Now that observatories are
multiplying in the southern hemisphere, the great austral
``Coal-sack'' will, no doubt, receive attention proportioned to its
importance as one of the most significant features of the sky. Already
at the Sydney Observatory photographs have shown that the southern
portion of this Dead Sea of Space is not quite ``bottomless,''
although its northern part defies the longest sounding lines of the
astronomer.
There is a similar, but less perfect, ``coal-sack'' in the northern
hemisphere, in the constellation of ``The Swan,'' which, strange to
say, also contains a well-marked figure of a cross outlined by stars.
This gap lies near the top of the cross-shaped figure. It is best seen
by averted vision, which brings out the contrast with the Milky Way,
which is quite brilliant around it. It does not, however, exercise the
same weird attraction upon the eye as the southern ``Coal-sack,'' for
instead of looking like an absolute void in the sky, it rather appears
as if a canopy of dark gauze had been drawn over the stars. We shall
see the possible significance of this appearance later.
Just above the southern horizon of our northern middle latitudes, in
summer, where the Milky Way breaks up into vast sheets of nebulous
luminosity, lying over and between the constellations Scorpio and
Sagittarius, there is a remarkable assemblage of ``coal-sacks,''
though none is of great size.
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