47 Tucanae, or 47 Tuc (also designated as NGC 104 and Caldwell 106) is a globular cluster located in the constellation Tucana. It is about away from Earth, and 120 light years in diameter. 47 Tuc can be seen with the naked eye, with an apparent magnitude of 4.1. It appears about 44 arcminutes across including its far outreaches. Due to its far southern location, 18° from the south celestial pole, it was not catalogued by European astronomers until the 1750s, when the cluster was first identified by Nicolas-Louis de Lacaille from South Africa. 47 Tucanae is the second brightest globular cluster after Omega Centauri, and telescopically reveals about ten thousand stars, many appearing within a small dense central core. The cluster may contain an intermediate-mass black hole. Early history The cluster was recorded in 1751-2 by Nicolas-Louis de Lacaille, who initially thought it was the nucleus of a bright comet. Lacaille then listed it as "Lac I-1", the first object listed in his deep-sky catalogue. The number "47" was assigned in Allgemeine Beschreibung und Nachweisung der Gestirne nebst Verzeichniss ("General description and verification of the stars and indexes"), compiled by Johann Elert Bode and published in Berlin in 1801. Bode did not observe this cluster himself, but had reordered Lacaille's catalogued stars by constellation in order of Right Ascension. In the 19th century, Benjamin Apthorp Gould assigned the Greek letter ξ (Xi) to the cluster to designate it ξ Tucanae, but this was not widely adopted and it is almost universally referred to as 47 Tucanae. Characteristics 47 Tucanae is the second brightest globular cluster in the sky (after Omega Centauri), and is noted for having a small very bright and dense core. It is one of the most massive globular clusters in the Galaxy, containing millions of stars. The cluster appears roughly the size of the full moon in the sky under ideal conditions. Though it appears adjacent to the Small Magellanic Cloud, the latter is some distant, being over fifteen times farther than 47 Tuc. A blue giant star with a spectral class of B8III is the brightest star in visible and ultraviolet light, with a luminosity of about 1,100 times that of the Sun, and is aptly known as the "Bright Star". It is a post-AGB star, having passed the asymptotic giant branch phase of its life, and is currently fusing helium. It has an effective