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Few issues in science look like as delicate or precarious as the large mirrors on the hearts of recent telescopes. These mirrors — doughnuts of glass meters in diameter, weighing tons and costing thousands and thousands of {dollars} — are polished inside a fraction of a wavelength of seen gentle into the exact concavity required to assemble 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 adjustments in temperature. However this can’t protect 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 one among 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 may discover in your windshield within the morning, particularly when you had parked underneath 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, outdoors Laramie, in 1981. “We went up on the service platform and regarded down, and there have been hen droppings all around 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 gathered on his mirror whereas the dome was open for remark. “It’s laborious to maintain a mirror pristine,” he mentioned. “It’s a steadiness between opening to take knowledge and defending the mirror.”
Hen 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 previous 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 Huge 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 momentary and don’t block a lot gentle. Observatories periodically wash their mirrors, strip off the previous aluminum coatings and apply a contemporary layer, which entails removing 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, would be back 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 occasions 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 studies indicated that the mirror had been destroyed; when the sheriff had arrived, he had famous that it had a giant gap in it. The truth is the mirror, of a typical sort known as Cassegrain, was designed and constructed with central holes to allow gentle to go by to devices behind it.
No person was harm in the course of the assault. And other than seven small bullet holes, which affected solely about 1 p.c 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 International Astronomical Union quickly after, “producing among the greatest pictures (of quasar fields) thus far obtained with this instrument in its first yr of use.”
Which is to say, telescope glass is more durable than you suppose. Once 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 instrument {that a} employee had dropped years earlier.
Dr. Bolte described an in depth name on the Canada-France-Hawaii Telescope on Mauna Kea. He and a colleague had been up within the dome, engaged on a digicam within the telescope, after they observed that the covers that usually protected the mirror had been open. They managed to radio right down to the ground and get the covers closed.
“We did no matter we had been going to do, and had been on the point 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 rely on the best way up matched the rely on the best way down. Simply as I used to be saying to Bob, ‘I feel we’re one instrument quick,’ a giant crescent wrench fell out of the cage and made an unimaginable racket, smacking the mirror cowl.”
Probably the most well-known instance of what can go mistaken with a mirror occurred in 1990, when the Hubble House Telescope was launched with a misshapen mirror that might not focus.
Astronauts had been capable of repair it, and Hubble continues to be going robust. However the episode led NASA to be further cautious with Hubble’s successor, the James Webb House Telescope, scheduling intensive checks that vastly elevated the telescope’s value and building time.
The Webb was launched spectacularly and efficiently on Dec. 25, 2021, however house 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 attenuate 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.
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