This is an
image of the Sun's chromosphere, from chromos, the Greek word for
color. This layer of the Sun can be detected with a telescope that looks
for the red light it gives off, called Hydrogen-alpha light. The
temperature of the chromosphere is
about 6000 to 50000 degrees C. In this image cooler features, like
filaments, appear darker because they
do not give off as much red light.
Image Credit: NOAA/SEL/USAF