Resurfacing the 100-inch Telescope, Aug. 10, 2001
SOCORRO, N.M., August 9, 2001 -- Ever since 1997, New Mexico Tech professor of electrical engineering Scott Teare has spent the better part of his summers in the mountains near Pasadena, Calif., working on the 100-inch Hooker telescope at the Mount Wilson Observatory.
Just like many of the scientists who work on this telescope, Teare has an astronomy research program that uses the telescope, but unlike the hundreds of astronomers who over the years have recorded images through the 84-year-old telescope, Teare also gets the rare opportunity to actually touch -- and, in fact, climb onto -- the large optics of the telescope.
Normally it is not a good thing to be touching the optics; however, Teare also is an optician for the telescope and takes on the responsibility of recoating the 100-inch diameter primary and auxiliary mirrors of the telescope.
In what has become a yearly "face lift" for the aging Hooker telescope, its primary mirror, a 9,000-pound, 13-inch-thick piece of glass is first hoisted down and then its old reflective coating is removed in a series of washes.
The processes involved in cleaning and preparing the huge mirror's surface and applying a new aluminum coating are not complex; nevertheless, there are a number of critical details to coordinate, exotic equipment to operate, and a few "tricks of the trade" to be added in order to obtain the high reflectivity that this old, yet still useful, scientific instrument requires.
"It's a lot of work," Teare says, "at least 100 hours worth just in the optical work after you tally everything up."
But it's rewarding work, Teare adds, especially given the historical context of the Hooker telescope, which among other things was the very same telescope famed astronomer Edwin Hubble used to measure distances and velocities of galaxies, leading to the expanding Universe, or "Big Bang," theory.
The Hooker telescope, completed in 1917, was up until 1948 the world's largest telescope and played major roles in some of the most important advances made in the history of astronomy.
The telescope's 100-inch mirror that Teare works on each summer was originally cast in St. Gobain, France in 1905 and was manufactured from a green glass similar to the type used to make wine bottles.
In 1935, the 60-inch and 100-inch telescope mirrors becamethe first large astronomical telescope mirrors to be aluminized; prior to this, they had to silvered and burnished every few months to maintain its reflectivity. . . . Aluminum coatings can last much longer.
And, the 100-inch mirror still remains the largest solid plate-glass mirror ever made.
"Another perk of working on the 100-inch mirror is that I get to see things few people have ever seen," Teare relates. "For instance, very few people ever get to see the intricate patterns of bubbles that are spread out throughout that big piece of glass. Normally, they are hidden from view by the reflective coating. So, unless you were at the observatory on the one day a year that we are preparing it for the recoating process, you missed it!"
The final step in preparing the glass surface is a scrubbing with a slurry of calcium carbonate, and then the mirror is ready for the evaporative transfer of a new coat of aluminum onto its surface--a process which takes place in the observatory's 108- inch vacuum chamber, essentially a very large steel bell jar which is the same one used to coat the mirrors back in 1935.
The new reflective coating is then tested to ensure it meets set standards, and, after it passes inspection, the 100-inch mirror is then hoisted about 50 feet straight up, to be placed back inside the Hooker telescope's frame.
(Photo by Gale Gant)
"At that point, you just hope that it doesn't fall," Teare says. "It is a wonderful piece of history and an irreplaceable part of a scientific instrument, so we take a lot of precautions and are very careful whenever we are moving it."
Teare's main research involves working with University of Illinois astronomy professor Laird Thompson on a National Science Foundation-sponsored project that is retrofitting the Hooker
telescope with laser-guided star adaptive optics which compensate and correct for optical disturbances caused by atmospheric turbulence.
"Such instruments allow astronomers to do cutting-edge research on existing astronomical telescopes," Teare says, "and will be a necessity on the 30 to 100 meter telescopes that are being planned, in order to take advantage of their available resolution."
As a research physicist at New Mexico Tech, Teare is developing instrumentation and adaptive optics systems for the university's soon-to-be-constructed Magdalena Ridge Observatory,
a state-of-the-art optical observatory that will produce extremely detailed images of the far reaches of the Universe.
In his dual role as a Tech electrical engineering professor, Teare says he will no doubt incorporate some of his summer work experiences at the Mount Wilson Observatory into the new class he has developed in optics and devices, which he is teaching this fall semester at the state-supported research university.