Star clusters

M 15

Messier 15 or M15 (also designated NGC 7078) is a globular cluster in the constellation Pegasus. It was discovered by Jean-Dominique Maraldi in 1746 and included in Charles Messier's catalogue of comet-like objects in 1764. At an estimated 12.0 billion years old, it is one of the oldest known globular clusters.

M15 is about 33,600 light-years from Earth, and 175 light years in diameter. It has an absolute magnitude of -9.2, which translates to a total luminosity of 360,000 times that of the Sun. Messier 15 is one of the most densely packed globulars known in the Milky Way galaxy. Its core has undergone a contraction known as 'core collapse' and it has a central density cusp with an enormous number of stars surrounding what may be a central black hole.

R = 13 * 600 sec. bin1, G = 13 * 690 sec. bin1, B = 11 * 780 sec. bin1

Pixinsight 1.8, eXcalibrator, Lightroom.

M 15

M 13

Messier 13 (M13), also designated NGC 6205 and sometimes called the Great Globular Cluster in Hercules or the Hercules Globular Cluster, is a globular cluster of about 300,000 stars in the constellation of Hercules.

M13 was discovered by Edmond Halley in 1714, and catalogued by Charles Messier on June 1, 1764.

It is located at right ascension 16h 41.7m and declination +36° 28'. With an apparent magnitude of 5.8, it 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. Nearby is NGC 6207, a 12th magnitude edge-on galaxy that lies 28 arc minutes directly north east. A small galaxy, IC 4617, lies halfway between NGC 6207 and M13, north-northeast of the large globular cluster's center.

M13 is about 145 light-years in diameter, and it is composed of several hundred thousand stars, the brightest of which is a red giant, the variable star V11, with an apparent visual magnitude of 11.95. M13 is 25,100 light-years away from Earth.

R = 12 * 300 sec. bin1, G = 12 * 400 sec. bin1, B = 12 * 600 sec. bin1

Pixinsight 1.8, Photoshop.

M 13

M 92

Messier 92 (also known as M92, M 92, or NGC 6341) is a globular cluster of stars in the northern constellation of Hercules. It was discovered by Johann Elert Bode in 1777, then published in the Jahrbuch during 1779. The cluster was independently rediscovered by Charles Messier on March 18, 1781 and added as the 92nd entry in his catalogue. M92 is at a distance of about 26,700 light-years away from Earth.

M92 is one of the brighter globular clusters in the northern hemisphere, but it is often overlooked by amateur astronomers because of its proximity to the even more spectacular Messier 13. It is visible to the naked eye under very good conditions.

Among the Milky Way population of globular clusters, Messier 92 is among the brighter clusters in terms of absolute magnitude. It is also one of the oldest clusters. Messier 92 is located around 16×103 ly (4.9 kpc) above the galactic plane and 33×103 ly (10 kpc) from the Galactic Center. The heliocentric distance of Messier 92 is 26.7×103 ly (8.2 kpc). The half-light radius, or radius containing half of the light emission from the cluster, is 1.09 arcminutes, while the tidal radius is 15.17 arcminutes. It appears only slightly flattened, with the minor axis being about 89% ± 3% as large as the major axis.

R = 10 * 300 sec. bin1, G = 10 * 400 sec. bin1, B = 10 * 500 sec. bin1.

Pixinsight 1.8, Photoshop.

M 92

M 3

Messier 3 (also known as M3 or NGC 5272) is a globular cluster of stars in the northern constellation of Canes Venatici. It was discovered by Charles Messier on May 3, 1764, and resolved into stars by William Herschel around 1784. Since then, it has become one of the best-studied globular clusters. Identification of the cluster's unusually large variable star population was begun in 1913 by American astronomer Solon Irving Bailey and new variable members continue to be identified up through 2004.

Many amateur astronomers consider it one of the finest northern globular clusters, following only Messier 13. M3 has an apparent magnitude of 6.2, making it a difficult naked eye target even with dark conditions. With a moderate-sized telescope, the cluster is fully defined. It can be a challenge to locate through the technique of star hopping, but can be found by looking almost exactly halfway along an imaginary line connecting the bright star Arcturus to Cor Caroli. Using a telescope with a 25 cm (9.8 in) aperture, the cluster has a bright core with a diameter of about 6 arcminutes and spans a total of 12 arcminutes.

This cluster is one of the largest and brightest, and is made up of around 500,000 stars. It is estimated to be 8 billion years old. It is located at a distance of about 33,900 light-years away from Earth.[citation needed]

RGB = 20 * 300 sec, in the each filters.

Pixinsight 1.8, Lightroom.

M 3