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