Norma is a small constellation in the Southern Celestial Hemisphere between Ara and Lupus, one of twelve drawn up in the 18th century by French astronomer Nicolas-Louis de Lacaille and one of several depicting scientific instruments. Its name is Latin for normal, referring to a right angle, and is variously considered to represent a rule, a carpenter's square, a set square or a level. It remains one of the 88 modern constellations. Four of Norma's brighter stars—Gamma, Delta, Epsilon and Eta—make up a square in the field of faint stars. Gamma2 Normae is the brightest star with an apparent magnitude of 4.0. Mu Normae is one of the most luminous stars known, with a luminosity between a quarter million and one million times that of the Sun. Four star systems are known to harbour planets. The Milky Way, particularly the Norma Arm of the galaxy, passes through Norma, and the constellation contains eight open clusters visible to observers with binoculars. The constellation also hosts Abell 3627, also called the Norma Cluster, one of the most massive galaxy clusters known.
History Norma was introduced in 1751–52 by Nicolas-Louis de Lacaille with the French name l’Équerre et la Règle, "the Square and Rule", after he had observed and catalogued 10,000 southern stars during a two-year stay at the Cape of Good Hope. He devised 14 new constellations in uncharted regions of the Southern Celestial Hemisphere not visible from Europe. All but one honoured instruments that symbolised the Age of Enlightenment. Lacaille portrayed the constellations of Norma, Circinus and Triangulum Australe, respectively, as a set square and ruler, a compass, and a surveyor's level in a set of draughtsman instruments, in his 1756 map of the southern stars. The level was dangling from the apex of a triangle, leading some astronomers to conclude he was renaming l’Équerre et la Règle to "le Niveau", "the level". In any case, the constellation's name had been shortened and Latinised by Lacaille to Norma by 1763.
Characteristics Norma is bordered by Scorpius to the north, Lupus to the northwest, Circinus to the west, Triangulum Australe to the south and Ara to the east. Covering 165.3 square degrees and 0.401% of the night sky, it ranks 74th of the 88 constellations in size. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Nor". The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of ten segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 15h 12m 13.6119s and 16h 36m 08.3235s, while the declination coordinates are between −42.27° and −60.44°. The whole constellation is visible to observers south of latitude 29°N.
Features
Stars
Lacaille charted and designated ten stars with the Bayer designations Alpha through to Mu in 1756. However, his Alpha Normae was transferred into Scorpius and left unnamed by Francis Baily, before being named N Scorpii by Benjamin Apthorp Gould, who felt its brightness warranted recognition. Though Beta Normae was depicted on his star chart, it was inadvertently left out of Lacaille's 1763 catalogue, was likewise transferred to Scorpius by Baily and named H Scorpii by Gould. Norma's brightest star, Gamma2 Normae, is only of magnitude 4.0. Overall, there are 44 stars within the constellation's borders brighter than or equal to apparent magnitude 6.5.
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