Sagittarius is depicted in the sky as a centaur, with the body and four legs of a horse but the upper torso of a man. He is shown wearing a cloak and drawing a bow, aimed in the direction of the neighbouring Scorpion. Aratus spoke of the Bow, Toxon (Τόξον), and the Archer, Toxotes (Τοξότης), as though they were separate constellations. Most likely this is because the stars of the bow and arrow are the most distinctive part of the figure, forming the asterism we now know as the Teapot. Sagittarius is sometimes misidentified as Chiron. But Chiron is in fact represented by the other celestial centaur, the constellation Centaurus.
Sagittarius, the centaur-like archer, shown drawing his bow in the
Uranographia of Johann Bode (1801).
Sagittarius is a constellation of Sumerian origin, subsequently adopted by the Greeks, and this helps explain the confusion over its identity. Eratosthenes doubted that this constellation was a centaur, giving as one of his reasons the fact that centaurs did not use bows. Instead, Eratosthenes described Sagittarius as a two-footed creature with the tail of a satyr. He said that this figure was Crotus, son of Eupheme, the nurse to the Muses, who were nine daughters of Zeus. According to the Roman mythographer Hyginus, the father of Crotus was Pan, which confirms the view of Eratosthenes that he should be depicted as a satyr rather than a centaur.
Crotus invented archery and often went hunting on horseback. He lived on Mount Helicon among the Muses, who enjoyed his company. They sang for him, and he applauded them loudly. The Muses requested that Zeus place him in the sky, where he is seen demonstrating the art of archery. By his forefeet is a circle of stars that Hyginus said was a wreath ‘thrown off as by one at play’. This circlet of stars is the constellation Corona Australis.
Stars of Sagittarius
Alpha Sagittarii is alternatively called Rukbat or Alrami, both from the Arabic rukbat al-rami, ‘knee of the archer’. Beta Sagittarii is called Arkab, from the Arabic name meaning ‘the archer’s Achilles tendon’. Gamma Sagittarii is Alnasl, from the Arabic meaning ‘the point’, referring to the tip of the archer’s arrow.
Delta, Epsilon and Lambda Sagittarii are respectively called Kaus Media, Kaus Australis and Kaus Borealis. The word Kaus comes from the Arabic al-qaus, ‘the bow’, while the suffixes are Latin words signifying the middle, southern and northern parts of the bow. Zeta Sagittarii is Ascella, a Latin word meaning ‘armpit’. All these names closely follow the descriptions of the stars’ positions given by Ptolemy in his Almagest.
Last, but not least, is Sigma Sagittarii, called Nunki. This name was applied relatively recently by navigators, but it was borrowed from a list of Babylonian star names. The Babylonian name NUN-KI was given to a group of stars representing their sacred city of Eridu on the Euphrates. The name has now been applied exclusively to Sigma Sagittarii, and is reputed to be the oldest star name in use.
Sagittarius contains a rich part of the Milky Way, lying towards the centre of our Galaxy. The exact centre of the Galaxy is believed to be marked by a radio-emitting source that astronomers call Sagittarius A. There are many notable objects in Sagittarius, including the Lagoon Nebula and the Trifid Nebula, two clouds of gas lit up by stars inside them.
Among present-day astronomers, the shape outlined by the eight main stars of Sagittarius (Gamma, Delta, Epsilon, Lambda, Phi, Sigma, Tau and Zeta) is popularly known as the Teapot. A subset of these – Lambda, Phi, Sigma, Tau and Zeta – form a ladle shape called the Milk Dipper, fittingly placed in a rich area of the Milky Way. Ancient Chinese astronomers also imagined a dipper among these same stars (see below).
Sagittarius contained two ancient Chinese constellations after which the seventh and eighth lunar mansions were named: Ji and Dou. Ji (‘winnowing basket’) consisted of four stars – Gamma, Delta, Epsilon and Eta Sagittarii – and represented a basket used for separating rice grains from chaff by shaking it in the air. The chaff, blown away by the breeze, is represented by a single star nearby called Kang, although opinions differ as to whether Kang lay in Sagittarius, Scorpius or even Ophiuchus. A related constellation was Chu, the pestle, to the south of Ji in Ara, for pounding the rice to remove the husks.
Dou (‘dipper’, also known as Nandou, ‘southern dipper’) was formed by Mu, Lambda, Phi, Sigma, Tau and Zeta Sagittarii. These same stars, bar Mu, form the present-day asterism called the Milk Dipper. In a Chinese proverb, the southern dipper marks life while the northern dipper (Beidou, our Big Dipper in Ursa Major) marks death. A single star nearby, probably 5th-magnitude HR 7029, was Nongzhangren, an old farmer, perhaps measuring out grain with the dipper and using the winnowing basket.
To the north of Dou, the arc formed by Upsilon, Rho, 43, Pi, Omicron and Xi Sagittarii was known as Jian, representing a flag or banner, perhaps at a city gate. Next to this was Tianji, ‘celestial cock’, formed by 55 and 56 Sagittarii; the bird represented by this constellation was said to be in charge of time, because it was the first to crow at dawn and all others followed it.
South of Tianji were two canine-related constellations. Gouguo consisted of Omega, 59, 60 and 62 Sagittarii. The name Gouguo is translated as ‘territory of dogs’ or ‘dog kingdom’; it could represent a nation that appears in a Chinese fable or it may simply be an area for dogs around a farm. Next to it was Gou, formed by 52 and Chi-1 Sagittarii, representing a guard dog.
In southern Sagittarius, ten stars probably including Alpha and Beta formed Tianyuan, representing a body of water such as a lake or sea. it was said to govern the irrigation of fields. Some faint stars in Sagittarius on the border with Ophiuchus, identities uncertain, formed part of Tianyue. Lying exactly on the ecliptic, Tianyue represented a lock or keyhole through which the Sun had to pass every year. It lay directly opposite in the sky from Tianguan, a gate on the ecliptic in Taurus.
© Ian Ridpath. All rights reserved