Norma

Norma

Constellation
List of stars in Norma
Abbreviation	Nor
Genitive	Normae
Pronunciation	/ˈnɔrmə/, genitive /ˈnɔrmiː/
Symbolism	the Normal
Right ascension	16.05
Declination	−52.01
Area	165 sq. deg. (74th)
Main stars	2
Bayer/Flamsteed stars	13
Stars with known planets	3
Bright stars	0
Nearby stars	0
Brightest star	γ2 Nor (4.0m)
Nearest star	HD 139211 (101 ly)
Messier objects	0
Meteor showers	Gamma Normids
Bordering constellations	Scorpius Lupus Circinus Triangulum Australe Ara
Visible at latitudes between +30° and −90°. Best visible at 21:00 (9 p.m.) during the month of July.

Norma is a small and inconspicuous constellation in the southern hemisphere between Scorpius and Centaurus. 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.

History

As there are no particularly bright stars from Norma southward toward the Pole, there were no constellations placed in this area in Ptolemy's Almagest. However, through the quirks of history, it now features three objects prominent in Euclid's Elements.

Norma was originally known as the Southern Triangle (no relation to Triangulum Australe) or Quadrans Euclidis (Euclid's square). It was given its current name by Nicolas Louis de Lacaille during his stay at the Cape of Good Hope from 1751 to 1752.

Dutch mapmaker Petrus Plancius had explorers Pieter Dirkszoon Keyser and Frederick de Houtman record the positions of the southern stars, and then included them in his 1589 celestial chart. He also created new constellations. One of them was a "Southern Triangle," but although it was a popular idea, there were competing notions as to where it should be located, and it "floated" from map to map: Volans (Plancius' choice), Norma, and Triangulum Australe were all proposed sites. It was Lacaille, in 1763, who fixed it in its present location, but viewed it as a Surveyor's Triangle (essentially an A-Frame with a Plumb-bob attached). He then went on to create two more surveyor's instrument constellations, all contiguous. One was Circinus, a pair of compasses, the other was Norma.

He called it L'Équerre et La Règle (the set square and the ruler) known formally by the Latin, Norma et Regula. While the chart only shows a short line for the figure, Lacaille pictured the ruler running from ε to ι with the right-angled set square (γ, η, and δ) lying next to it. Over time, however, perception of these constellations has changed from a collection of surveyor's tools to a set of geometrically important objects: straightedge, compass, and equilateral triangle.

Thus, oddly, while the name of this constellation has shortened to Norma, in its visualization it is the square that has disappeared and the ruler that remains. Additionally, changes in the boundaries of the constellations since Lacaille’s time have resulted in the removal of a number of stars from Norma, including the 4th magnitude stars that Lacaille designated α and β, which are now known as N and H Scorpii.

Notable features

Stars

The Milky Way passes through Norma.

Norma has no α or β star; its brightest star, γ² Normae, is only of magnitude 4.0. Among the constellation's principal stars are the following:

• γ¹ Nor and γ² Nor comprise an easy optical double. γ² Nor is itself a close optical double (HJ 4841).

• ε Nor: a relatively fixed binary star (HJ 4853). The two components are of magnitude 4.54 and 6.68; the separation is 22" in PA 335°. The fainter component is itself a spectroscopic binary (mag 6.68 and 7.12).

• ι¹ Nor: a multiple star. The AB (mag 5.6 and 5.8) pair comprise a rapid binary with a period of 26.9 years; in 2000 the separation was 0.5" in PA 285°. Component C, of magnitude 8.75, is 11" away in PA 242°; it is not a physical member of the system, being only 55 light-years away, while the AB pair lie at a distance of more than 140 ly.

• μ Nor is suspected of being an Alpha Cygni variable, with a range of 4.87–4.98. It is of spectral type O9.7 Iab.

• R Normae is a Mira variable. Its visual range is 6.5–13.9 and its average period is 507.5 days.

• S Normae is a well-known Cepheid variable with a range of 6.12–6.77 and a period of 9.75411 days. It is located at the centre of the open cluster NGC 6087.

Deep-sky objects

Due to its location on the Milky Way, this constellation contains many deep sky objects, the most notable of which is NGC 6087.

• NGC 6067 is an open cluster, which lies less than 1° north of Kappa Normae. It contains about 100 stars of the tenth magnitude and has an integrated magnitude of 5.6m.

• NGC 6087 is the brightest of the open clusters in Norma; it lies in the southeastern corner of the constellation between α Centauri and ζ Arae. It is about 3500 light-years away and contains about 40 stars of the seventh to the eleventh magnitude. Its brightest member is the Cepheid variable S Normae. It is of magnitude +5.4.

• Sp 1 (or PK 329+02.1) is a planetary nebula better known as the Fine-Ring Nebula. It lies about five degrees west-northwest of γ¹ Nor, though its actual distance has been variously estimated at 1000–4700 ly. Its integrated magnitude is 13.6 and its mean surface brightness is 13.9. The central star is a white dwarf of mag 14.03.

References

• Burnham, Robert Jr. (1966, 1978). Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System, v.2. General Publishing Company, Ltd., Toronto. ISBN 0-486-23568-8. 
• Ian Ridpath and Wil Tirion (2007). Stars and Planets Guide, Collins, London. ISBN 978-0007251209. Princeton University Press, Princeton. ISBN 978-0691135564.

External links

Wikimedia Commons has media related to: Norma

• Yale Bright Star Catalog
• Norma on Robin Gatter's site
• Star Tales – Norma
• Norma on Richard Dibon-Smith's site
• Peoria Astronomical Society: Norma
• The Deep Photographic Guide to the Constellations: Norma

Coordinates: 16^h 03^m 00^s, −52° 00′ 36″