Aries

The Golden Fleece saved Phrixus and Helle, the children of Athamas, from being sacrificed. The ram was later the object of the quest of Jason and the Argonauts. In the Egyptian myth, the constellation was associated with god Amon.

Taurus

The form that Zeus took when he carried off the Phoenician maiden Europa, the brother of Cadmus.

Gemini

The Spartan heroes known as the Dioscuri were the twin sons of Zeus and Leda, and brothers of Helen of Troy. The brothers were named Castor and Polydeuces (Pollux). See the Dioscuri. However the constellation has also been associated with Romulus and Remus, the sons of the war-god Mars.

Cancer

The giant crab that Hera sent against Heracles (Hercules), during his 2nd labour when the hero had to kill the Hydra. Hera immortalised the crab as a constellation Cancer, after Heracles had killed it.

Leo

This constellation was said to be the Nemean Lion, another beast that Heracles (Hercules) had killed, in his 1st labour.

Virgo

This was probably Erigone, the daughter of Icarius (Boötes), and the owner of the dog Maera (the constellation of Canis Minor or the star Sirius). Dionysus immortalised her, her father and the hound. (See Maera for the story in Mythical Creatures.)

Others say the Virgin was Parthenos, the daughter of Apollo and Chrysothemis. Other candidates were another Erigone, the daughter of Aegisthus and Clytemnestra, or Dike (Justice), or Tyche (Fortune).

Libra

Libra is supposed to represent Astraea, the Roman goddess of divine justice. Or this scale could be Scale of Fates, where Jupiter measured the lives between two people, to see who was doomed to die, such as between Achilles and Hector.

Scorpio

According to Hesiod's Astronomy, Gaea (Earth) sent the giant scorpion to kill Orion, though the more popular myth says that Orion was killed by Artemis, either deliberate or an accident.

Sagittarius

This constellation was Crotus, the son of Pan and Eupheme, who was the nurse of the Muses. Zeus immortalised him as the constellation Sagittarius by the request of the Muses.

Capricorn

A goat-like being named Aegipan. This may be another name for Pan, or a magical she-goat. Aegipan escaped from the monster Typhon with the other gods, by transforming herself into a goat, with a tail and lower body of a fish. See also Typhon in the Creation page.

Aquarius

The Water-carrier was Ganymede, the son of King Tros of Troy. Zeus had abducted the Trojan youth, because he fell in love with the boy. Ganymede served the gods as a cupbearer in Olympus.

Pisces

Aphrodite and Eros escaped from the monster Typhon by leaping into the sea and transforming themselves into fishes. The goddess was grateful for her escape and so immortalised their forms as fishes, by placing them in the sky. See also Typhon in the Creation page.

Info from: www.timelessmyths.com/classical/stars.html