The myth: Heracles, Hera and the spilled milk
The story begins as a legitimacy problem. A Hellenistic work ascribed to pseudo-Eratosthenes holds that sons of Zeus could be divine only if Hera had suckled them,[4] and Heracles, a son Zeus had fathered elsewhere, needed that blessing.
So Hermes carries the infant up to Olympus and sets him at the breast of the sleeping goddess. In the Katasterismoi, a first-century CE text credited to pseudo-Eratosthenes that draws on older sources, Hera wakes, discovers the trick and pushes Heracles away, and the milk still flowing is spilled across the heavens to form the Galaxy.[1][6][5]
Nothing about the myth is fixed. Accounts differ on whether Zeus or Hermes does the carrying,[7] and one variant has part of the spilled milk fall to earth and turn into lilies.[8] Tintoretto painted the heavenly version as The Origin of the Milky Way, which hangs in the National Gallery in London.[9]
From galaxias to via lactea to Milky Way
The word does most of the work. Ancient Greek named the Milky Way galaxias, and the word means simply milky.[11] Roman writers translated the idea as Via Lactea and also borrowed galaxias itself, which then travelled through medieval Latin into English.[12]
The English phrase turns up in Chaucer's House of Fame, where the poem points to the Galaxie, which men call the Milky Wey because it is white, and adds that some call it Watling Street.[14] That passage, from the late fourteenth century, is among the earliest known uses of the phrase.[15]
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NamibRand is Africa's only Gold Tier Dark Sky Reserve: extreme Namib Desert isolation, the Southern Cross, Magellanic Clouds, and luxury safari lodges.
Astronomers did not recognise the band as one galaxy among many until the twentieth century, so for most of English's history "Milky Way" was a myth carried inside a plain description.[16] I find that more striking than the myth itself: a goddess's breast survives in every atlas.
Roads, rivers and birds: what other cultures saw
Greek mythology is not the only way people have read the band, and most other names are gentler. The same few images keep returning:
- The Greeks and Romans also saw a road, travelled by the Sun or the gods.[17]
- Spain and Portugal call it the Road to Santiago, after the pilgrim route to Santiago de Compostela.[18]
- The commonest Arabic name is the Straw Way, after straw dropped by farmers heading home from the fields.[19]
- Finland, Estonia and the Baltic states call it the Birds' Path, because migrating birds seem to follow its arc.[20]
- The Lakota name is the Spirit Road and the Cheyenne name the Hanging Road.[21]
- In China it is the Silver River, where the Cowherd and the Weaver Girl, Altair and Vega, meet once a year on the seventh day of the seventh lunar month.[22]
- In India it is the Heavenly Ganges.[23]
- Quechua and Aymara speakers say every earthly river flows into the celestial river Mayu, which replenishes them.[24]
Astrophysicist Or Graur observes that people separated by oceans and centuries keep reaching for the same images.[25] I would add a practical reason: it is the one continuous feature in a sky otherwise made of dots, so a path of some kind was close to inevitable. How much of that continuity you see depends on the sky and the instrument, a difference the Death Valley naked-eye versus camera comparison works through.
Dark constellations: the names written in the gaps
The Western tradition names what is bright. Andean sky-watchers read the opposite, seeing animal shapes in the shadowy parts of the band, among them a llama suckling her baby.[27]
The best-known case is Australian. The emu in the sky is made not of stars but of dark clouds within the Milky Way, and it matters in many different cultures across the continent.[28]
I think this is the tradition worth stealing if you are learning the sky. Find the dark lane before you look for the bright core, and you have the shape the older names depend on. Learning to photograph the Milky Way trains that habit too, because exposure settings force you to look at what the band is made of.
The sky that named the galaxy is fading
More than a third of humanity cannot see the Milky Way, including 60% of Europeans and nearly 80% of North Americans, according to the 2016 world atlas of artificial night sky brightness.[3] The same atlas puts more than 80% of the world's population under light-polluted skies.[29]
Dan Duriscoe, a National Park Service scientist who worked on the project, links that loss to the stories: once the dark views go, the ancestral stories about celestial phenomena are all but forgotten.[30] That is a sharper way to put the stakes than a lost photo opportunity. Every name above, from the Straw Way to the Hanging Road, was coined by someone looking at a band they could not miss.
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The mechanism is skyglow, and why we lost the Milky Way traces it through the atlas and later observations. To test the Greek image against the real thing, run the night in this order:
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- Pick a night near the new moon, or one where the moon rises late.[31] From the northern hemisphere, summer and fall evenings are the season.[32]
- Drive 20 to 30 miles or more from the city limits,[33] and treat Bortle 3 or 4 as the minimum for a good evening.[34] Certified places make the choice easy: Aoraki Mackenzie in New Zealand, which describes itself as the largest reserve in the Southern Hemisphere,[35] Galloway Forest Park in Scotland[36] or Zion in the United States.[37]
- Switch off your lights and give your eyes 20 to 30 minutes.[38] One glance at a phone screen or a streetlight restarts the clock.[39]
- Look for the dark lanes before the bright band, the habit the Andean and Australian names were built on.
- Set expectations by Bortle class. At 4 the band is still impressive but loses most of its structure,[40] at 5 it looks washed out overhead[41] and at 2 it is richly structured to the naked eye.[42]