turtle
January 18, 2017

‘Turtle’ the size of two Earths spotted in sunspot

We have all picked out shapes in the clouds, but this is somewhat next-level: A dark turtle shape twice the size of Earth has been spotted over the surface of the sun.

Groundbreaking images from the ALMA radio telescope in Chile show the sunspot, which is almost two times Earth's diameter, looking like a black turtle swimming across a burning sea.

The dark area is cooler than its surroundings, and was created when the sun's magnetic field lines warped and broke through the surface of plasma in the chromosphere. The chromosphere is located just above the photosphere - the visible surface of the sun.

Map of the sun at 1.25 mm taken using the ALMA telescope with a "fast-scanning technique" that uses only one of the observatory's 66 antennas, creating a low-resolution map of the disk in a few minutes. Credit: ALMA (ESO/NAOJ/NRAO)

Map of the sun at 1.25 mm taken using the ALMA telescope with a "fast-scanning technique" that uses only one of the observatory's 66 antennas, creating a low-resolution map of the disk in a few minutes.
Credit: ALMA (ESO/NAOJ/NRAO)

Understanding the physics of the sun

The ALMA telescope usually probes radio waves released by some of the most distant galaxies in the universe.

However in late 2015, when the 'turtle' was spotted, it picked up waves released by the chromosphere and returned the images using radio waves at 2.5 and 3 millimeters, which show conditions at two different chromosphere depths.

The development could help with further understanding of the physics of the sun.

"We're accustomed to seeing how our sun appears in visible light, but that can only tell us so much about the dynamic surface and energetic atmosphere of our nearest star," said Tim Bastian, an astronomer at the National Radio Astronomy Observatory in Virginia.

"To fully understand the sun, we need to study it across the entire electromagnetic spectrum, including the millimeter and submillimeter portion that ALMA can observe."

ALMA's antennas were built to enable observation of the sun's intense light, but this was the first time radio emissions from our sun had been measured. Partnered with the European Southern Observatory, it is the first observatory able to investigate the sun.

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Image credit: ALMA (ESO/NAOJ/NRAO)