Corona Australis

Authors: Susanne M Hoffmann, Youla Azkarrula

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CrA star chart (IAU and Sky & Telescope magazine, Roger Sinnott & Rick Fienberg).

One of the 88 IAU constellations. The constellation was invented in the first century CE.

Etymology and History

Origin of Constellation

The name ‘Wreath’ for this group of stars has been reliably documented since the 1st century by Geminos. In mathematical astronomy, this constellation first appears in the Almagest; Hipparchus does not mention it. The almost closed ring of stars of approximately equal brightness is mentioned without a name by all earlier authors.

Aratos describes the group as ‘arranged in a ring’. Eratosthenes calls it ‘seven stars of the ship below his [Sagittarius's] lower leg’. This clearly does not refer to the Argo, but to another ship. It is interesting to note in this context that the stars of Corona Australis denote a river boat in Babylonian uranography.

It is quite possible, although not certain, that Eratosthenes' text proves a cultural transfer: In the 3rd century BCE, the Syrian wars raged between the Ptolemies, who ruled Egypt, and the Seleucids, who ruled Mesopotamia. In the last years of Eratosthenes' life and work, there had been a period of peace that made the 2nd century BCE, until the Parthian Wars, an extraordinary heyday of scientific exchange between Babylon and Alexandria. Eratosthenes thus brings together Mesopotamian and newly developed Greek culture.

Modern literature sometimes claims that Hyginus made a possible star prophecy: he tells of a myrtle wreath in memory of the deceased mother of the god Dionysus. However, it is unclear whether he is referring to Corona Borealis or Australis. If Hyginus, the librarian of Augustus, invented the constellation ‘Southern Crown’, there could be a connection to the emperor and his laurel wreath.

It is astonishing that the Southern Crown is depicted on the Farnese Globe. The globe is dated to the 2nd century CE, i.e. the time of Ptolemy. Since the figures are depicted in the Greek style, the globe is considered to be a copy of a Greek original from the BCE era. However, since this star group was not referred to as a wreath until the 1st century CE, the sculptor must have reworked this star figure in a contemporary style. It looks less like a Caesar's crown than a bridal wreath.

Almagest

id	Greek (Heiberg 1898)	English (Toomer 1984)	ident.
	Στεφάνου νοτίου ἀστερισμός	Constellation of the Southern Crown
1	τῆς νοτίου περιφερείας ὁ προηγούμενος ἐκτός	The most advanced ofthe stars on thc southern rim, outside {the crown}	alf Tel
2	ὁ ἐπόμενος αὐτῶν ἐπὶ τοῦ Στεφάνου	The star to the rear of this, on the crown	eta1, eta2 CrA
3	ὁ τούτο ἐπόμενος	The one to the rear of this	HR 7122
4	ὁ ἔτι τούτῳ ἐπόμενος	The one to the rear again of this	zet CrA
5	ὁ μετὰ τοῦτου πρὸ τοῦ γουατίου τοῦ Τοξότου	The one after this, before the knee of Sagittarius	del CrA
6	ὁ μετὰ τοῦτον καὶ βορειότερος τοῦ ἐν τῷ γόνατι λαμπροῦ	The one after this, which is north of the bright star in the knee [of Sagittarius]	bet CrA
7	ὁ τούτου βορειότερος	The star to the north of this	alf CrA
8	ὁ ἔπὶ τούτου βορειότερος	The one to the north again of this	gam CrA
9	τῶν μετὰ τοῦτον προηγουμένωυ β’ ἐν τῇ βορείῳ περιφερείᾳ ὁ ἐπόμενος	The rearmost of the 2 stars after this, in advance, in the northern rim	eps CrA
10	ὁ προηγούμενος τῶν β’ ἀμαυρῶν	The more advanced of these 2 faint stars	HR 7129
11	ὁ τούτου προηγούμενος ἱκανόν	The star quite some distance in advance of this	lam CrA
12	ὁ ἔτι τούτου προηχούμευος	The one in advance again of this	HR 6942
13	ὁ λοιπὸς καὶ νοτιώτερος τοῦ προειρημένου	The last one, which is south of the aforemmtioned star	tet CrA
all	ἀστέρες φ, ὥν δ’ μεγέθους ἐ, εξ. ϛ β	[13 stars, 5 of the fourth magnitude, 6 of the fifth, 2 of the sixth]

Convex Hull for the stars inside Stephanos Notios (CC BY Youla Azkarrula).

Stars within the Constellation Area

id	Label	IAU design.	description	Vmag
1	Meridiana	HIP 94114	Constellation lines (Vertex)	4.087
2	β Coronae Australis	HIP 94160	Constellation lines (Vertex)	4.095
3	γ 1 Coronae Australis	HIP 93825	Constellation lines (Vertex)	4.21
4	δ Coronae Australis	HIP 94005	Constellation lines (Vertex)	4.571
5	θ Coronae Australis	HIP 90982	Constellation lines (Vertex)	4.614
6	ζ Coronae Australis	HIP 93542	Constellation lines (Vertex)	4.725
7	ϵ Coronae Australis	HIP 93174	Constellation lines (Vertex)	4.85
8	λ Coronae Australis	HIP 91875	Constellation lines (Vertex)	5.111
9	-	HIP 90887	Constellation lines (Vertex)	5.155
10	μ Coronae Australis	HIP 92226	Inside the hull	5.217
11	-	HIP 92953	Constellation lines	5.346
12	V686 CrA	HIP 92989	Constellation lines	5.38
13	-	HIP 91989	Inside the hull	5.439
14	η 1 Coronae Australis	HIP 92308	Constellation lines (Vertex)	5.456
15	η 2 Coronae Australis	HIP 92382	Constellation lines	5.587
16	V701 CrA	HIP 93552	Inside the hull	5.716
17	-	HIP 93858	Inside the hull	6.16
18	-	HIP 93470	Inside the hull	6.209
19	-	HIP 90936	Inside the hull	6.217
20	-	HIP 93074	Inside the hull	6.284
21	-	HIP 92608	Inside the hull	6.45
22	-	HIP 92866	Inside the hull	6.47
23	-	HIP 92487	Inside the hull	6.49
24	-	HIP 93209	Inside the hull	6.497

Transfer and Transformation of the Constellation

• 
  CrA in Fortin's Atlas Céleste, 3rd edition (1795).

Mythology

Greek

Eratosthenes does not recount any myth about the river boat on which the archer stands, nor does Geminos give any reasons for the definition of the constellation. It is unclear where the inspiration came from to describe the group as a wreath. However, the Egyptianised style of the Dendera zodiac shows the centaur-like archer on small boats beneath his hooves. This is not surprising in Egypt, where for thousands of years the stars were imagined to glide silently across the sky on barges.

References

• References (general)

• References (ancient Greco-Roman)
• References (medieval)