"O'Ryan was a man of might when Ireland was a nation." A poacher, he gives a meal to St. Patrick and is promised a place in heaven in return. Told there is good hunting there, he accepts. Now the other constellations fear his shillelagh
Needless to say, the mythology in this song is distorted (as is the astronomy, for that matter; Venus, Mars, and Orion follow separate courses. Even so, the author must have known some astronomy, as he mentions "a lion, two bears, a bull, and cancer" among the constellations -- i.e . Leo, Ursa Major, Ursa Minor, Taurus, and Cancer the crab).
The story of Orion varies according to different sources, but it is generally agreed that the goddess Eos, not Aphrodite, went after him, and in the end it was Artemis who killed him.
The timing is also wrong, even if you allow that "Ireland was [once] a nation" (it wasn't). Saint Patrick was active in the fifth century of the Christian Era, and we have references to Orion as far back as Homer (Iliad xviii.488 mentions his place in the constellations, and Odysseus encounters his spirit in Odyssey xi.572). - RBW