8-meter telescopes mounted side by side, according to Peter A. Strittmatter, director of Arizona’s Steward Observatory.
The twin mirrors will be equivalent to a single 11.3-meter telescope, so when it goes into full operation in 1996 it should rank as the largest in the world, at least until the Europeans finish their giant in Chile. The scope is expected to begin limited operations with the first mirror in 1994.
The complex is supposed to be built atop Mt. Graham in Arizona, but environmentalists are fighting the project because they believe it will endanger the habitat of a rare squirrel and generally degrade the pristine area.
Chaffee said the “binoculars” will use mirrors cast in the university’s spin-furnace, and that is one reason why the project is expected to be completed at a relatively modest cost of $60 million. The reduced costs of the big mirrors, which Angel expects to bring down even more in the years ahead, is helping to make it possible for more and more universities to have their own major telescopes.
The Carnegie Institution, for example, has joined with Johns Hopkins University and the University of Arizona in plans to build an 8-meter telescope, called Magellan, in Chile. Carnegie’s Alan Dressler said he expects Magellan to cost about $45 million.
By contrast, the high-tech Keck Telescope is expected to cost well over $100 million by the time it is completed in Hawaii. That telescope will use 36 hexagonal mirrors in an array that will be comparable to a 10-meter telescope.
However, many scientists believe the real pacesetter in telescopes is a relatively small, 3.5-meter scope at the European Southern Observatory’s La Silla facility north of Santiago, Chile. The New Technology Telescope began operations last March, and it has already produced images that have startled astronomers.
The telescope uses a system of sensors and computers to bend the mirror so that its reflective surface remains nearly perfect, even when the temperature suddenly changes. That has permitted the telescope “to achieve the natural seeing limits,” meaning it works better than any other telescope in the world, according to Masimo Tarenghi, the project manager.
Sky and Telescope magazine recently called it “a telescope for tomorrow,” and the European project has already strutted its stuff.
During the Tucson meeting, Tarenghi showed an old photo of one area of the sky which included an object that all surveys list as a star because it appears in all previous images as just another point of light. But the image created by the new telescope revealed that it is not a point, but rather a swirl of light. Far from being a single star, it is a galaxy of billions of stars, worlds that no one even knew were there.
The large mirrors built by Angel’s group are in competition with the high-tech “active optics” favored by the Europeans, and no one knows at this point which will win out as the wave of the future. But no one doubts that the world of astronomy will never be the same again.
