astronomy

Cygnus constellation

  • October 15, 2017

Cygnus is a northern constellation lying on the plane of the Milky Way, deriving its name from the Latinized Greek word for swan. The swan is one of the most recognizable constellations of the northern summer and autumn, and it features a prominent asterism known as the Northern Cross (in contrast to the Southern Cross). Cygnus was among the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations.

Cygnus contains Deneb, one of the brightest stars in the night sky and one corner of the Summer Triangle, as well as some notable X-ray sources and the giant stellar association of Cygnus OB2. Cygnus is also known as the Northern Cross. Deneb is the tail star in the constellation and is the Arabic word for tail. One of the stars of this association, NML Cygni, is one of the largest stars currently known. The constellation is also home to Cygnus X-1, a distant X-ray binary containing a supergiant and unseen massive companion that was the first object widely held to be a black hole. Many star systems in Cygnus have known planets as a result of the Kepler Mission observing one patch of the sky, an area around Cygnus. In addition, most of the eastern part of Cygnus is dominated by the Hercules–Corona Borealis Great Wall, a giant galaxy filament that is the largest known structure in the observable universe, covering most of the northern sky.

 

Cygnus constellation

  • October 14, 2017

Cygnus is a prominent constellation in the northern sky. Its name means “the swan” in Latin, and it is also known as the Swan constellation.

Cygnus is associated with the myth of Zeus and Leda in Greek mythology. The constellation is easy to find in the sky as it features a well-known asterism known as the Northern Cross. Cygnus was first catalogued the by Greek astronomer Ptolemy in the 2nd century.

Notable objects in the constellation include Cygnus X-1, a famous x-ray source, the bright stars Deneb and Albireo, the Fireworks Galaxy (NGC 6946), and several well-known nebulae: the Pelican Nebula (IC 5070), the North America Nebula (NGC 7000), the Crescent Nebula (NGC 6888), and the Veil Nebula (NGC 6960, 6962, 6979, 6992, and 6995).

Cygnus is the 16th largest constellation in the night sky, occupying an area of 804 square degrees. It lies in the fourth quadrant of the northern hemisphere (NQ4) and can be seen at latitudes between +90° and -40°. The neighboring constellations are Cepheus, Draco, Lacerta, Lyra, Pegasus, and Vulpecula.

Cygnus belongs to the Hercules family of constellations, along with Aquila, Ara, Centaurus, Corona Australis, Corvus, Crater, Crux, Hercules, Hydra, Lupus, Lyra, Ophiuchus, Sagitta, Scutum, Sextans, Serpens, Triangulum Australe, and Vulpecula.

Cygnus has 10 stars with known planets and contains two Messier objects: Messier 29 (NGC 6913) and Messier 39 (NGC 7092). The brightest star in the constellation is Deneb, Alpha Cygni, which is also the 19th brightest star in the sky, with an apparent magnitude of 1.25. There are two meteor showers associated with the constellation: the October Cygnids and the Kappa Cygnids.

 

M13 Globular cluster

  • June 5, 2017

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.[8] 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 22,200 light-years away from Earth.

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. While the cluster will move through space during the transit time, the proper motion is small enough that the cluster will only move 24 light years, only a fraction of the diameter of the cluster. Thus, the message will still arrive near the center of the cluster.

 

NGC 884

  • April 16, 2017

NGC 884 is an open cluster located 7600 light years away in the constellation of Perseus. It is the easternmost of the Double Cluster with NGC 869. NGC 869 and 884 are often designated h and χ Persei, respectively. The cluster is most likely around 12.5 million years old. Located in the Perseus OB1 association, both clusters are located physically close to one another, only a few hundred light years apart. The clusters were first recorded by Hipparchus, but have likely been known since antiquity.

The Double Cluster is a favorite of amateur astronomers. These bright clusters are often photographed or observed with small telescopes. Easy to find, the clusters are visible with the unaided eye between the constellations of Perseus and Cassiopeia as a brighter patch in the winter Milky Way. The Double Cluster was also included in the Caldwell catalogue, a catalogue of astronomical objects for amateur observation.

In small telescopes the cluster appears as a beautiful assemblage of bright stars located in a rich star field. Dominated by bright blue stars the cluster also hosts a few orange stars that add to the visual interest. Both clusters together offer a spectacular low magnification view.