Few issues in science seem like as delicate or precarious as the enormous mirrors on the hearts of contemporary telescopes. These mirrors — doughnuts of glass meters in diameter, weighing tons and costing hundreds of thousands of {dollars} — are polished inside a fraction of a wavelength of seen gentle into the exact concavity required to collect and focus starlight from the opposite finish of the universe.
When not at work, they’re sheltered in lofty domes that defend them from the distortions of humidity, wind and modifications in temperature. However this can not defend them from all of the vicissitudes of nature and humanity, as I used to be reminded on a current go to to the Las Campanas Observatory in Chile.
As my hosts confirmed off certainly one of their prized telescope mirrors — 20 toes of shiny, immaculately curved aluminum-coated glass — I couldn’t assist noticing a small, suspicious smudge. It regarded just like the type of smear you would possibly discover in your windshield within the morning, particularly should you had parked beneath a tree.
“Birds,” one astronomer grumbled when requested what it was.
It occurs on a regular basis, different astronomers say. Michael Bolte, now an emeritus professor on the College of California, Santa Cruz, recalled giving the governor of Wyoming a tour of the Wyoming Infrared Observatory, exterior Laramie, in 1981. “We went up on the service platform and regarded down, and there have been chicken droppings everywhere in the mirror,” he mentioned. “It regarded terrible.”
It’s not solely birds that may deface a mirror. Mike Brotherton, the present director of the Wyoming observatory, posted an image on Fb of frost that had amassed on his mirror whereas the dome was open for commentary. “It’s arduous to maintain a mirror pristine,” he mentioned. “It’s a stability between opening to take knowledge and defending the mirror.”
Fowl residue has a particular place in astrophysical lore. Within the early Sixties, the radio astronomers Arno Penzias and Robert Wilson, each then at Bell Labs, had been making an attempt to calibrate an outdated horn antenna to review galaxies. In an effort to eliminate a persistent background hum, they shoveled huge quantities of pigeon guano out of their telescope, solely to finally be taught that the hum was cosmic: It was the hissing stays of radiation from the Large Bang, and it firmly settled the query of whether or not the universe had a definite starting.
Fortunately, such biodegradable insults to the mirrors are short-term and don’t block a lot gentle. Observatories periodically wash their mirrors, strip off the outdated aluminum coatings and apply a recent layer, which includes eradicating the mirror from the telescope.
That may be a ticklish operation. Final fall, the 8-meter-diameter major mirror of the Gemini North telescope, on Mauna Kea in Hawaii, was nicked on its periphery whereas being moved for cleansing and recoating. The harm was to not the a part of the mirror that collects gentle, however the telescope’s managers opted to restore it anyway. On March 31, Jen Lotz, the observatory director, reported that the repairs had been full and that the telescope, she hoped, can be again in operation someday in Could.
Some issues are much less simple to repair. On Feb. 5, 1970, a brand new worker on the McDonald Observatory in West Texas took a gun to work and opened fireplace, first at his boss after which a number of instances point-blank on the major mirror of the observatory’s new 2.7-meter reflecting telescope. Then he went at it with a hammer.
Preliminary stories indicated that the mirror had been destroyed; when the sheriff had arrived, he had famous that it had a giant gap in it. In reality the mirror, of a typical sort referred to as Cassegrain, was designed and constructed with central holes to allow gentle to move by way of to devices behind it.
No one was harm in the course of the assault. And except for seven small bullet holes, which affected solely about 1 % of the mirror’s floor space, the telescope was nearly unscathed.
“The telescope resumed its observing program the next evening,” the observatory’s director, Harlan Smith of the College of Texas, reported to the Worldwide Astronomical Union quickly after, “producing a few of the greatest pictures (of quasar fields) up to now obtained with this instrument in its first 12 months of use.”
Which is to say, telescope glass is harder than you assume. After I first visited the 200-inch Hale Telescope on Palomar Mountain in California — a ceremony of passage for a younger science author — I used to be startled to find, wanting down the barrel of what was then the world’s largest and most well-known telescope, a dinner-plate-size gash left by a device {that a} employee had dropped years earlier.
Dr. Bolte described a detailed name on the Canada-France-Hawaii Telescope on Mauna Kea. He and a colleague had been up within the dome, engaged on a digital camera within the telescope, after they seen that the covers that usually protected the mirror had been open. They managed to radio all the way down to the ground and get the covers closed.
“We did no matter we had been going to do, and had been on the brink of come down,” Dr. Bolte wrote in a Fb dialog. “You counted all of the instruments you took to the prime focus cage and made positive the depend on the best way up matched the depend on the best way down. Simply as I used to be saying to Bob, ‘I believe we’re one device brief,’ a giant crescent wrench fell out of the cage and made an unimaginable racket, smacking the mirror cowl.”
Essentially the most well-known instance of what can go fallacious with a mirror occurred in 1990, when the Hubble Area Telescope was launched with a misshapen mirror that would not focus.
Astronauts had been capable of repair it, and Hubble continues to be going robust. However the episode led NASA to be additional cautious with Hubble’s successor, the James Webb Area Telescope, scheduling in depth assessments that vastly elevated the telescope’s value and development time.
The Webb was launched spectacularly and efficiently on Dec. 25, 2021, however area is a taking pictures gallery, too. The telescope had barely arrange store when it was pelted by a larger-than-expected micrometeorite, which left a tiny crater in one of many telescope’s mirror segments. NASA has since modified its protocols to reduce the period of time that the telescope is aimed into meteor streams.
And so it goes. The cosmos has a means of guarding its secrets and techniques.