|Documentation > SXT Observation Notes > this page|
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.