Canis Major is a constellation in the southern celestial hemisphere. In the second century, it was included in Ptolemy's 48 constellations, and is counted among the 88 modern constellations. Its name is Latin for "greater dog" in contrast to Canis Minor, the "lesser dog"; both figures are commonly represented as following the constellation of Orion the hunter through the sky. The Milky Way passes through Canis Major and several open clusters lie within its borders, most notably M41.
The Rosette Nebula is an H II region located near one end of a giant molecular cloud in the Monoceros region of the Milky Way Galaxy. The open cluster NGC 2244 is closely associated with the nebulosity, the stars of the cluster having been formed from the nebula's matter.
The Eagle Nebula is a young open cluster of stars in the constellation Serpens, discovered by Jean-Philippe de Cheseaux in 1745–46. Both the "Eagle" and the "Star Queen" refer to visual impressions of the dark silhouette near the center of the nebula, an area made famous as the "Pillars of Creation" imaged by the Hubble Space Telescope. The nebula contains several active star-forming gas and dust regions, including the aforementioned Pillars of Creation. The Eagle Nebula lies in the Sagittarius Arm of the Milky Way.
The Wild Duck Cluster is an open cluster of stars in the constellation Scutum. It was discovered by Gottfried Kirch in 1681. Charles Messier included it in his catalogue of diffuse objects in 1764. Its popular name derives from the brighter stars forming a triangle which could resemble a flying flock of ducks. The cluster is located just to the east of the Scutum Star Cloud midpoint.
Messier 21 or M21, also designated NGC 6531 or Webb's Cross, is an open cluster of stars located to the north-east of Sagittarius in the night sky, close to the Messier objects M20 to M25. It was discovered and catalogued by Charles Messier on June 5, 1764. This cluster is relatively young and tightly packed. A few blue giant stars have been identified in the cluster, but Messier 21 is composed mainly of small dim stars. With a magnitude of 6.5, M21 is not visible to the naked eye; however, with the smallest binoculars it can be easily spotted on a dark night. The cluster is positioned near the Trifid nebula, but is not associated with that nebulosity. It forms part of the Sagittarius OB1 association.
Messier 18 or M18, also designated NGC 6613, is an open cluster of stars in the constellation Sagittarius. It was discovered by Charles Messier in 1764 and included in his list of comet-like objects. From the perspective of Earth, M18 is situated between the Omega Nebula (M17) and the Small Sagittarius Star Cloud (M24).
Messier 37 is the brightest and richest open cluster in the constellation Auriga. It was discovered by the Italian astronomer Giovanni Battista Hodierna before 1654. M37 was missed by French astronomer Guillaume Le Gentil when he rediscovered M36 and M38 in 1749. French astronomer Charles Messier independently rediscovered M37 in September 1764 but all three of these clusters were recorded by Hodierna. It is classified as Trumpler type I,1,r or I,2,r.
Messier 46 or M46, also known as NGC 2437, is an open cluster of stars in the slightly southern constellation of Puppis. It was discovered by Charles Messier in 1771. Dreyer described it as "very bright, very rich, very large." It is about 5,000 light-years away. There are an estimated 500 stars in the cluster with a combined mass of 453 M☉, and it is thought to be a mid-range estimate of 251.2 million years old.
The Owl Nebula is a starburst ("planetary") nebula approximately 2,030 light years away in the northern constellation Ursa Major. The estimated age of the Owl Nebula is about 8,000 years. It is approximately circular in cross-section with faint internal structure. It was formed from the outflow of material from the stellar wind of the central star as it evolved along the asymptotic giant branch. The nebula is arranged in three concentric shells/envelopes, with the outermost shell being about 20–30% larger than the inner shell. A mildly owl-like appearance of the nebula is the result of an inner shell that is not circularly symmetric, but instead forms a barrel-like structure aligned at an angle of 45° to the line of sight.
NGC 6822 is a barred irregular galaxy approximately 1.6 million light-years away in the constellation Sagittarius. Part of the Local Group of galaxies, it was discovered by E. E. Barnard in 1884, with a six-inch refractor telescope. It is the closest non-satellite galaxy to the Milky Way, but lies just outside its virial radius. It is similar in structure and composition to the Small Magellanic Cloud. It is about 7,000 light-years in diameter.
Tau Canis Majoris is a multiple star system in the constellation Canis Major. It is approximately 5,000 light years distant from Earth and is the brightest member of the open cluster NGC 2362.
NGC 7380 is a young open cluster of stars in the northern circumpolar constellation of Cepheus, discovered by Caroline Herschel in 1787. The surrounding emission nebulosity is known colloquially as the Wizard Nebula, which spans an angle of 25′. German-born astronomer William Herschel included his sister's discovery in his catalog, and labelled it H VIII.77. The nebula is known as S 142 in the 1959 Sharpless catalog (Sh2-142). It is extremely difficult to observe visually, usually requiring very dark skies and an O-III filter. The NGC 7380 complex is located at a distance of approximately 8.5 kilolight-years from the Sun, in the Perseus Arm of the Milky Way.
NGC 2547 is a southern open cluster in Vela, discovered by Nicolas Louis de Lacaille in 1751 from South Africa. The star cluster is young with an age of 20-30 million years.
NGC 6334, colloquially known as the Cat's Paw Nebula, Bear Claw Nebula, or Gum 64, is an emission nebula and star-forming region located in the constellation Scorpius. NGC 6334 was discovered by astronomer John Herschel in 1837, who observed it from the Cape of Good Hope in South Africa. The nebula is located in the Carina–Sagittarius Arm of the Milky Way, at a distance of approximately 5.5 kilolight-years from the Sun.
NGC 6530 is a young open cluster of stars in the southern constellation of Sagittarius, located some 4,300 light years from the Sun. It exists within the H II region known as the Lagoon Nebula, or Messier 8, and spans an angular diameter of 14.0′. The nebulosity was first discovered by G. B. Hodierna prior to 1654, then re-discovered by J. Flamsteed circa 1680. It was P. Loys who classified it as a cluster in 1746, as he could only resolve stars. The following year, G. Le Gentil determined it was both a nebula and a cluster.
IC 5146 is a reflection/emission nebula and Caldwell object in the constellation Cygnus. The NGC description refers to IC 5146 as a cluster of 9.5 mag stars involved in a bright and dark nebula. The cluster is also known as Collinder 470. It shines at magnitude +10.0/+9.3/+7.2. Its celestial coordinates are RA 21h 53.5m, dec +47° 16′. It is located near the naked-eye star Pi Cygni, the open cluster NGC 7209 in Lacerta, and the bright open cluster M39. The cluster is about 4,000 ly away, and the central star that lights it formed about 100,000 years ago; the nebula is about 12 arcmins across, which is equivalent to a span of 15 light years.
NGC 2281 is an open cluster of stars in the northern constellation of Auriga. It was discovered by English astronomer William Herschel on March 4, 1788 and described as a, "cluster of coarsely scattered pretty [bright] stars, pretty rich". The Trumpler class for NGC 2281 is I3p, indicating a poor (p) but compact (I) grouping with a wide range of brightness (3). It is located at a distance of approximately 1,720 ly from the Sun and is 630–661 million years old.
VY Canis Majoris is an extreme oxygen-rich (O-rich) red hypergiant (RHG) or red supergiant (RSG) and pulsating variable star 1.2 kiloparsecs from the Solar System in the slightly southern constellation of Canis Major. It is one of the largest known stars, one of the most luminous and massive red supergiants, and one of the most luminous stars in the Milky Way.
NGC 2232 is a bright open star cluster in the equatorial constellation of Monoceros, centered on the star 10 Monocerotis. It is located in the Gould Belt close to the Orion Nebula cluster, at a mean distance of 1,060 ly from the Sun. The average radial velocity of the cluster members is 26.6±0.77 km/s. This is one of the nearest open clusters to the Sun, which makes it a potentially useful target for studying young stars and their transition to the main sequence.
NGC 6604 is a young open cluster of stars in the equatorial constellation of Serpens, positioned about 1.5° north of the Eagle Nebula. The cluster was discovered by William Herschel on July 15, 1784. It is located at a distance of 4,580 light years from the Sun, about 210 ly (65 pc) above the galactic plane. NGC 6604 forms the densest part of the Ser OB2 association of co-moving stars.
