"Long before it's in the papers"
January 27, 2015


Astronomers take sharpest photos of night sky

Aug. 21, 2013
Courtesy of the University of Arizona
and World Science staff

As­tro­no­mers have de­vel­oped a new type of cam­era that al­lows sci­en­tists to take sharp­er im­ages of the night sky than ev­er be­fore.

The sci­en­tists at the Uni­vers­ity of Ar­i­zo­na, the Arcetri Ob­serv­a­to­ry near Flor­ence, Italy and the Car­ne­gie Ob­serv­a­to­ry has been de­vel­op­ing the tech­nol­o­gy for more than 20 years to over­come tur­bu­lence in the air above us that blurs star­light.

The Magellan Telescope re­vealed de­tails about the Ori­on neb­u­la. The back­ground im­age, tak­en with the Hub­ble Space Tel­e­scope, shows the Tra­pe­zi­um clus­ter of young stars (pink) still in the pro­cess of form­ing. The in­set pho­to re­veals the na­ture The­ta Ori C as two stars. (Cred­it: Laird Close and Ya-Lin Wu; NA­SA, C.R. O'Dell and S.K. Wong)

They de­ployed the lat­est ver­sion of these cam­er­as in the high des­ert of Chil­e at the Ma­gel­lan 6.5-meter tel­e­scope.

“It was very ex­cit­ing to see this new cam­era make the night sky look sharp­er than has ev­er be­fore been pos­si­ble,“ said Uni­vers­ity of Ar­i­zo­na as­tron­o­mer La­ird Close, the pro­jec­t's prin­ci­pal sci­ent­ist. 

“We can, for the first time, make long-exposure im­ages that re­solve ob­jects just 0.02 arc sec­onds across – the equiv­a­lent of a dime viewed from more than a hun­dred miles away. At that res­o­lu­tion, you could see a base­ball dia­mond on the moon.”

The two­fold im­prove­ment over past ef­forts rests on the fact that for the first time, a tel­e­scope with a wide pri­ma­ry mir­ror is be­ing used for dig­it­al pho­tog­ra­phy at its the­o­ret­i­cal res­o­lu­tion lim­it in wave­lengths of vis­i­ble light, the as­tron­o­mers said. A wave­length is the length of an in­di­vid­ual light wave.

“As we move to­wards shorter wave­lengths, im­age sharp­ness im­proves,” said Jar­ed Males, a NASA Sagan Fel­low at the uni­vers­ity. “Un­til now, large tel­e­scopes could make the the­o­ret­ic­ally sharpest pho­tos only in in­fra­red – or long wave­length – light, but our new cam­era can take pho­tos that are twice as sharp in the vis­i­ble light spec­trum.”

The im­ages are al­so said to be at least twice as sharp as what the Hub­ble Space Tel­e­scope can make, be­cause with its 21-foot wide mir­ror, the Ma­gel­lan tel­e­scope is much larg­er than Hub­ble with its eight-foot mir­ror. Mod­ern, pow­er­ful tel­e­scopes use curved mir­rors in­stead of lens­es.

Un­til now, Hub­ble al­ways pro­duced the best vis­i­ble light im­ages.

To over­come at­mos­pher­ic tur­bu­lence, which plagues earth-based tel­e­scopes, Close's team de­vel­oped a pow­er­ful “adap­tive op­tics” sys­tem that floats a thin curved glass mir­ror on a mag­net­ic field above the tel­e­scope's pri­ma­ry mir­ror. This so-called Adap­tive Sec­ond­ary Mir­ror can change its shape at 585 points on its sur­face 1,000 times a sec­ond, coun­ter­act­ing the blur­ring ef­fects of the at­mos­phere.

The new sys­tem, called Ma­gAO for Ma­gel­lan Adap­tive Op­tics, has al­ready made some disco­veries, pub­lished Sept. 21 in three sci­en­tif­ic pa­pers in the As­t­ro­phys­i­cal Jour­nal, the in­ves­ti­ga­tors added. As the sys­tem was be­ing tested and re­ceived what as­tron­o­mers call “first light,“ the team point­ed it to a fa­mous and well-stud­ied mas­sive star in the Great Ori­on Neb­u­la, which is vis­i­ble as smudge of light with bin­oc­u­lars.

Con­sid­ered young at about a mil­lion years old, this star, called The­ta 1 Ori C, has been pre­vi­ously known to be in fact a bi­na­ry or dou­ble star pa­ir made up of two stars called C1 and C2. Howev­er, the separa­t­ion be­tween the two is so small – about the av­er­age dis­tance be­tween Earth and Ura­nus – that as­tron­o­mers had nev­er been able to re­solve the fa­mous pa­ir in a di­rect tel­e­scope pho­to.

Once Ma­gAO and its vis­i­ble sci­ence cam­era called VisAO were point­ed to­wards The­ta Ori 1 C, the re­sults were im­me­di­ate, Close said. “I have been im­ag­ing The­ta 1 Ori C for more than 20 years and nev­er could di­rectly see that it was in fact two stars,” Close said. “But as soon as we turned on the Ma­gAO sys­tem it was beau­ti­fully split in­to two stars.”

* * *

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Astronomers have developed a new type of camera that allows scientists to take sharper images of the night sky than ever before. The scientists at the University of Arizona, the Arcetri Observatory near Florence, Italy and the Carnegie Observatory has been developing the technology for more than 20 years to overcome turbulence in the air above us that blurs starlight. They deployed the latest version of these cameras in the high desert of Chile at the Magellan 6.5-meter telescope. “It was very exciting to see this new camera make the night sky look sharper than has ever before been possible,“ said University of Arizona astronomer Laird Close, the project's principal scientist. “We can, for the first time, make long-exposure images that resolve objects just 0.02 arc seconds across – the equivalent of a dime viewed from more than a hundred miles away. At that resolution, you could see a baseball diamond on the moon.“ The twofold improvement over past efforts rests on the fact that for the first time, a telescope with a wide primary mirror is being used for digital photography at its theoretical resolution limit in wavelengths of visible light, the astronomers said. A wavelength is the length of an individual light wave. “As we move towards shorter wavelengths, image sharpness improves,“ said Jared Males, a NASA Sagan Fellow at the university. “Until now, large telescopes could make the theoretically sharpest photos only in infrared – or long wavelength – light, but our new camera can take photos that are twice as sharp in the visible light spectrum.“ These images are also at least twice as sharp as what the Hubble Space Telescope can make, because with its 21-foot wide mirror, the Magellan telescope is much larger than Hubble with its eight-foot mirror. Modern, powerful telescopes use curved mirrors instead of lenses. Until now, Hubble always produced the best visible light images. To overcome atmospheric turbulence, which plagues earth-based telescopes, Close's team developed a powerful “adaptive optics“ system that floats a thin curved glass mirror on a magnetic field 30 feet above the telescope's primary mirror. This so-called Adaptive Secondary Mirror can change its shape at 585 points on its surface 1,000 times a second, counteracting the blurring effects of the atmosphere. The new system, called MagAO for “Magellan Adaptive Optics,“ has already made some discoveries, published Sept. 21 in three scientific papers in the Astrophysical Journal, the investigators added. As the system was being tested and received what astronomers call “first light,“ the team pointed it to a famous and well-studied massive star in the Great Orion Nebula, which is visible as smudge of light with binoculars. Considered young at about a million years old, this star, called Theta 1 Ori C, has been previously known to be in fact a binary or double star pair made up of two stars called C1 and C2. However, the separation between the two is so small – about the average distance between Earth and Uranus – that astronomers had never been able to resolve the famous pair in a direct telescope photo. Once MagAO and its visible science camera called VisAO were pointed towards Theta Ori 1 C, the results were immediate, Close said. “I have been imaging Theta 1 Ori C for more than 20 years and never could directly see that it was in fact two stars,“ Close said. “But as soon as we turned on the MagAO system it was beautifully split into two stars.“