After a relatively long pause I could perform two short astrophotographic sessions on the last summer nights. I chose two star clusters, first a typical globular cluster: the Great Cluster in Hercules, and as a second project, an open cluster: The Double Cluster in Perseus.
Star Clusters are very large group of stars. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds to millions of old stars which are gravitationally bound, while open clusters, more loosely clustered groups of stars, generally contain fewer than a few hundred members, and are often very young. Open clusters become disrupted over time by the gravitational influence of giant molecular clouds as they move through the galaxy, but cluster members will continue to move in broadly the same direction through space even though they are no longer gravitationally bound; they are then known as a stellar association, sometimes also referred to as a moving group.
The Great Globular Cluster in Hercules or Messier 13 and its surrounding region
Image Integration: 0.6 hours
more Info here.
Messier 13 (M13), also designated the Great Globular Cluster in Hercules, is a globular cluster of about 300,000 stars in the constellation of Hercules and is one of the best-known clusters of the northern-hemisphere.
Globular clusters are spherical collections of stars that orbit a galactic core as satellites. There are about 150 to 158 currently known globular clusters in the Milky Way, with perhaps 10 to 20 more still undiscovered.
Due to its apparent magnitude the Cluster is barely visible with the naked eye on a very clear night. Its diameter is about 23 arc minutes and it is readily viewable in small telescopes.
The Arecibo message of 1974, which contained encoded information about the human race, DNA, atomic numbers, Earth's position and other information, was beamed from the Arecibo Observatory radio telescope towards M13 as an experiment in contacting potential extraterrestrial civilizations in the cluster.
Two small background galaxies are also visible on the upper left corner of the image: the bigger NGC 6207 is a spiral galaxy located about 30 million light-years away from Earth. Its diameter is 34,000 light-years. The smaller IC 4617 is also a spiral galaxy, located about 496 million light-years away and has a diameter 175,000 light-years which is about the size of our home galaxy, the Milky Way.
The Double Cluster in the constellation Perseus
Image Integration: 0.8 hours
More Infos here.
The Double Cluster is the common name for the open clusters NGC 869 and NGC 884 which are close together in the constellation Perseus. Both visible with the naked eye, NGC 869 and NGC 884 lie at a distance of 7500 light years.
NGC 869 has a mass of 3700 solar masses and NGC 884 weighs in at 2800 solar masses; however, later research has shown both clusters are surrounded with a very extensive halo of stars, with a total mass for the complex of at least 20,000 solar masses. Based on their individual stars, the clusters are relatively young, both 12.8 million years old.
There are more than 300 blue-white super-giant stars in each of the clusters. The clusters are also blueshifted, with NGC 869 approaching Earth at a speed of 39 km/s (24 mi/s) and NGC 884 approaching at a similar speed of 38 km/s (24 mi/s).
--source of the astronomical informations and texts: wikipedia