A medical X-ray technique has been adapted to produce the first detailed map of the structure of the Sun’s outermost layer, the corona, created from direct observations.
Tomography, a technique with multiple medical applications including CAT scans, uses a series of images taken from many different angles to reconstruct a 3-dimensional map of a patient’s body.
"This is a breakthrough for scientists trying to understand the corona and the solar wind. We’ve been attempting to apply tomography to the solar corona for more than 30 years but it’s proved very difficult and very inaccurate until now. The new technique that I’ve developed is only in its infancy but shows great potential for areas of research like space weather," said Dr Morgan, of the University of Aberystwyth.
In applying tomography to the Sun, scientists have been faced by two major problems: firstly, they can’t see through the Sun to measure the corona on the far side, therefore nearly half their data is ‘missing’. Secondly, the outermost areas of the corona are more than a thousand times fainter than the regions near the Sun, which introduces huge potential errors to observations.
Dr Morgan has found a new way of processing coronal images, called Qualitative Solar Rotational Tomography (QSRT), to eliminate the steep drop in brightness and associated errors. He has then applied the technique to a series of images taken with the SOHO spacecraft’s LASCO instrument, so that the whole of the corona is mapped as the Sun’s rotation brings the ‘missing’ areas into view. The maps are 5 times more detailed than previous tomographical studies of the Sun and Morgan believes that they have the potential for 20 times better resolution in the future.
"I’ve now produced maps of the corona over almost a whole cycle of solar activity, so we can now see in unprecedented detail how structures develop and evolve in three-dimensions. The maps have produced some interesting results: for instance we’ve observed large areas of dense structures when the Sun is most active that are not predicted by current computer models. We’ve also found evidence that inner regions of the corona rotate at different speeds."
The technique is already being used by scientists at the Institute of Maths and Physics at Aberystwyth University to interpret their radio-wave observations of the solar wind. Dr Morgan, together with colleagues at the Institute of Astronomy at the University of Hawaii, is also using the maps to interpret ultraviolet observations of the corona.
The results will be presented by Dr Huw Morgan at the RAS National Astronomy Meeting in Belfast on Tuesday 1st April.
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