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. 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. 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 official constellation boundaries, as set by 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.
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. 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. The four main stars—Gamma, Delta, Epsilon and Eta—make up a square in this region of faint stars. Gamma1 and Gamma2 Normae are an optical double and not a true binary star system. Located 129 ± 1 light-years away from Earth. Gamma2 Normae is a yellow giant of spectral type G8III around 2 to 2.5 times as massive as the Sun. It has swollen to a diameter 10 times that of the Sun and shines with 45 times the Sun’s luminosity. Gamma1 Normae is a yellow-white supergiant, located much further away at around 1500 light-years from Earth. Delta Normae is a white, A-class star about 123 light years from Earth. It has an apparent magnitude of 4.73. Epsilon Normae is a spectroscopic binary, with two blue-white main sequence stars of almost equal mass and spectral type (B3V) orbiting each other every 3.26 days. There is a third star separated by 22 arcseconds, which has a magnitude of 7.5 and is likely a smaller B-type main sequence star of spectral type B9V. The system is 530 ± 20 light-years distant from Earth, Eta Normae is a yellow giant of spectral type G8III with an apparent magnitude of 4.65. It shines with a luminosity approximately 66 times that of the Sun.
Four-star systems are known to harbour planets. HD 330075 is a sun-like star around 164 light-years distant that is orbited by a hot Jupiter every 3.4 days. Announced in 2004, it was the first planet discovered by the HARPS spectrograph. HD 148156 is a star 168 ± 7 light-years distant. Slightly larger and hotter than the Sun, it was found to have a roughly Jupiter-size planet with an orbital period of 2.8 years. HD 143361 is a binary star system composed of a sun-like star and a faint red dwarf separated by 30.9 AU. A planet roughly triple the mass of Jupiter orbits the brighter star every 1057± 20 days. HD 142415 is approximately 113 light-years distant and has a Jupiter-sized planet with an orbital period of around 386 days.
Due to its location on the Milky Way, this constellation contains many deep-sky objects such as star clusters, including eight open clusters. NGC 6087 is the brightest of the open clusters in Norma with a magnitude of 5.4. It lies in the south-eastern corner of the constellation between Alpha Centauri and Zeta Arae. Thought to be around 100 million years old, it is about 3300 light-years away and is around 14 light-years in diameter. Its brightest member is the Cepheid variable S Normae. A rich background star field makes it less distinct, though around 36 member stars are visible. Located 0.4° north of Kappa Normae is NGC 6067, which has an integrated magnitude of 5.6 though it is indistinct as it lies in a rich star field. It is thought to be around 102 million years old, and contain 891 solar masses. Two Cepheid variables—QZ Normae and V340 Normae—have been identified as members of the cluster. Fainter open clusters include NGC 6134 with a combined magnitude of 7.2 and located 4000 light-years away from Earth, the spread-out NGC 6167 of magnitude 6.7, NGC 6115 near Gamma Normae, NGC 6031 and NGC 5999. NGC 6152 is also an open star cluster. It was discovered by the English astronomer John Herschel on June 8, 1834. The cluster has an apparent magnitude of 8.1 and is approximately 3,360 light years distant from the solar system. It is 25’ in diameter. Located around 4900 light-years distant is Shapley 1 (or PK 329+02.1), a planetary nebula better known as the Fine-Ring Nebula. Around 8700 years old, it lies about five degrees west-northwest of Gamma1 Normae. Its integrated magnitude is 13.6 and its mean surface brightness is 13.9. The central star is a white dwarf of magnitude 14.03. Mz 1 is a bipolar planetary nebula, thought to be an hourglass shape tilted at an angle to observers on Earth, some 3500 light-years distant. Mz 3—known as the Ant Nebula as it resembles an ant—has a complex appearance, with at least four outflow jets and two large lobes visible. Approximately 200 million light-years from Earth with a redshift of 0.016 is Abell 3627; also called the Norma Cluster, it is one of the most massive galaxy clusters known to exist, at ten times the average cluster mass. Abell 3627 is thus theorized to be the Great Attractor, a massive object that is pulling the Local Group, the Virgo Supercluster, and the Hydra-Centaurus Supercluster towards its location at 600–1000 kilometres per second. Credit: Wikipedia.