This is an X-ray image of the sun, taken by the soft X-ray telescope
onbard the Yohkoh spacecraft. X-rays are produced in the corona
of the sun, not at it's surface, so X-ray images of the sun reveal
what's happening in the solar atmosphere.
The Yohkoh satellite is an observatory for studying X-rays and
gamma-rays from the Sun. Yohkoh is a project of the Institute
for Space and Astronautical Sciences, Japan; Yohkoh (the spacecraft)
was built in Japan, but the observing instruments have contributions
from the U.S. and from Great Britain.