Speaking roughly, we have reason, from the data so far available,
to believe that the stars of the Milky Way are situated at a
distance between 100,000,000 and 200,000,000 times the distance of
the sun. At distances less than this it seems likely that the
stars are distributed through space with some approach to
uniformity. We may state as a general conclusion, indicated by
several methods of making the estimate, that nearly all the stars
which we can see with our telescopes are contained within a sphere
not likely to be much more than 200,000,000 times the distance of
the sun.
The inquiring reader may here ask another question. Granting that
all the stars we can see are contained within this limit, may
there not be any number of stars outside the limit which are
invisible only because they are too far away to be seen?
This question may be answered quite definitely if we grant that
light from the most distant stars meets with no obstruction in
reaching us. The most conclusive answer is afforded by the measure
of starlight. If the stars extended out indefinitely, then the
number of those of each order of magnitude would be nearly four
times that of the magnitude next brighter. For example, we should
have nearly four times as many stars of the sixth magnitude as of
the fifth; nearly four times as many of the seventh as of the
sixth, and so on indefinitely.
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