Hydrus is a small constellation in the deep southern sky. It was one of twelve constellations created by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman and it first appeared on a 35-cm (14 in) diameter celestial globe published in late 1597 in Amsterdam by Plancius and Jodocus Hondius. The first depiction of this constellation in a celestial atlas was in Johann Bayer's Uranometria of 1603. The French explorer and astronomer Nicolas Louis de Lacaille charted the brighter stars and gave their Bayer designations in 1756. Its name means "male water snake", as opposed to Hydra, a much larger constellation that represents a female water snake. It remains below the horizon for most Northern Hemisphere observers.
Tucana is a constellation of stars in the southern sky, named after the toucan, a South American bird. It is one of twelve constellations conceived in the late sixteenth century by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman. Tucana first appeared on a 35-centimetre-diameter (14 in) celestial globe published in 1598 in Amsterdam by Plancius and Jodocus Hondius and was depicted in Johann Bayer's star atlas Uranometria of 1603. French explorer and astronomer Nicolas Louis de Lacaille gave its stars Bayer designations in 1756. The constellations Tucana, Grus, Phoenix and Pavo are collectively known as the "Southern Birds".
The Small Magellanic Cloud (SMC), or Nubecula Minor, is a dwarf galaxy near the Milky Way. Classified as a dwarf irregular galaxy, the SMC has a D25 isophotal diameter of about 5.78 kiloparsecs (18,900 light-years), and contains several hundred million stars. It has a total mass of approximately 7 billion solar masses. At a distance of about 200,000 light-years, the SMC is among the nearest intergalactic neighbors of the Milky Way and is one of the most distant objects visible to the naked eye.
Perseus is a constellation in the northern sky, being named after the Greek mythological hero Perseus. It is one of the 48 ancient constellations listed by the 2nd-century astronomer Ptolemy, and among the 88 modern constellations defined by the International Astronomical Union (IAU). It is located near several other constellations named after ancient Greek legends surrounding Perseus, including Andromeda to the west and Cassiopeia to the north. Perseus is also bordered by Aries and Taurus to the south, Auriga to the east, Camelopardalis to the north, and Triangulum to the west. Some star atlases during the early 19th century also depicted Perseus holding the disembodied head of Medusa, whose asterism was named together as Perseus et Caput Medusae; however, this never came into popular usage.
The Tarantula Nebula is a large H II region in the Large Magellanic Cloud (LMC), forming its south-east corner.
R136a1 is one of the most massive and luminous stars known, at 196 M☉ and nearly 4.7 million L☉, and is also one of the hottest, at around 46,000 K. It is a Wolf–Rayet star at the center of R136, the central concentration of stars of the large NGC 2070 open cluster in the Tarantula Nebula in the Large Magellanic Cloud. The cluster can be seen in the far southern celestial hemisphere with binoculars or a small telescope, at magnitude 7.25. R136a1 itself is 100 times fainter than the cluster and can only be resolved using speckle interferometry.
NGC 1806 is a globular cluster located within the Large Magellanic Cloud within the constellation of Dorado, an area of the sky best seen from the Earth's southern hemisphere. It was discovered in 1836 by the British astronomer John Herschel. At an aperture of 50 arcseconds, its apparent V-band magnitude is 11.00, but at this wavelength, it has 0.05 magnitudes of interstellar extinction.
NGC 2257 is a globular cluster that lies on the outskirts of the Large Magellanic Cloud (LMC). It was discovered in 1834 by John Herschel. The compiler of the New General Catalogue, John Louis Emil Dreyer, described this cluster as "faint, considerably large, round, very gradually a little brighter middle, mottled but not resolved, 17.0 seconds of time diameter." At an aperture of 30.5 arcseconds, its apparent V-band magnitude is 12.62, but at this wavelength, it has 0.12 magnitudes of interstellar extinction.
NGC 339 is a globular cluster in the constellation Tucana the Toucan. It is located both visually and physically in the Small Magellanic Cloud, being only about 10,000 ± 12,000 light years closer than the cloud. It is rather prominent, being the brightest cluster in the southern reaches of the cloud. It was discovered by John Herschel on September 18, 1835. It was observed in 2005 by the Hubble Space Telescope. Its apparent V-band magnitude is 12.12, but at this wavelength, it has 0.19 magnitudes of interstellar extinction.
NGC 1783 is a globular cluster within the Dorado constellation and part of the Large Magellanic Cloud, a satellite dwarf galaxy of the Milky Way. At an aperture of 50 arcseconds, its apparent V-band magnitude is 10.39, making it one of the brightest globular clusters in the LMC as viewed from Earth. It was discovered in 1835 by John Herschel. The compiler of the New General Catalogue, John Louis Emil Dreyer, described this cluster as "considerably bright, large, round, very gradually pretty much brighter middle, mottled but not resolved."
AB8, also known as SMC WR8, is a binary star in the Small Magellanic Cloud (SMC). A Wolf-Rayet star and a main sequence companion of spectral type O orbit in a period of 16.638 days. It is one of only nine known WO stars, the only Wolf-Rayet star in the SMC not on the nitrogen sequence, and the only Wolf-Rayet star in the SMC outside the main bar.
NGC 152 is an open cluster in the constellation Tucana. It was discovered by John Herschel on September 20, 1835. It is located within the Small Magellanic Cloud.
NGC 330 is an open cluster in the Small Magellanic Cloud. It is located in the constellation Tucana. It was discovered on 1 August, 1826 by James Dunlop. It was described by Dreyer as "a globular cluster, very bright, small, a little extended, stars from 13th to 15th magnitude." At an aperture of 31.0 arcseconds, the apparent V-band magnitude is 9.60, but at this wavelength, it also has 0.36 magnitudes of interstellar extinction.
NGC 1846 is a globular cluster containing hundreds of thousands of stars in the outer halo of the Large Magellanic Cloud. It was discovered on November 6, 1826 by James Dunlop and is included in the New General Catalogue. At an aperture of 50 arcseconds, its apparent V-band magnitude is 10.68, but at this wavelength, it has 0.07 magnitudes of interstellar extinction.
NGC 411 is a globular cluster located approximately 55,000 pc (180,000 ly) from Earth in the constellation Tucana. It was discovered in 1826 by James Dunlop. It was described by Dreyer as "extremely faint, pretty large, round, gradually very little brighter middle". At a distance of about 180,000 light years (55,000 parsecs), it is located within the Small Magellanic Cloud. It has a mass of about 3.0×104 M☉, and a luminosity of about 8.0×104 L☉.
NGC 416 is a globular cluster located in the constellation Tucana. It was discovered on September 5, 1826, by James Dunlop. It was described by Dreyer as "faint, pretty small, round, gradually brighter middle". At a distance of about 199,000 ± 9,800 ly (61,000 ± 3,000 pc), it is located within the Small Magellanic Cloud. At an aperture of 31 arcseconds, its apparent V-band magnitude is 11.42, but at this wavelength, it has 0.25 magnitudes of interstellar extinction.
NGC 419 is a globular cluster located approximately 57,000 pc (190,000 ly) from Earth in the constellation Tucana. It was discovered on September 2, 1826 by James Dunlop. It was described by Dreyer as "pretty large, pretty bright, round, gradually brighter middle". At a distance of about 186,000 light years, it is located within the Small Magellanic Cloud. At an aperture of 50 arcseconds, its apparent V-band magnitude is 10.30, but at this wavelength, it has 0.15 magnitudes of interstellar extinction.
The Eridanus II Dwarf is a low-surface brightness dwarf galaxy in the constellation Eridanus. Eridanus II was independently discovered by two groups in 2015, using data from the Dark Energy Survey. This galaxy is probably a distant satellite of the Milky Way. Li et al., 2016. Eridanus II contains a centrally located globular cluster; and is the smallest, least luminous galaxy known to contain a globular cluster. Crnojević et al., 2016. Eridanus II is significant, in a general sense, because the widely accepted Lambda CDM cosmology predicts the existence of many more dwarf galaxies than have yet been observed. The search for just such bodies was one of the motivations for the ongoing Dark Energy Survey observations. Eridanus II has special significance because of its apparently stable globular cluster. The stability of this cluster, near the center of such a small, diffuse, galaxy places constraints on the nature of dark matter. Brandt 2016.
NGC 458 is an open cluster located in the constellation Tucana. It was discovered on September 6, 1826, by James Dunlop. It was also observed by John Herschel and DeLisle Stewart. It was described by Dreyer as "pretty faint, large, round, very gradually brighter middle". It was also noted in the second Index Catalogue that it was "probably a cluster, extremely small, close, no nebulosity seen by D.S. ." At an aperture of 31 arcseconds, its apparent V-band magnitude is 11.73, but at this wavelength, it has 0.12 magnitudes of interstellar extinction.
NGC 1978 is an elliptical shaped globular cluster or open cluster in the constellation Dorado. It is located within the Large Magellanic Cloud. It was discovered by James Dunlop on November 6, 1826. At an aperture of 50 arcseconds, its apparent V-band magnitude is 10.20, but at this wavelength, it has 0.16 magnitudes of interstellar extinction. It appears 3.9 arcminutes wide. NGC 1978 has a radial velocity of 293.1 ± 0.9 km/s.
