This is a “re-run” of a post that originally ran on July 21, 2018.
What do the Milky Way and an ancient pilgrimage road in Spain have in common? A name: the Camino de Santiago. Here is a brief discussion from Burnham’s Celestial Handbook:
In Old England it was the Way of Saint James, the equivalent of the Spanish El Camino de Santiago; the name originating, it is said, from a popular legend that Theodomir, Bishop of Idria, was guided by a miraculous star to find the burial place of St. James in 835 AD. From the Field of the Star or “Campus Stella” where the discovery was made evidently comes the title St. James of Compostella. In still another tradition, popular in the Middle Ages, the Milky Way represented the Biblical Jacob’s Ladder upon which the angles descend to Earth.
(Note that James, Iago, and Jacob are essentially the same name.)
The identification of the Milky Way with St. James indeed goes way back. It can be found in a 1660 English-French-Italian-Spanish dictionary entitled Lexicon Tetraglotton:
Johannes Kepler refers to it in his 1618 Epitome of Copernican Astronomy:
The way called by the Greeks the Milky Way and by us the Road of St. Jacob is spread around in the middle of the orb of the fixed stars (as the orb appears to us), dividing it into two apparent hemispheres…
The Milky Way—the Via Lactea—the Milk-white Road—does have the appearance of a path through the sky. However, sometimes you will find the claim that the reason the Milky Way is called the Camino de Santiago is because pilgrims walking the Camino at night can see the Milky Way directly overhead, so that they are walking from East to West in the same direction as the Milky Way. But the fact is that the Milky Way rotates overhead during the night, revolving around the North Star, Polaris, along with the rest of the heavens. So, while it can at times point from East to West, it can also point from North to South, or encircle the horizon. When it passes directly overhead, it runs neither directly East-West nor directly North-South.
So the Milky Way is a Camino without an endpoint. The pilgrim who tries to use just the Milky Way a guide will go absolutely nowhere.