(Jewel Box, NGC 4755)
The constellation »Southern Cross«
holds two more very interesting but completely different astronomical objects: the
»Coal Sack« and the »Jewel Box«.
The »Jewel Box« received its name by John Herschel (1792-1871), the son
of the famous astronomer Wilhelm Herschel. It is the maybe most beautiful open cluster
in the sky. Not using any auxiliary device only a small single star is visible. But
even with a small, simple telescope the spot separates into more then 50 single stars
that shine in various colours like jewels. On an average they are about 5000 light-years
away from our earth.
Only a few angular seconds above one can find a large dark nebula, the so called
»Coal Sack«. Due to its position right in front of the Milky Way it looks like a hole
in the sky. Dark Nebulae are, like all other nebulae, accumulations of gas and dust,
that are not, and this is the difference, lightened by stars in their neighbourhood or
their interior. They conceal the light of the stars behind them. The less stars can be
seen inside the dark region therefore the closer the nebula is to our earth. The
distance to the »Coal Sack« is estimated to about 400-500 light-years, and its size
to a total of 60-70 light-years in diameter.
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