Researchers take the sun's temperature

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NEWCASTLE, England, Feb. 4 (UPI) -- British researchers say they have begun to unravel the mystery of why a part of the sun's atmosphere is much hotter than its surface.

Scientists at Northumbria University along with researchers from the University of Sheffield and Queen's University Belfast, report using cutting-edge solar-imaging technology to observe the Sun's chromosphere -- a region of the Sun's atmosphere sandwiched between its surface (photosphere) and outer layer (corona).

Scientists have long been puzzled by why some stars possess a corona almost 200 times hotter than their photosphere despite being further away from the heat source at the star's core.

The commonly accepted theory is that the increased temperature is due to magnetohydrodynamic waves that pump energy generated below the star's surface to the outer layers of the sun's atmosphere.

The researchers used a British-designed dedicated solar-imaging telescope to obtain some of the highest resolution images of the chromosphere ever gathered, allowing them to estimate the speed and power of the waves and the amount of energy they transport.

"Stars generate heat through thermonuclear reactions in their core and the temperature decreases towards the star's surface," Northumbria researcher Richard Morton said. "However, a significant number of stars have higher temperatures at the outer edges of their atmospheres than they do on their surface.

The new study suggests waves could be responsible for transporting energy from below the solar surface, out through the chromosphere and into the corona, heating the outer layers in excess of 1 million degrees, he said.

"Our observations have permitted us to estimate the amount of energy transported by the magnetic waves, and these estimates reveal that the waves' energy meets the energy requirement for the unexplained temperature increase in the corona."