The Homeric Hymns were sung by ancient Greek poets as introductions to longer epics.
The Dioscuri were divine twins, Castor and Polydeuces ( or Pollux); they were the sons of Zeus and Leda. They are the constellation Gemini.
XVII. TO THE DIOSCURI (5 lines)
Sing, clear-voiced Muse, of Castor and Polydeuces, the
Tyndaridae, who sprang from Olympian Zeus. Beneath the heights
of Taygetus stately Leda bare them, when the dark-clouded Son of
Cronos had privily bent her to his will.
Hail, children of Tyndareus, riders upon swift horses!
XXXIII. TO THE DIOSCURI (19 lines)
Bright-eyed Muses, tell of the Tyndaridae, the Sons of
Zeus, glorious children of neat-ankled Leda, Castor the tamer of
horses, and blameless Polydeuces. When Leda had lain with the
dark-clouded Son of Cronos, she bare them beneath the peak of the
great hill Taygetus, -- children who are delivers of men on earth
and of swift-going ships when stormy gales rage over the ruthless
sea. Then the shipmen call upon the sons of great Zeus with vows
of white lambs, going to the forepart of the prow; but the strong
wind and the waves of the sea lay the ship under water, until
suddenly these two are seen darting through the air on tawny
wings. Forthwith they allay the blasts of the cruel winds and
still the waves upon the surface of the white sea: fair signs are
they and deliverance from toil. And when the shipmen see them
they are glad and have rest from their pain and labour.
Hail, Tyndaridae, riders upon swift horses! Now I
will remember you and another song also.