‘Microscope on the Sky’ Developed by UC Berkeley Scientist : Truck-Mounted System May Pinpoint Distant Stars
A Nobel Prize-winning physicist with the University of California here has developed a new telescope system that he says will enable astronomers to pinpoint the position of stars far more accurately than ever before and let them watch the birth of stars otherwise hidden by the dust and gas of the Milky Way.
The system, to be unveiled this week, is the brainchild of Charles Townes, 71, who won the Nobel Prize in physics in 1964 for research that led to the development of the laser and maser.
The heart of the system is two infrared telescopes, mounted on trucks so they can be transported anywhere in the world. The telescopes work in concert to study infrared emissions--or heat--of stars hidden from view by galactic dust. By comparing the signals received by the two scopes at different locations, astronomers can come up with a precise location for the stars.
“This is a microscope on the sky,” Townes said recently as he climbed around one of the scopes in a parking lot behind the Lawrence Berkeley Laboratory in the hills above the University of California campus.
Sharp Image Sought
He expects the system to provide the sharpest image yet of objects as far away as two hundred thousand trillion miles.
The images that computers will recreate from the pattern of radiation captured by the telescopes will be the astronomical equivalent of standing in California and watching a hand waving in New York, he said.
One of the most important advantages of the new system lies in the fact that the extremely short wavelength of infrared radiation allows the rays to squeeze past the dust and gas that hide so much of the universe, and that are especially dense during the early, violent stages of star formation.
“We will be able to look at stars much earlier in their lifetime,” he said. “There are no blind spots for this telescope.”
Townes cranked up one of the two telescopes for the first time on March 16. By the end of the year he expects to have both telescopes in operation on Mt. Wilson and plans to keep them there about two years. After that, they will be transported to whatever area of the globe offers the best viewing, and they can be moved wherever necessary to study specific targets.
Mt. Wilson is suitable for the system because the light pollution that compelled the Carnegie Institution to close the famed 100-inch telescope there in 1985 does not hamper infrared observations.
And ironically, it is an ideal site for infrared observations because of the atmospheric conditions that sometimes make life unpleasant in the Los Angeles Basin.
Since most infrared rays are screened out by the Earth’s atmosphere, infrared telescopes are especially sensitive to winds that stir up the air molecules, thus blocking out more of the radiation and distorting the rays that somehow get through. That air turbulence is what causes stars to appear to twinkle.
Inversion Quiets Winds
However, the inversion layer that so frequently blankets the Los Angeles Basin quiets the winds, contributing to the smog in the valleys below but creating an ideal infrared viewing climate on the mountains.
“Mt. Wilson has a very stable atmosphere because of inversion,” Townes said. “It’s the best place in the continental United States for the steadiness of stars. The stability of the atmosphere there is quite real and valuable.”
About 90% of the infrared radiation reaching the Earth’s upper atmosphere is screened out by the atmosphere before it reaches the ground, contributing to a school of thought that the only way to study the universe in the infrared is with orbiting telescopes. Such satellites have been valuable in recent years to astronomers, but Townes concluded that by making the most use of the small amount of infrared radiation reaching the ground he could do far more, partly because he could build telescopes much larger than orbiting scopes, and he could link them together through something called interferometry.
That technique has been pioneered by radio astronomers, who link two radio telescopes together and use the signals received by one to interfere with the other, blending the waves like converging troughs in a rough sea. The difference between the signals helps astronomers measure precisely the radiation they are receiving. That measurement, fed into a computer, can be used to create a picture--the electronic equivalent to the use of visible light to make a photograph.
Far More Exact
But Townes expects his infrared telescope to be far more exact than even the largest radio telescopes, because the preciseness of interferometry depends partly on the wave length of the radiation being studied.
Radio waves are quite long, ranging from a few inches to several miles, and infrared waves are very short.
“We’re at 1/2,500 of an inch,” Townes said.
“We will get up to 100 times more detail” than other telescopes, he said.
That exactness is particularly important when it comes to determing the position of distant stars.
The $3-million project was financed primarily by the Office of Naval Research because it promises to be a valuable resource in pinpointing stellar positions, a crucial element in navigation.
It will be so precise, Townes said, that even if the two telescopes are only 100 feet apart, one will receive emissions from a distant star slightly before the other. That difference will tell astronomers the exact angle between the telescopes and the star, thus pinpointing its position.
Mounted on Truck
Each of the telescopes is mounted on a large truck with a housing that can be opened by sliding sections along rails. The telescopes consist of an 80-inch flat mirror that can be moved by computer to track stars as they make their apparent migration across the sky. The image is reflected onto a 65-inch parabolic mirror that concentrates the image in the focusing area, much the same as any other reflecting telescope.
However, since the primary purpose of the system is to make very precise measurements, the components must be controlled exactly. Even temperature changes in the air between the two mirrors can throw the system off.
“Everything has to be accurate to about 1/25,000 of an inch,” Townes said.
To achieve that level of control, Townes uses something he is generally credited with creating, lasers.
Lasers are used to align the system, and a laser beam of known frequency is used to calibrate the system.
The system is only the most recent jewel added to Townes’ scientific crown. A distinguished physicist, he turned his attention several years ago to astronomy and is credited with several major advances in his adopted field.
Interstellar Search
He was the first to use radiotelescopes in the successful search for complex molecules in interstellar clouds. And he turned to infrared spectroscopy to detect materials in the clouds that could not be picked up by radiotelescopes.
His latest creation is a marriage of both those fields. One area he expects to concentrate on is the center of the Milky Way galaxy.
