Swati: the one that stands apart, the gist

Swati: the one that stands apart

The fifteenth of the moon's twenty-seven stations is named for Arcturus, a star that is visibly leaving its neighbours behind, and the essay follows that motion through one evening, through two thousand years, and out through the galaxy.

This is the short way in. The essay has the working, the sources and the sky.

Arcturus has moved a full degree across the sky since the Greeks wrote down where it was. That is two and a half full moons laid end to end, and it is how anybody first worked out that stars move at all.

Every star in the sky is moving. Almost none of them move enough for a person to notice, so we treat the shapes of the constellations as fixed furniture. They are not fixed. They are only very slow.

Arcturus is the one bright star where the movement shows. It shifts a little over two seconds of arc a year. A second of arc is a very small angle: the full moon is eighteen hundred of them wide. So Arcturus needs nearly eight hundred years to cross the width of one full moon, which no person will ever watch happen. But it is fast enough to catch with old records. In 1718 Edmond Halley set Arcturus, Sirius and Aldebaran against a Greek star catalogue almost two thousand years older, found all three had shifted by more than half a degree, and drew the conclusion that the stars move.

Part of why the movement shows is that the star is close, about thirty-six and a half light years away. It is an orange giant: roughly as heavy as the sun, twenty-five times as wide, and around seven thousand million years old.

It is also an outsider. It carries about a third as much iron as the sun, which is a mark of an old star, and it is crossing our part of the galaxy at 122 kilometres a second instead of turning along with it. Fifty-two other stars share that motion. Astronomers have not agreed on where the group came from.

Our own list calls the star Swati and puts the wind god Vayu behind it. The name is usually read as the good goer, the one that goes far. From there the handbooks produce a paragraph telling readers that they are independent and dislike being told what to do, which is a description almost nobody would reject. The essay offers something more useful instead: independence is an arrangement rather than a personality, and arrangements have prices in them and other people in them.

Words decoded

nakshatra (नक्षत्र): one of twenty-seven slices of sky, one for roughly each night the moon takes to travel all the way round
Swati (स्वाति): the fifteenth of those slices; the word is usually read as the good goer, or the one that goes far
Arcturus: the bright orange star the slice is named for; the name is Greek and means guardian of the bear, because it follows the Bear across the sky
Boötes: the constellation Arcturus sits in, drawn in the West as a herdsman
Saptarishi: the seven bright stars the West calls the Plough or the Big Dipper; the curve of their handle points the way to Arcturus
proper motion: a star's own slow movement across the sky, separate from anything the earth is doing
second of arc: a very small angle; there are 3,600 in one degree, and the full moon is about 1,800 across
light year: the distance light travels in a year, so a star thirty-six light years off is seen as it was thirty-six years ago
orange giant: a star that has used up the hydrogen at its core, swollen, and cooled at the surface, which is why it looks orange
precession: the slow wobble of the earth's axis, which shifts the whole sky at once and is a different thing from a single star moving
ecliptic: the line the sun traces through the stars over a year; the moon never strays more than about five degrees from it
Arcturus stream: a group of fifty-three stars, Arcturus among them, all moving the same way through the galaxy for reasons nobody has settled
sidereal reckoning: the way Indian almanacs measure positions against the stars themselves rather than against the seasons
Vayu (वायु): the wind god who presides over this station
prana (प्राण): breath; later texts treat the wind and the breath as one thing

Why anyone should careThere are two kinds of statement in astrology writing, and this station puts them side by side. One is checkable: Arcturus has moved, by this much, since a named person wrote down where it was, and anybody with the old catalogue and a straight edge can confirm it. The other is a compliment, and the compliment about Swati is that you are independent and do not like being told what to do. Almost nobody would refuse that description, which is what makes it worthless as information. Learning to tell the two apart is most of what protects a person in a consulting room.

Read it properly, 7 min Swati: the one that stands apart