Blending of an eclipse image (from the High Altitude Observatory) with a Yohkoh X-ray image (from the Yohkoh Science Team).
Click on image for full size
Image courtesy of the High Altitude Observatory, National Center for Atmospheric Research (NCAR), Boulder, Colorado,
The Solar Corona
Rising above the Sun's chromosphere ,
the temperature jumps sharply from a few tens of thousands of kelvins
to as much as a few million kelvins in the Sun's outer atmosphere,
the solar corona. Understanding the reason the Sun's corona
is so hot is one of the many challenges facing solar physicists today.
Because of the very high temperatures, the corona emits high
energy radiation and can be observed in X-rays. The Earth's
atmosphere absorbs X-rays, but satellites above the atmosphere,
such as the Yohkoh spacecraft, can observe the Sun in these
wavelengths. Shown on the left is a blending of a Yohkoh
X-ray image (reddish colors) with an
eclipse image taken by
the High Altitude Observatory (gray-white colors) on November 3, 1994.
Near the poles of the Sun, the corona is dark for both X-rays and white light.
These regions are coronal holes and are
the source of the solar wind that extends out into
interplanetary space. The scattered white light
shows the density of plasma in the corona. The large white regions extending
out far from the Sun are helmet streamers,
where the solar plasma has been trapped by the Sun's magnetic field.
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