Even today he would be a bold
astronomer who would profess to say with certainty whether the
smallest stars we can photograph are at the boundary of the
system. Before we decide this point we must have some idea of the
form and distance of the cloudlike masses of stars which form our
great celestial girdle. A most curious fact is that our solar
system seems to be in the centre of this galactic universe,
because the Milky Way divides the heavens into two equal parts,
and seems equally broad at all points. Were we looking at such a
girdle as this from one side or the other, this appearance would
not be presented. But let us not be too bold. Perhaps we are the
victims of some fallacy, as Ptolemy was when he proved, by what
looked like sound reasoning, based on undeniable facts, that this
earth of ours stood at rest in the centre of the heavens!
A related problem, and one which may be of supreme importance to
the future of our race, is, What is the source of the heat
radiated by the sun and stars? We know that life on the earth is
dependent on the heat which the sun sends it. If we were deprived
of this heat we should in a few days be enveloped in a frost which
would destroy nearly all vegetation, and in a few months neither
man nor animal would be alive, unless crouching over fires soon to
expire for want of fuel.
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