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 23, also known as NGC 6494, is an open cluster of stars in the northwest of the southern constellation of Sagittarius. It was discovered by Charles Messier in 1764. It can be found in good conditions with binoculars or a modestly sized telescope. It is in front of "an extensive gas and dust network", which there may be no inter-association. It is within 5° the sun's position so can be occulted by the moon.
Messier 39 or M39, also known as NGC 7092, is an open cluster of stars in the constellation of Cygnus, positioned two degrees to the south of the star Pi Cygni and around 9° east-northeast of Deneb. The cluster was discovered by Guillaume Le Gentil in 1749, then Charles Messier added it to his catalogue in 1764. When observed in a small telescope at low power the cluster shows around two dozen members but is best observed with binoculars. It has a total integrated magnitude (brightness) of 5.5 and spans an angular diameter of 29 arcminutes – about the size of the full Moon. It is centered about 1,010 light-years away.
Messier 52 or M52, also known as NGC 7654 or the Scorpion Cluster, is an open cluster of stars in the highly northern constellation of Cassiopeia. It was discovered by Charles Messier in 1774. It can be seen from Earth under a good night sky with binoculars. The brightness of the cluster is influenced by extinction, which is stronger in the southern half. Its metallicity is somewhat below that of the Sun, and is estimated to be [Fe/H] = −0.05 ± 0.01.
NGC 381 is an open cluster of stars in the northern constellation of Cassiopeia, located at a distance of approximately 3,120 light-years from the Sun. Credit for the discovery of this cluster was given to Caroline Herschel by her brother William in 1787, although she may never have actually seen it.
NGC 5749 is an open cluster of stars positioned near the southwest border of the southern constellation of Lupus. It is located at a distance of 3,548 light years from the Sun. This is a poorly populated cluster that shows a low level of concentration; the Trumpler class is IV1p. There are 112 stars brighter than magnitude 14.4 within an angular radius of ~15′ of the cluster center, but only about 30% of these are members. NGC 5749 is 27 million years old with a tidal radius of 11.7 light years and a mass of ~21 M☉. Polarization measurements suggest there is a dust cloud within the cluster.
NGC 2374 is an open cluster of stars in the Canis Major constellation. It was discovered on January 31, 1785 by the German-British astronomer William Herschel. This cluster is relatively rich in stars but is scattered across an angular diameter of 19.0′. It has an integrated visual magnitude of 8.0 and can be viewed with a modest amateur telescope. NGC 2374 is located at a distance of approximately 3,950 light-years (1,212 pc) from the Sun.
NGC 637 is an open cluster of stars in the northern constellation of Cassiopeia, positioned about 1.5° to the WNW of the star Epsilon Cassiopeiae. The cluster was discovered on 9 November 1787 by German-born English astronomer William Herschel. It is located in the Perseus Arm of the Milky Way, at a distance of approximately 7.045 kilolight-years from the Sun. The cluster is small but compact, and is readily visible in a small telescope.
NGC 6834 is a young open cluster of stars located about 10,850 light years from the Sun in the constellation Cygnus. It was discovered on July 17, 1784, by Anglo-German astronomer William Herschel. The cluster has a visual magnitude of 7.8, which is dimmed by 2.1 magnitudes due to interstellar dust. Half the cluster members lie within an angular radius of 6′.
NGC 6281 is an open cluster of stars in the constellation Scorpius. It was not included in the Messier or Caldwell catalogues of nebulous objects, but it is the brightest such cluster in the constellation to be left out of both. It is readily observed with the naked eye; it is located about 2° to the east of Mu Scorpii. James Dunlop described the cluster as a "curiously curved line of pretty bright stars, with many stars mixt". John Herschel then described the cluster as both "pretty bright" and "pretty rich".
NGC 2439 is a sparse open cluster of stars in the constellation Puppis. It has an apparent visual magnitude of 6.9, an angular size of 10 arcminutes, and is visible using a small telescope. This is a young cluster with age estimates in the range of 20–300 million years. It has a tidal radius of approximately 82 light years. No chemically peculiar stars have been found.
NGC 2539 is an open cluster in the constellation Puppis, located at the north edge of the constellation. It was discovered by William Herschel on January 31, 1785. It is a moderately rich cluster and with little central concentration, with Trumpler class II1m.
NGC 5460 is an open cluster in the constellation Centaurus. It is a bright but loose cluster of intermediate age located approximately 2,300 light years away from Earth. It is located nearly 2 degrees east-southeast of Zeta Centauri.
NGC 2266 is an open cluster of stars in the constellation of Gemini. It was discovered by German-British astronomer William Herschel on 7 December 1785. This is a relatively dim cluster with an integrated visual magnitude of 9.5 and an angular size of 5.0′. The stellar members can be readily resolved with an amateur telescope. NGC 2266 is located at a distance of 10,603 ly (3,251.0 pc) from the Sun. It is located close to the opposite part of the sky from the Galactic Center, or the anti-center.
NGC 2527 is an open cluster in the constellation Puppis. It was discovered by William Herschel on December 9, 1784. The cluster was also observed by John Herschel on January 7, 1831. He also observed it on February 5, 1837, identifying it as a different object, which was catalogued as NGC 2520. It is a poor cluster and with no central concentration, with Trumpler class III1p.
NGC 7160 is an open cluster in the constellation Cepheus. It was discovered by William Herschel on November 9, 1789. The cluster was also observed by John Herschel on October 7, 1829. It is a poor cluster and with little central concentration, with Trumpler class II3p. It is part of the stellar association Cepheus OB2, located one degree south-southwest of VV Cephei.
NGC 6910 is an open cluster in the constellation Cygnus. It was discovered by William Herschel on October 17, 1786. The cluster was also observed by John Herschel on September 18, 1828. It is a poor cluster with prominent central concentration and Trumpler class I2p. NGC 6910 is the core cluster of the stellar association Cygnus OB9.
NGC 1444 is a small open cluster of stars in the northern constellation of Perseus, about 2-1⁄4° to the northwest of 43 Persei. It has an angular diameter of 4 arcminutes and a brightness of 6.60 in visual magnitude. The cluster has sixty members of seventh magnitude or fainter, and is better appreciated in larger telescopes. NGC 1444 was discovered on 18 December 1788 by the German-British astronomer William Herschel. It is located at a distance of 4,200 light-years from the Sun and is about 7.1 million years old. The cluster has a physical core radius of 1.73 ± 0.42 ly and a tidal radius of 17.4 ± 4.2 ly. The most prominent member is the triple star system Σ446, with a magnitude 6.7 primary. The cluster is a member of the Camelopardalis OB1 association.
NGC 1513 is an open cluster of stars in the northern constellation of Perseus, positioned 2° SSE of the faint star Lambda Persei. The same telescope field contains the clusters NGC 1528 and NGC 1545. NGC 1513 was discovered in 1790 by the German-British astronomer William Herschel. The brightest component star is of magnitude 11, so a medium-sized amateur telescope is needed to observe 20-30 members. With a 12 in (30 cm) aperture telescope, most of the member stars can be resolved. This cluster is located at a distance of 4,824 light-years from the Sun, but is drawing closer with a radial velocity of −14.7 km/s.
