The Physics of Telescope Mirrors

telescopes

In A Hitchhiker’s Guide to the Galaxy, Arthur Dent is confronted by the prospect of the Earth being destroyed to make way for a hyperspace bypass. In countless movies like Star Wars, the universe is depicted as a crowded arena swarming with irate creatures, many of which somehow possess two eyes, two ears, two arms, two legs and a penchant for motor sports.

What’s the truth of it? Well, the answer may indeed be out there; just don’t expect to find it by asking a Hollywood screenwriter. To discover the real truth, you’d either need to talk to a working astronomer, or get yourself a pair of very powerful binoculars. Not the kind you can buy at a shopping mall, mind you, but rather one with lenses 28 feet wide.

Believe it or not, such a binocular actually exists. Called the Large Binocular Telescope (LBT), this $120 million, 500-metric-ton instrument is now atop Mount Graham, east of Tucson. One of the most powerful telescope in the world, the device, using two giant 8.4-meter mirrors working in tandem, is able to peer deeper into the past, and with better clarity, than the Hubble Space Telescope.

Project director Dr. Richard Green said viewing is limited “primarily to those astronomers in the partner institutions that funded the project.” So unless you’re a qualified scientist from the University of Arizona or one of its partners, you can’t use the telescope.

Even for astronomers, finding time on a major telescope can be tough. As Dr. Green put it, “The current demand so exceeds availability that only one project in six or eight actually wins time competitively.”

Different research projects also demand different types of telescopes. “Many telescopes are specialized to record celestial radiation in different ways,” said Dr. Green. This includes not just visible light, but infrared and ultraviolet radiation, plus X-rays, gamma rays and simple radio waves. “Then you have the Large Synoptic Survey Telescope (LSST), also being designed in Tucson, but with a much wider field of view than the LBT so that it can capture the night-to-night changes in faint objects to find moving asteroids and distant exploding supernovae. To continue the pace of discovery, we simply need more telescopes, like biologists need more microscopes.”

And in another nod to Southern Arizona, when institutions need the mirrors used in telescopes like the LBT, the LSST or the upcoming Giant Magellan Telescope, they come to Tucson, on campus at the UA’s Steward Observatory Mirror Lab–a state-of-the-art facility that casts the massive slabs of glass destined to answer some of science’s ultimate questions.

Here in this impressive room, behind the university’s Flandrau Science Center, a huge furnace heats 20 tons of glass, gently spinning it into a parabolic shape at 2,130 degrees Fahrenheit, before cooling and polishing it to an accuracy that’s about 3,000 times thinner than a human hair. Finally, a coating of reflective aluminum is applied, and the lighter-weight mirror or mirrors are then transported to the telescope site.

Arizona is a prime place for telescopes, as are spots in Chile, Hawaii and the Canary Islands, because of four needed attributes, according to Dr. Green: clear skies, dark skies, naturally sharp celestial imaging and low water vapor.

“Southern Arizona has an average of about 75 percent clear hours over the course of a year, and Mount Graham is distant enough from Tucson and Phoenix that the growing light pollution from those metro areas has less impact,” Green said. “All the high peaks in Southern Arizona actually deliver sharp images when the weather is stable, but the high altitude of Mount Graham gives especially low water vapor, of particular value for infrared observations, where water in the atmosphere can absorb celestial radiation.”

The three telescopes now atop Mount Graham–the LBT, the Heinrich Hertz Submillimeter Telescope and the Vatican Observatory Telescope–represent the completion of only the first phase of development. More scopes will be coming, Green said. Indeed, the initial vision called for some seven major telescopes on the site, but the UA will need to formulate an approach with the U.S. Forest Service for the next phase, with environmental concerns a factor.

That’s not to say the Kitt Peak National Observatory has been left behind.

“As a mature facility with moderate aperture telescopes, Kitt Peak observatories are assuming a new and complementary role in astronomy,” Green said. “Their two largest telescopes have mirrors of about 4 meters, with very wide fields of view, and are used more for surveying large areas of the sky for rare objects that can then be followed up with the truly giant telescopes like LBT. Kitt Peak also hosts a number of smaller telescopes run by university consortia that support the long-term projects of their faculty and students.”

Indeed, many astronomers at the UA benefit from Kitt Peak data now, and will from LBT data, too. Like Xiaohui Fan, who holds the record for discovering the most distant quasars, and is ready to start his next survey with LBT. Or Phil Hinz, who is working with NASA support to achieve super-Hubble resolution for detection of extra-solar planets. Green himself has been studying quasars and black holes since his own graduate-student days, when he was a member of the science team that built the Hubble Space Telescope instrument that surveyed nearby giant galaxies, and verified a black hole at the center of every one of them.

Meanwhile, excitement over the LBT’s possibilities continues to grow. “The LBT can make images sharp enough to resolve a football at a distance of 4,000 miles,” said Dr. John Hill, LBT’s technical director. “So if it weren’t for the curvature of the Earth, you could use it to watch Steelers games in Pittsburgh.”

telescopes

Courtesy gmt.org

(Reprinted from Tucson Weekly, by Jonathan Lowe. Also wrote a cover article for Sky & Telescope.)

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We’ll Always Have Paris

Paris

We’ll always have Paris…Texas.”

Just got to Greenville SC after a drive from Tucson (and a cruise to Alaska.) Observations:
1) There are no bears or whales to be seen in Alaska from a cruise ship, although the staff frequently sighted many from the bridge and excitedly told everyone to look either to port or starboard. (Favorite awe shucks: “Must have gone under the ship to mate with Nessie.”)
2) The only calving of glaciers to be seen from a cruise ship are on the videos they attempt to sell you (along with photos of you taken by them every chance they get…plus liquor.) The ship (Holland America) turned around some four miles from the glacier, and didn’t approach another for safety reasons “because of icebergs” (although in the publicity shots you see the ship surrounded by icebergs.) I think this is to sell more shore excursions. Indeed, I took a shore excursion to one of the glaciers, but had to run part way to it due to “time constraints.” (The driver joked, “You know what the bears call tourists five minutes late for the bus? Lunch.”)  Again, and alas, no calving or bears. Or bald eagles. (“Look, there’s one! See it?” Everyone in unison: “Nope.”)
3) Cruise ships burn the equivalent of two swimming pools of fuel every week (yes, with a deep end suitable for the Olympics), and there are hundreds of such ships, along with dozens of tankers transporting the oil from the Persian gulf. Not to mention thousands of jets and millions of cars in operation at any one time. In fact, we’ve gone through millions of years of fossil fuels in one century, and this last year was the hottest on record. So why can’t I see one sheet of ice fall from a glacier while being asked to buy videos and tee shirts featuring whales and bears and eagles…and rum drinks?
4) Alaska is wild and cold and huge. Driving across Texas is wild and hot and (according to Sarah Palin) “a cute little place.” That cute little place took the better part of two days to traverse nonetheless, with drivers who imagine themselves NASCAR racers (complete with tee shirts.) I heard on the news that Texas needs so many new prisons they’re thinking of letting reckless drivers and drug dealers out early to save on bed costs.  Why not let loose the serial killers too? Sure, just take away their driver’s licenses and put them to work in road construction. Then the DUIs and NASCAR wannabes will take them out, two jailbirds with one stone(d). Better yet, we should charge admission to prisons for tourists, like at theme parks. Bring the kids, make a picnic of it. A year in fees of $20 a head would pay to keep Gitmo open for one more week.
5) I never made it to Paris, and who knows, maybe I never will. Never got married either. (Nor did my sister, with whom I traveled to Alaska and across the country…she’s nine years older than I, legally blind, and can’t drive OR spot wildlife.) A girlfriend once told me that she couldn’t wait until I became rich and famous as a writer. The next day I learned that she meant it, literally. She couldn’t wait, and didn’t. Me? I’m still waiting. Next up, my memoirs. Fiction, I think, mostly. My real life is just too boring. In my fictional life, I married Kim Kashkashian (violinist), went to Paris, bought a big house with a tall white picket fence for the bald eagles to land on…and to keep out the bears. We have a yacht bigger than James Patterson’s, and as it roars past the glacier, engines burning its $20 per gallon fuel, huge blue slabs of ice fall into the aquamarine waters. And then, inexplicably, a charming and friendly whale, rising from beneath us, (fresh from his tryst with Nessie), smiles on us and breaks one of the floes into fragments small enough for our rum drinks.Sitka

TFOB

Wallow Fire Blues

wallow fireIt’s so sad, the fire around Alpine AZ…I was just telling my sister what an incredible place that is…so pristine, little traffic, vast forests…I saw a wolf and then a family of 7 deer in the road.  I had just driven through there on my way back to SC for the summer, and was warned by someone at a gas station not to take highway 191 up to i40 because of all the switchbacks (“it’s a huge waste of time” he said).  I took the road anyway, and was amazed….one of the most beautiful roads I’ve ever seen.  Didn’t pass a single car the first 50 miles, heading north through mountain wilderness.  When I came to Alpine it was so incredible I was even wondering how it might be possible to live there, and then I pick up the paper here in SC the other day, and see that it’s about to be engulfed in flames. So sad. I just can’t imagine driving back that way and seeing all those trees now only ash.  I thought of Avatar, and hope this wasn’t caused by some careless camper or arsonist.

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arizona forest

TFOB