Here let us return to and see what more we know about the
photosphere--the sun's surface. It is from the photosphere that we have
gained most of our knowledge of the composition of the sun, which is
believed not to be a solid body. Examination of the photosphere shows
that the outer surface is never at rest. Small bright cloudlets come and
go in rapid succession, giving the surface, through contrasts in
luminosity, a granular appearance. Of course, to be visible at all at
92,830,000 miles the cloudlets cannot be small. They imply enormous
activity in the photosphere. If we might speak picturesquely the sun's
surface resembles a boiling ocean of white-hot metal vapours. We have
to-day a wonderful instrument, which will be described later, which
dilutes, as it were, the general glare of the sun, and enables us to
observe these fiery eruptions at any hour. The "oceans" of red-hot gas
and white-hot metal vapour at the sun's surface are constantly driven by
great storms. Some unimaginable energy streams out from the body or
muscles of the sun and blows its outer layers into gigantic shreds, as
it were.
The actual temperature at the sun's surface, or what appears to us to be
the surface--the photosphere--is, of course, unknown, but careful
calculation suggests that it is from 5,000° C. to 7,000° C. The interior
is vastly hotter. We can form no conception of such temperatures as must
exist there. Not even the most obdurate solid could resist such
temperatures, but would be converted almost instantaneously into gas.
But it would not be gas as we know gases on the earth. The enormous
pressures that exist on the sun must convert even gases into thick
treacly fluids. We can only infer this state of matter. It is beyond our
power to reproduce it.