The Phaenomena of Aratus was a popular description of the constellations; it dates to around 275 B.C, and is the earliest surviving discussion of the ancient Greek constellations.5 Its popularity served to freeze the development of the constellations as well as to define the basic properties of the group. The text is largely a version of an earlier (now lost) book of the same name by Eudoxus from around 366 B.C., with substantial further fragments from the work by Eudoxus appearing in the only surviving work of Hipparchus (his Commentary). The Phaenomena gives descriptions of the constellation figures and also tells how these figures relate to the various circles on the sky.
A detailed comparison with the Farnese Atlas shows many differences:
(1) Aratus stated the summer solstice to be at the start of Leo, whereas the statue shows it to be near the head of Pollux with the entire constellation of Cancer between.
(2) The human part of the Centaur is said to be under Scorpius, whereas the statue places it under Virgo, with the entire constellation of Libra between.
(3) Eridanus is said to stop at the neck of Cetus while the stars under Lepus are said to be nameless, whereas the Farnese Atlas shows Eridanus as extending all the way through Columba over to the feet of Canis Major.
(4) Aratus says that Auriga has the Goat and Kids, whereas the globe in Naples shows the Charioteer instead to be holding a whip.
(5) Serpens is said to encircle the waist of Ophiucus, contrary to what is seen on the statue.
(6) The constellation of Libra is depicted as a balance on the globe, but Aratus simply calls it “The Claws”.
(7) The knees of the Charioteer are said to be on the Tropic of Cancer, whereas the globe shows even his feet to be north of the tropic.
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The left shoulder and shin of Perseus are said to be on the Tropic of Cancer, whereas on the statue all of Perseus is north of the tropic.
(9) The head and neck of Cygnus are said to be on the Tropic of Cancer, whereas the sculptor depicts the constellation with the beak tip touching the tropic.
(10) Ophiucus’s shoulders are said to be along the tropic, whereas the globe shows the top of his head to be there.
(11) The knees of Ophiucus are not on the equator as in Aratus, but are depicted as being substantially south of the equator.
(12) The belt of Cepheus is said by Aratus to be on the Arctic Circle, whereas the Atlas has the neck of Cepheus so drawn. There are many further discrepancies for which the case is less clear, for example Aratus says that the head of Draco is on the Arctic Circle and that Crater and Corvus are on the equator, while the globe shows the head only as being near the Arctic Circle and the raven and cup as only tangent to the equator.
