Messier 73. History[edit] M73 was discovered by Charles Messier on October 4, 1780, who originally described the object as a cluster of four stars with some nebulosity. Subsequent observations by John Herschel, however, failed to reveal any nebulosity. Moreover, Herschel noted that the designation of M73 as a cluster was questionable. Nonetheless, Herschel included M73 in his General Catalogue of clusters, nebulae, and galaxies, and John Dreyer included M73 when he compiled the New General Catalogue.[3] Scientific Research: Asterism or Open Cluster? M73 was once treated as a potential sparsely populated open cluster, which consists of stars that are physically associated in space as well as on the sky. In 2000, L. Although M73 was determined to be only a chance alignment of stars, further analysis of asterisms is still important for the identification of sparsely populated open clusters.
Location[edit] The asterism's location in the sky is shown in the following map of the constellation Aquarius: Messier 72. This cluster is visible as a faint nebula in a telescope with a 6 cm (2.4 in) aperture. the surrounding field stars become visible at 15 cm (5.9 in), while 25 cm (9.8 in) is sufficient to resolve the cluster with an angular diameter of 2.5′. At 30 cm (12 in) the core is resolved in a 1.25′ diameter, showing a broad spread with darker regions to the south and east.[9] Based upon a 2011 census of variable stars, Messier 72 is located at a distance of 54.57 ± 1.17 kly (16.73 ± 0.36 kpc) from the Sun.[3] It has an estimated combined mass equal to 168,000[5] times the mass of the Sun and is around 9.5 billion years old. The core region has a density of stars that is radiating 2.26 times the luminosity of the Sun per cubic parsec.[6] There are 43 identified variable stars in the cluster.[3] References[edit] Jump up ^ Shapley, Harlow; Sawyer, Helen B. External links[edit] Coordinates:
Messier 2. Discovery and visibility[edit] M2 was discovered by the French astronomer Jean-Dominique Maraldi in 1746 while observing a comet with Jacques Cassini. Charles Messier rediscovered it in 1760, but thought it a nebula without any stars associated with it. William Herschel, in 1783, was the first to resolve individual stars in the cluster. M2 is, under extremely good conditions, just visible to the naked eye. Binoculars or a small telescope will identify this cluster as non-stellar, while larger telescopes will resolve individual stars, of which the brightest are of apparent magnitude 13.1.
Characteristics[edit] M2 is about 37,500 light-years distant from Earth. M2 contains about 150,000 stars, including 21 known variable stars. References[edit] Jump up ^ Shapley, Harlow; Sawyer, Helen B. External links[edit] Coordinates: 21h 33m 27s, −00° 49′ 24″ Aquarius_IAU. Aquarius (constellation) (Unicode ♒), a representation of water. In the Greek tradition, the constellation became represented as simply a single vase from which a stream poured down to Piscis Austrinus. The name in the Hindu zodiac is likewise kumbha "water-pitcher", showing that the zodiac reached India via Greek intermediaries.
In the first century CE, Ptolemy's Almagest established the common Western depiction of Aquarius. His water jar, an asterism itself, consists of Gamma, Pi, Eta, and Zeta Aquarii; it pours water in a stream of more than 20 stars terminating with Fomalhaut, now assigned solely to Piscis Austrinus. The water bearer's head is represented by 5th magnitude 25 Aquarii while his left shoulder is Beta Aquarii; his right shoulder and forearm are represented by Alpha and Gamma Aquarii respectively. The constellation Aquarius as it can be seen by the naked eye. δ Aquarii, also known as Scheat or Skat, is a blue-white A2 spectral class star of magnitude 3.27 and luminosity of 105 L☉. Aquarius.