Yohkoh Solar X-ray Cycle
Credit: G.L. Slater and G.A. Linford; S.L. Freeland; the Yohkoh Project

Solar X-ray Cycle

The solar corona is a region of magnetically confined gas surrounding the sun. The corona is incredibly hot, reaching temperatures above 2 million degrees, hot enough to produce X-rays. Scientists believe that the solar magnetic field heats the corona; because the solar magnetic fields undergoes an 11-year solar activity cycle, the temperature and brightness of the solar corona also undergoes variations with this activity cycle. This variation is beautifully illustrated in the above images of the solar corona, obtained by the Soft X-ray Telescope on the Yohkoh solar observatory. The corona looks bright, while the solar surface (which, at 6000 degrees, is too cool to produce X-rays) appears dark. The 12 solar X-ray images shown above were obtained between 1991 and 1995, and show the decrease in solar coronal brightness (by about a factor of 100) as the sun goes from an "active" state to a less active state. Yohkoh has just celebrated 10 years in orbit, observing the sun from space for nearly one complete solar cycle.

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Each week the HEASARC brings you new, exciting and beautiful images from X-ray and Gamma ray astronomy. Check back each week and be sure to check out the HEAPOW archive!

Page Author: Dr. Michael F. Corcoran
Last modified September 14, 2001