New 3-D images of the Sun billed as the most detailed ever reveal a striking variety of features, astronomers announced today.
The trick in getting the 3-D pictures was to look not at the Sun's central regions but to peer toward the edge, or limb, of the Sun's disk. The effect is similar to staring down at a crowded sidewalk from above and seeing only heads, then looking toward the end of the block and, with a new perspective, being able to see entire bodies.
The images may help theorists understand why the Sun's radiation increases when the star is covered in dark sunspots.
"Until recently we thought of the solar photosphere as the relatively flat and featureless 'surface' of the Sun, punctuated only by an occasional sunspot," said Tom Berger, a solar physicist at the Lockheed Martin Solar and Astrophysics Lab. "Now we have, for the first time, imaged the three-dimensional structure of the convective 'granules' that cover the photosphere."
The images were generated by the Swedish 1-meter (3-foot) Solar Telescope on the Spanish island of La Palma. Berger led a study that was presented today at the American Astronomical Society's Solar Physics Division meeting in Laurel, Maryland.
The solar surface consists mostly of an irregular cellular pattern caused by temperature variations. The cells, called granules, are evidence of convection that transports heat to the surface -- just like boiling water on a stove.
Each granule on the Sun is about the size of Texas.
In the new images, sunspots and smaller dark "pores" are seen to be sunken into the surrounding granulation. The features had been inferred but never imaged directly.
Granulation in regions of smaller magnetic fields outside of sunspots is both raised up and has brighter walls than the granulation in non-magnetic regions. Bright structures near the limb of the Sun have been seen for centuries and are called faculae. Scientists think faculae brightness fluctuations correspond to increased solar radiation during periods of maximum solar magnetic activity.
At solar maximum -- the peak of an 11-year cycle -- the Sun has more sunspots, which tend to be dark. It might seem logical that less radiation would reach Earth. Instead, radiation increases. Scientists suspect the bright faculae near the limb of the Sun to be the source. Models suggest that small magnetic micropores act as tiny holes in the surface of the photosphere.
Figuring this out requires looking at the limb, or edge of the Sun.
When looking at center of the Sun's disk, astronomers see only the relatively cool "floors" of the micropores. When seen at an angle near the limb, the models predict that the "hot walls" of the magnetic holes should shine brightly compared to the relatively cooler surrounding granules. The new observations confirmed this.
Most of the bright structures seen are between 93 and 249 miles (150 and 400 kilometers) tall. Simultaneous measurements of the magnetic field establish that the bright faculae are exactly aligned with the magnetic fields, researchers said.
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