Why is the Milky Way called that? And what does milk have to do with it?

Our planet, together with the Sun and the entire Solar System, is located inside a spiral galaxy called the Milky Way. This name comes from the ancient Greeks, who called it galaxias kyklos (“milky circle”, from Greek gala, “milk”) probably because its shape, seen on a night with a clear sky without light pollution, resembles a splash of milk. And it was just a squirt of milk from the queen of the gods Eraaccording to Greek mythology, to give rise to what we now call the Milky Way by abruptly detaching the newborn baby from its breast Heraclesplaced there by his father Zeus while Hera slept. The sudden gesture of the goddess released splashes of milk which, according to mythology, gave rise to the Milky Way. The association of the whitish stripe with a path composed of milk then led the Romans to name it via lactea, from which the name we still use derives directly. The Greek term gala for milk is at the origin of the etymology of the word galaxy.

The Milky Way between astronomy, art and mythology

Like many astronomical objects, the Milky Way also has a strong connection with the mythology Greek and Latin, in particular with the myth of Heracles (Hercules for the Latins). Heracles was the son of Alcmene and Amphitryon, or rather, this is how the story should have gone if Zeus, as often happens, had no hand in it. In reality, the latter is the biological father of Heracles. In fact, while Amphitryon left on an expedition against the Teleboans, Zeus deceives Alcmene by assuming the form and appearance of her husband. From a night of passion and lies between Zeus and Alcmena, Heracles will be born.

There are various legends that tell of how little Heracles, sucking the breast of Era in order to obtain theimmortality, led to the birth of what we now call the Milky Way. According to some traditions it was Hermes, the messenger of the gods, to place Heracles on the goddess's breast, even as she slept. When Hera awoke she pushed the child away and the milk which flowed from its womb and produced a stripe in the sky: the Milky Way.

Another story tells how Alcmena, fearing Hera's jealousy and revenge, exposed her newborn son near Argos. Athena and Hera, who were passing by, saw him. Athena in particular was amazed at Heracles' vigor and beauty, and she asked Hera to offer him her breast. However, little Heracles sucked so hard that he injured the goddess, who was forced to violently throw him away from her. The story has a happy ending: Athena picked up the child and brought him back to her mother, ordering her to raise him without fear.

The origin of the Milky Way by Jacopo Tintoretto, preserved at the National Gallery in London. Via Wikimedia Commons.

What the Milky Way really is

In recent decades we have managed to understand what our galaxy really is: a conglomeration of gas, dust and more than 100 billion stars. In particular, the Milky Way is part of that category of barred spiral galaxies, consisting of a central nucleus cut by a bar and composed of older stars, surrounded by a disk with at least 6 spiral arms composed of gas, dust and stars younger. Our Earth is located right in one of these secondary spiral arms, the arm of Orion, about 27,000 light-years from the center. Although it seems so peaceful, at the center of the Milky Way is a supermassive black hole called Sagittarius A*, with over 4 million solar masses. It's worth saying that this is one of those circumstances in which you live more peacefully in the suburbs!

Image of Messier 83, a galaxy thought to be morphologically very similar to the Milky Way. Credits: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
Acknowledgment: William Blair (Johns Hopkins University).

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