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WHY IS THE SOLAR CORONA HOT?

Last Updated on Sunday, 02 May 2010 13:06
Published on Friday, 25 February 2005 00:00

 

During the total solar eclipse on 11 August, millions of ordinary people will have a rare opportunity (weather permitting) to see for themselves the Sun's outer atmosphere, called the "corona". Amazingly, the temperature of this faintly glowing gas is a million degrees or more. Somehow, energy from the Sun heats the corona. Exactly how the process works remains something of a mystery, but on Thursday 12th August, Dr Philippa Browning of the University of Manchester Institute of Science and Technology (UMIST), will round up the current state of expert knowledge on the subject at the UK Solar Physics Meeting in Guernsey, Channel Islands.

"During a total eclipse, we can actually see that the corona is not at all smooth but contains a lot of structure - rays and streamers, for example", says Dr Browning. "However, what we can see with our eyes is only a small part of the story. The corona emits x-rays far more strongly than visible light. Fortunately for life on Earth, the x-rays do not penetrate the Earth's atmosphere. But it means that the corona is best studied from space."

X-ray images of the Sun from satellites such as SOHO and YOHKOH show, better than visible images, that the corona is highly structured and also very dynamic as a consequence of the strong magnetic field, which confines and controls the hot gas - and it is very hot gas indeed.

One of the most striking aspects of the corona is its temperature - around a million or more degrees - compared with the familiar yellow surface of the Sun which registers a much lower temperature of only a few thousand degrees. It is because of its very high temperature that the corona emits x-rays. No-one as yet fully understood why the corona is so hot. However, it is clear that the magnetic field plays a key role.

Solar experts now generally believe that energy from below the solar surface, carried by moving gas, is transmitted into the corona where it is stored as magnetic energy. Within the corona, this magnetic energy is then converted into heat. Some scientists take the view that the energy is carried by magnetic waves, others favour magnetic fields associated with steady electrical currents. As a result, the question "Why is the corona hot?" remains a topic of considerable controversy.

NOTE

Relevant images of the Sun, and further links may be found on the web site for the SOHO solar space observatory, at: http://sohowww.nascom.nasa.gov/

CONTACT Dr Philippa Browning
Dept. of Physics, UMIST, Manchester
Phone: (0)161 200 3912
E-mail:, This email address is being protected from spambots. You need JavaScript enabled to view it.

CONTACTING THE PRESS ROOM AND PRESS OFFICERS AT THE UK SOLAR PHYSICS MEETING AND NATIONAL ASTRONOMY MEETING 9 - 13 AUGUST

Except on Wednesday 11th August, please try press room numbers before calling mobiles.

Press room phone numbers: 01481 710889, 01481 712834 and 01481 712936 Press room fax number: 01481 713044.

Mobile phone nos.:
Jacqueline Mitton (RAS Press Officer): 0370-386133
Peter Bond (RAS Press Officer, Space Science) : 0411-213486
Charlotte Allen (PPARC Press Officer): 07899-945493


Issued by:
Dr Jacqueline Mitton, RAS Press Officer
Phone: Cambridge ((0)1223) 564914
FAX: Cambridge ((0)1223) 572892
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.