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 25, also known as IC 4725, is an open cluster of stars in the southern constellation of Sagittarius. The first recorded observation of this cluster was made by Philippe Loys de Chéseaux in 1745 and it was included in Charles Messier's list of nebulous objects in 1764. The cluster is located near some obscuring features, with a dark lane passing near the center.
Messier 26, also known as NGC 6694, is an open cluster of stars in the southern constellation of Scutum. It was discovered by Charles Messier in 1764. This 8th magnitude cluster is a challenge to find in ideal skies with typical binoculars, where it can be, with any modern minimum 3-inch (76 mm) aperture device. It is south-southwest of the open cluster Messier 11 and is 14′ across. About 25 stars are visible in a telescope with a 150–200 mm (6–8 in) aperture.
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 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 50 or M 50, also known as NGC 2323, is an open cluster of stars in the constellation Monoceros. It was recorded by G. D. Cassini before 1711 and independently discovered by Charles Messier in 1772 while observing Biela's Comet. It is sometimes described as a 'heart-shaped' figure or a blunt arrowhead.
Messier 93 or M93, also known as NGC 2447, is an open cluster in the modestly southern constellation Puppis, the imagined poop deck of the legendary Argo.
NGC 7789 is an open cluster in Cassiopeia that was discovered by Caroline Herschel in 1783. Her brother William Herschel included it in his catalog as H VI.30. This cluster is also known as the "White Rose" Cluster or "Caroline's Rose" Cluster because when seen visually, the loops of stars and dark lanes look like the swirling pattern of rose petals as seen from above.
NGC 6738 is an astronomical feature that is catalogued as an NGC object. Although listed as an open cluster in some astronomical databases, it may be merely an asterism; a 2003 paper in the journal Astronomy and Astrophysics describes it as being an "apparent concentration of a few bright stars on patchy background absorption".
NGC 6200 is an open cluster in the constellation Ara, lying close to the galactic equator. It contains one β Cephei variable.
IC 4651 is an open cluster of stars located about 2,900 light years distant in the constellation Ara. It was first catalogued by John Louis Emil Dreyer in his 1895 version of the Index Catalogue. This is an intermediate age cluster that is 1.2 ± 0.2 billion years old. Compared to the Sun, the members of this cluster have a higher abundance of the chemical elements other than hydrogen and helium. The combined mass of the active stars in this cluster is about 630 times the mass of the Sun.
NGC 2506 is a mildly-elongated open cluster of stars in the equatorial constellation of Monoceros, located at a distance of 12.7 kly from the Sun near the Galactic anti-center. It was discovered by William Herschel in 1791. The cluster lies around 10,000 ly from the Galactic Center and about 1,600 ly above the Galactic plane. It is of intermediate age, estimated at around two billion years. The cluster has an angular radius of 12′ and a core radius of 4.8′.
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 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 433 is an open cluster in the northern constellation of Cassiopeia, located at a distance of 6,500 light years from the Sun. It was discovered on September 29, 1829, by John Herschel, and was described by John Dreyer as "cluster, small, a little compressed." The cluster is considered on the poor side, with only 12 stars above magnitude 16. It has a linear diameter of 26.3 ly, with around 479 times the mass of the Sun and an age of 65 million years.
NGC 4103 is an open cluster in the constellation Crux. It was discovered by James Dunlop in 1826. It is located approximately 5,000 light years away from Earth, in the Carina-Sagittarius arm.
NGC 2202 is an open cluster in the constellation Orion. The object was discovered in 1825 by the German-Russian astronomer Friedrich Georg Wilhelm von Struve.
