The Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph), also known as the Sagittarius Dwarf Elliptical Galaxy, is an elliptical loop-shaped satellite galaxy of the Milky Way. It contains four globular clusters in its main body, with the brightest of them—NGC 6715 (M54)—being known well before the discovery of the galaxy itself in 1994. Sgr dSph is roughly 10,000 light-years in diameter, and is currently about 70,000 light-years from Earth, travelling in a polar orbit at a distance of about 50,000 light-years from the core of the Milky Way. In its looping, spiraling path, it has passed through the plane of the Milky Way several times in the past. In 2018 the Gaia project of the European Space Agency showed that Sgr dSph had caused perturbations in a set of stars near the Milky Way's core, causing unexpected rippling movements of the stars triggered when it moved past the Milky Way between 300 and 900 million years ago.
The Butterfly Cluster is an open cluster of stars in the southern constellation of Scorpius. Its name derives from the vague resemblance of its shape to a butterfly. The Trumpler classification of II 3 r encodes it is rich in stars, ranks II out of IV for disparateness and greatly mixes bright with faint components. It is 3.5° to the northwest of Messier 7, both north of the tail of Scorpius.
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 19 or M19 is a globular cluster in the constellation Ophiuchus. It was discovered by Charles Messier on June 5, 1764 and added to his catalogue of comet-like objects that same year. It was resolved into individual stars by William Herschel in 1784. His son, John Herschel, described it as "a superb cluster resolvable into countless stars". The cluster is located 4.5° WSW of Theta Ophiuchi and is just visible as a fuzzy point of light using 50 mm (2.0 in) binoculars. Using a telescope with a 25.4 cm (10.0 in) aperture, the cluster shows an oval appearance with a 3′ × 4′ core and a 5′ × 7′ halo.
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 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 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 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 52 or M52, also known as NGC 7654, 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.
Messier 67 and sometimes called the King Cobra cluster or the Golden Eye cluster is an open cluster in the southern, equatorial half of Cancer. It was discovered by Johann Gottfried Koehler in 1779. Estimates of its age range between 3.2 and 5 billion years. Distance estimates are likewise varied, but typically are 800–900 parsecs (2,600–2,900 ly). Estimates of 855, 840, and 815 pc were established via binary star modelling and infrared color-magnitude diagram fitting.
Messier 69 or M69, also known NGC 6637, is a globular cluster in the southern constellation of Sagittarius. It can be found 2.5° to the northeast of the star Epsilon Sagittarii and is dimly visible in 50 mm aperture binoculars. The cluster was discovered by Charles Messier on August 31, 1780, the same night he discovered M70. At the time, he was searching for an object described by Nicolas-Louis de Lacaille in 1751–2 and thought he had rediscovered it, but it is unclear if Lacaille actually described M69.
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.
Kappa Crucis is a spectroscopic binary star in the open cluster NGC 4755, which is also known as the Kappa Crucis Cluster or Jewel Box Cluster.
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.
V1073 Scorpii is a variable star in the constellation Scorpius. It has a non-Greek Bayer designation of k Scorpii. The star has a blue-white hue and is visible to the naked eye with an apparent visual magnitude that fluctuates around +4.87. Parallax measurements yield a distance estimate of approximately 2,920 ly (896 pc) from the Sun, and it is drifting further away with a radial velocity of +7 km/s. It has an absolute magnitude of −6.8
DS Crucis is a variable star near the open cluster NGC 4755, which is also known as the Kappa Crucis Cluster or Jewel Box Cluster. It is in the constellation Crux.
DU Crucis is a red supergiant and slow irregular variable star in the open cluster NGC 4755, which is also known as the Kappa (κ) Crucis Cluster or Jewel Box Cluster.
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.
Trumpler 27 is a possible open cluster in the southern constellation Scorpius. If it exists, it is a few thousand light-years away from the Sun, with estimates ranging from 3,900 light-years to 6,800 light-years The name refers to Robert Julius Trumpler's catalog of open clusters, published in 1930.
