Star gazers get sharpest view yet of sun

By LIDIA WASOWICZ, UPI Senior Science Writer  |  Nov. 13, 2002 at 3:26 PM
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Ushering in a new era in solar telescopes, the premiere of a powerful sun-watching instrument has provided astrophysicists with the sharpest, most detailed view yet of the 4.5 billion-year-old superheated ball of gas at the center of our solar system.

Equipped with the latest adaptive optics technology expected to revolutionize star-gazing tools, the Royal Swedish Academy of Sciences' 1-meter (3.25-foot) solar telescope atop an extinct volcano in Spain's Canary Islands has captured the world's most revealing images of the sun, scientists reported Wednesday.

Among the newly uncovered solar features are mysterious dark structures within sunspots. These solar magnetic storms -- which appear as odd-shaped inky blobs splattered across the sun's surface -- can wreak havoc with radio communications, power distribution, signal systems for trains and satellites and other vital earthly activities.

The Swedish instrument, installed March 2, 2002, and fully operational on May 21, has a resolution unmatched by any other solar telescope -- 1,200 times crisper than the focus of human eyes with normal 20/20 vision.

The telescope enables scientists to examine features as small as 100 kilometers (63 miles) on the sun's surface -- an extraordinary feat considering the target has a diameter of some 1.39 million km (865,000 miles) and is an average 150 million km (93 million miles) away, scientists told United Press International.

"The telescope is the most highly resolving telescope ever built," said Göran Scharmer, professor and director of the Swedish academy's Institute for Solar Physics in Stockholm. "This telescope, as well as the adaptive optics system (both of which have been developed by our institute) were absolutely crucial to this discovery."

John Thomas of the Department of Physics and Astronomy and Mechanical Engineering at the University of Rochester in New York said the findings "herald the quality of data to be expected from a new generation of solar telescopes."

The images and movies collated from two months of daily sunrise-to-sunset observations expose unprecedented details of a strange and powerful phenomenon that has been under the telescope for nearly 400 years yet continues to confound astronomers.

Sunspots -- which captured researchers' attention after the Italian scientist Galileo Galilei spotted them with his new telescope in 1610 -- occur when a concentrated portion of the solar magnetic field pokes through the surface, pockmarking the sun with Earth-sized spots. These transitory patches are cooler -- and darker -- than the surrounding solar surface because the magnetic field packed within blocks the searing gas rising from the star's interior.

At times flaring up to 80,400 km (50,000 miles) in diameter, sunspots often are large enough to be visible to the naked eye. Lasting for days or even weeks, they meander across the sun's surface, contracting and expanding as they come and go in a cycle that reaches maximum numbers every eleven years on average.

The sunspot snapshots, published in the Nov. 14 issue of the British journal Nature, expose never-before-seen features in a solar region with magnetic fields strong enough to wreak havoc with telecommunications and satellite operations on Earth.

"Sunspots have been observed with telescopes for four centuries, their existence is an intellectual challenge to us," Scharmer told UPI. "There are also speculations that solar activity may affect our climate ... What is clear, however, is that radio communications, power distribution, signal systems for trains, satellites, etc. are all affected by solar activity. The origin of all this is from sunspots."

The new images bring to light long-hidden, thin smoky cores within the brilliant thread-like structures that surround the darkest part of a sunspot in its outer region or penumbra.

Researchers called this an unexpected discovery, the full impact of which remains to be determined.

"In order to understand sunspot penumbrae, we need some distinct 'signatures' that allow us to distinguish between different (theoretical) explanations and thus advance our understanding," Scharmer told UPI. "If we see only penumbra filaments as unresolved thin and fuzzy threads, then we do not have so much evidence to build on. The dark cores in filaments provide such a 'signature' that we can use to test theories on."

The penumbra, a dynamic structure in constant motion, is thought to play a key role in keeping sunspots from disintegrating. Here, fundamental physical processes occur in the solar photosphere, the sun's luminous surface. Physicists cannot yet explain these forces and hope a closer look will be a telling one.

The findings are important because scientists have known for many years that basic processes in the solar atmosphere take place on scales smaller than 100 km but were unable to catch a glimpse of anything so tiny. With its first striking results, the Swedish telescope opened a window onto this world, researchers told UPI. They called the achievement a breakthrough in observational solar physics.

Physicists have had a particular interest in sunspots, long regarded as a test bed for studying how conducting liquids, such as plasmas or liquid metals, behave in magnetic fields, noted lead study author Dan Kiselman, research associate at the AlbaNova University Center in Stockholm.

"With the conditions in the universe being so extreme, we cannot perform laboratory experiments to investigate such phenomena," Scharmer told UPI. "The sun is an astrophysical laboratory in our immediate proximity, but we need excellent observations to support the theoretical framework that we build from such observations and that we wish to apply to other astrophysical objects."

The main obstacle to getting a clear view of such processes from Earth is the turbulent mixture of cold and warm air in the atmosphere that blurs and deforms the telescopic images. Scientists have scoured the globe in search of sites with the most stable air that would allow the sharpest pictures possible. The Swedish observatory on the secluded island of La Palma meets most of these criteria, providing the best-known site for solar observations, researchers said.

Yet even there, the conditions are imperfect, so the scientists turned to a new technology called adaptive optics. The technique can compensate for the atmosphere's blurring effects and enable astronomers to see and photograph solar details of smaller size than previously possible.

The telescope, operated by the Swedish academy's Institute for Solar Physics, is designed to mitigate the image-smearing effects of the turbulent terrestrial atmosphere. It is the first solar instrument to incorporate an adaptive mirror that shifts shape 1,000 times a second to adjust to the rapidly changing distortions of the image. The feature makes the images the sharpest ever of the sun, said Thomas, who analyzed the findings in an accompanying commentary.

"Having been responsible for the construction of the telescope, to see the first ... images was a very emotional moment," Scharmer recalled. "My first impressions was that of beauty and joy (and relief)."

Adaptive optics represent the future of large telescopes, he added, noting the technique has already demonstrated dramatic improvements of image quality on several large night-time telescopes around the world.

The team plans to continue peering at sunspots from different angles. By spring, the researchers will install an improved adaptive optics system that should give them a more sophisticated view of the penumbra.

"Observing and understanding fine-scale structures on the sun is important, not only for our knowledge of the sun but in astrophysics generally," Thomas told UPI. "(Now) great ingenuity and new technology (are enabling) us to observe such fine details from the ground."

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