See the sun’s corona in full


This photograph of the sun, taken by the Atmospheric Imaging Assembly instrument on NASA’s Solar Dynamics Observatory, shows how image processing techniques can reveal the faint, inner corona. At the sun’s limb, prominences larger than the Earth arc into space. Bright active regions like the one on the sun’s face at lower center are often the source of huge eruptions known as coronal mass ejections.

Solar eclipse chasers are drawn to the fleeting moments of totality, when the sun’s outer atmosphere — called the corona — becomes visible to the naked eye. Now, thanks to an instrument onboard NASA’s Solar Dynamics Observatory as well as a new image-processing program, that moment can last 24 hours a day, seven days a week.

The corona is hotter than the sun’s surface, but so tenuous that its light is overwhelmed by the much brighter solar disk. Therefore it is only visible from Earth when the sun is blocked, such as during an eclipse.

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SDO was launched last February on a mission to study the sun and its influence on Earth and near-Earth space. Even before the mission, solar astronomers didn’t have to wait around for solar eclipses and clear skies to get a view of the corona — but their tool of choice, called a coronograph, partially blocks the area immediately surrounding the sun, leaving only the outer corona visible. The effect is akin to holding your hand in front of your face as you drive into the sun.

The AIA allows astronomers to “follow the corona all the way down to the sun’s surface,” Leon Golub of the Harvard-Smithsonian Center for Astrophysics, said in a statement from the Harvard-Smithsonian Center for Astrophysics, or CfA. The instrument essentially fills the gap created by the limitations of the coronograph.

CfA astronomers Steven Crammer and Alec Engell developed a computer program for processing the AIA images of the corona. These processed images, including the one above, imitate the blocking-out effect that occurs during a total solar eclipse, revealing the highly dynamic nature of the inner corona.

The resulting images provide a full frontal view of the sun and its corona, highlighting the ever-changing connections between the gas captured by the sun’s magnetic field and the gas escaping into interplanetary space.

The sun’s magnetic field molds and shapes the corona. Hot solar plasma streams outward in vast loops larger than Earth before plunging back onto the sun’s surface. Some of the loops expand and stretch bigger and bigger until they break, belching plasma outward.

These belches of plasma, called coronal mass ejections, are responsible for creating brilliant auroral displays and can even knock out power grids, communications satellites, and pose a risk to astronauts on the International Space Station.

In August, the SDO captured one such eruption directed right at Earth. The eruption was the first in what is expected to be increasing solar activity as the sun ramps up from a low in its 11-year activity cycle.

The processed AIA images will be used to study the initial eruption phase of coronal mass ejections as they leave the sun and test theories of solar wind acceleration based on magnetic reconnection.

For more on the sun and space weather check out the stories below:

* Huge solar explosions can rock the entire sun * A ‘snake’ slithers across the sun * Solar outbursts? No worries for spacewalk * New solar observatory to unlock sun’s mysteries * The sun is yours … on a computer * ‘Spectacular’ sights come from solar probe

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John Roach is a contributing writer for Connect with the Cosmic Log community by hitting the “like” button on the Cosmic Log Facebook page or following’s science editor, Alan Boyle, on Twitter (@b0yle).


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