If this fifty per cent
increase of distance for each lower magnitude of stars were
certain and constant, the stars of the eighth magnitude would be
3000 billion miles away, and stars of the sixteenth magnitude
would be 100,000 billion miles away; and there are still two
fainter classes of stars which are registered on long-exposure
photographs. The mere vastness of these figures is immaterial to
the astronomer, but he warns us that the method is uncertain. We
may be content to conclude that the starry universe over which
our great telescopes keep watch stretches for thousands, and
probably tens of thousands, of billions of miles. There are
myriads of stars so remote that, though each is a vast
incandescent globe at a temperature of many thousand degrees, and
though their light is concentrated on the mirrors or in the
lenses of our largest telescopes and directed upon the
photographic plate at the rate of more than 800 billion waves a
second, they take several hours to register the faintest point of
light on the plate.
When we reflect that the universe has grown with the growth of
our telescopes and the application of photography we wonder
whether we may as yet see only a fraction of the real universe,
as small in comparison with the whole as the Babylonian system
was in comparison with ours.
Pages:
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37