cold hydrogen gas in these clouds is in the form of molecules, which is why
they are also called molecular clouds. The hydrogen gas is mixed with dust,
which is responsible for the light absorption. Larger dark nebulae are called
giant molecular clouds and can measure several hundred light years. They are
regions of active star formation, an example of such a giant cloud is the Orion
OB 1 region. These clouds contain several million times the mass of the
At the top of our mosaic in
the center of the image is the planet Jupiter, surrounded by garland-like dark
clouds, see also the image version with object markers. North (above) the
bright blue star (Theta Oph) at the left edge of the image is
Barnard 72, the snake nebula. To the right below
Barnard 72 is a small, roughly kidney-shaped dark cloud, Barnard 68, which is one of the densest dark clouds with
an absorption in the visual spectral range of nearly 20 magnitudes.
South of Theta Ophiuchus lies a large complex of dark clouds that have
Barnard catalog numbers from 59 to78. This complex
is also known as the pipe nebula.
Ophiuchusis a beta Cephei type variable star. It is assigned to spectral
type B0 IV and shines in deep blue color. Just right above Theta is the star HD
156 992, which has spectral class K3 and shines in a rich yellow-orange color.
Furthermore the mosaic shows a larger number of globular clusters, among others
NGC 6287, 6325, 6284, 6355, 6293, 6116. The
brightest globular cluster in the image is Messier
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