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Image name: extended_corona_8_may_92_enhanced_red.png (click image to enlarge)
Image size: 232.442 KB (700x498)
Date submitted: 08-Sep-1995
The sun in x-rays on 8 May 1992. This picture reveals the corona, or
extended outer atmosphere, of the sun. Note that the normally bright disk of
the sun is dark. The reason is that the solar surface has a temperature of
5000 degress, too cool to produce x-rays. The corona, on the other hand, has
temperatures of 1 to 3 million degrees -- hot enough to radiate x-rays. The
reason the sun has such a hot outer atmosphere is one of the great unsolved
problems of astrophysics.
The curvilinear structures seen in the picture map out the magnetic field of
the corona at places where the magnetic field lines are connected to the sun
at both ends, like the magnetic field of the earth. The dark area at the top
(north pole) of the sun is a so-called "coronal hole". Here the magnetic
field lines stretch out into interplanetary space so the hot coronal gases
are free to escape along the field lines and the density is lower. This
picture was taken by the Soft X-ray Telescope on the Japan/US/UK Yohkoh
("sunbeam" in Japanese) mission which was launched on 30 August 1991.
