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NAM 2008
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Royal Astronomical Society
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CONTACTS

Dr Huw Morgan
Institute for Astronomy
University of Hawaii
Institute of Maths and Physical Sciences
University of Wales
Aberystwyth
Tel: +44 (0)1970 628419
Website: http://www.ifa.hawaii.edu/users/hmorgan

Date: 1 April 2008

Ref.: PN 08/15 (NAM 06)

Medical X-ray technique unveils the Sun's corona

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. The results will be presented by Dr Huw Morgan at the
RAS National Astronomy Meeting in Belfast on Tuesday 1st April.

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.

IMAGES Images and animations can be found at:
   http://www.ifa.hawaii.edu/users/hmorgan/tomography/index-e.htm

NOTES FOR EDITORS

RAS NATIONAL ASTRONOMY MEETING

The RAS National Astronomy Meeting (NAM 2008) is hosted by Queen's
University Belfast. It is principally sponsored by the RAS and the STFC. NAM
2008 is being held together with the UK Solar Physics (UKSP) and
Magnetosphere, Ionosphere and Solar-Terrestrial (MIST) spring meetings.

SOLAR CORONA

The corona is the Sun's outer atmosphere and is the source of the solar
wind. It is very faint and is only visible during a total solar eclipse or
by using coronographs, which block out the bright disc of the Sun, or by
looking at it in high-energy wavelengths. Temperatures in the corona reach 1
million degrees Celsius, but the source of this heating is not fully
understood. The corona extends for 6 solar radii (4.17 billion kilometres)
beyond the Sun's visible surface (the chromosphere)

The solar wind is a stream of electrically-charged particles that is emitted
in all directions from the Sun's corona. It is made up of a roughly equal
number of protons and electrons, with a few heavier ions. The average speed
of the solar wind is 400 kilometres per second. High-speed solar wind
emanates from coronal holes, regions where magnetic field lines loop out
into space, allowing large quantities of solar atmosphere to escape.

Explosions at the Sun travel through space and often hit the Earth. These
energetic magnetic clouds can disrupt communication, power supplies and be a
major health hazard for astronauts and airline pilots. Understanding and
predicting these storms is a major goal of solar science. The ability to map
the whole 3D structure of the corona is a critical step towards achieving
this goal.

SOHO

SOHO (Solar & Heliospheric Observatory) is a joint ESA/NASA mission. SOHO's
orbit gives the spacecraft an uninterrupted view of the Sun. SOHO carries
twelve instruments that monitor the Sun's internal structure, its outer
atmosphere and the solar wind. Launched in 1995, SOHO's mission has now been
extended until December 2009.
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