Ancient Greek myths tell us not only how the galaxy got into the night sky but why it came to be called ‘galaxy.’

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Managing editor and logophile Andy Hollandbeck reveals the sometimes surprising roots of common English words and phrases. Remember: Etymology tells us where a word comes from, but not what it means today.

Centuries before the era of ubiquitous light pollution, humankind looked to the night sky in awe and wonder and found a remnant of divine motherhood: a cloudy white streak arcing across the starry sky. They didn’t know exactly what it was, so they created myths about how it got there, attributing its existence to the mischief of the gods.

There are multiple versions of that story, but Zeus, King of the Gods, plays a role in all of them.

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You might recall from your high school mythology class that Zeus’s jealous father, the titan Kronos, was so worried that his children would one day overthrow him that, one by one, he swallowed their infant bodies whole. On the day that Kronos called for infant Zeus to be brought to him, his wife, Rhea, wrapped a boulder in swaddling clothes and passed it off as the sleeping child. Before Kronos swallowed this faux Zeus, he ordered Rhea to nurse him one last time. In this story, the milk that spurted out when she pressed the rock to her breast became that white streak across the night sky.

In another mythical explanation, Zeus duped the human Alcmene into a roll in the hay and impregnated her. After that child (named Alcides) was born, Alcmene, fearing Hera’s wrath for Zeus’s infidelity, abandoned him in a field in Thebes. Athena rescued the child, her half-brother, and, either from her own sense of mischief or at Zeus’s command, brought him to Hera. Hera either did or did not know the infant was Zeus’s illegitimate child — stories differ — but either way, she nursed him at her own breast. In another version of the story, Zeus himself placed the infant Alcides at Hera’s breast while she was sleeping.

Regardless of how Alcides got there, Hera’s milk bestowed godlike strength upon him. But when Hera woke up — or the young demigod clamped down a little too hard, depending on which story you read —Hera pulled him away, and a spurt of her breast milk created that white arc in the night sky.

I don’t know why the ancient Greeks were so obsessed with making breast milk a centerpiece of this myth, but centuries later, we’re still calling that pale white streak the Milky Way. The ancient Greeks called it that too, only not in English. Stemming from the Greek word for milk, gala, they called it Galaxias, which in English became galaxy.

The word galaxy was synonymous with the Milky Way well into the 19th century. Only then, as technology progressed and our understanding of the vastness of the universe grew, did the galaxy (the Milky Way) become a galaxy (one of many). Had the ancient Greeks built their myth around something else that was white — sheep’s wool, lily petals, polystyrene packing peanuts — our astronomical vocabulary might be vastly different today.

To finish the story of the infant Alcides: He was returned to Alcmene and her husband Amphitryon to be raised as a mortal. In a sad attempt to appease the angry Hera, the child was later renamed Heracles, meaning “glory of Hera.” The Romans — and much later, Hollywood — called him Hercules.