Overlying it is a deep layer of the vapours of the molten metals,
with a temperature of about 5500 degrees C.; and to this
comparatively cool and light-absorbing layer we owe the black
lines of the solar spectrum. Above it is an ocean of red-hot
hydrogen, and outside this again is an atmosphere stretching for
some hundreds of thousands of miles into space.
The significant feature, from our point of view, is the
"sun-spot"; though the spot may be an area of millions of square
miles. These areas are, of course, dark only by comparison with
the intense light of the rest of the disk. The darkest part of
them is 5000 times brighter than the full moon. It will be seen
further, on examining a photograph of the sun, that a network or
veining of this dark material overspreads the entire surface at
all times. There is still some difference of opinion as to the
nature of these areas, but the evidence of the spectroscope has
convinced most astronomers that they are masses of cooler vapour
lying upon, and sinking into, the ocean of liquid fire. Round
their edges, as if responding to the pressure of the more
condensed mass, gigantic spurts and mountains of the white-hot
matter of the sun rush upwards at a rate of fifty or a hundred
miles a second, Sometimes they reach a height of a hundred, and
even two hundred, thousand miles, driving the red-hot hydrogen
before them in prodigious and fantastic flames.
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