Spilled Milk

Hera, jealous of her Zeus
(as you know, he was quite loose)
troubled many demigods
these though, tend to beat the odds
Heracles -- do note the name
destined to achieve much fame
Hera tried to kill at birth
Zeus's genes, for what it's worth
did protect his little ilk
all she got was some spilled milk
Heracles she failed to slay
thus you have the Milky Way