In the Greek mythology, it is definitely milk, though the source of the milk and its drinker are not known for certain. It could have been formed by the milk of Hera, which flowed when she realized that she had been giving milk to Hercules and thrust him away. Others have said that Hera intended with her milk to anoint and feed Dionysus in order to heal his madness. Others say that it was the milk of Rhea, which flowed at the time when she presented the stone to Cronos. For many civilizations, heavens are where the souls would go after death, and the Milky Way is the path to be followed for this journey from Earth to God, playing the same role at night as the rainbow during the day.
Some legends coming from very different places are surprisingly similar.
A dog which ran from a corn mill in the south towards the north, dropping meal as he ran, is given as the origin of the Milky Way in Scandinavian legends. The Cherokees, faced with a giant dog stealing their corn at night, chased after him making the loudest noises they could. It ran to the top of a hill, leaped into the sky, the cornmeal spilling out the sides of its mouth, and ran across the black night sky until it disappeared from sight. There are spiral arms in this disk, which are regions of active star formation. An extended dark halo whose composition is unknown.