XVIITHE MILKY WAY

Like a great river returning into itself, the Galaxy encircles the starry heavens, and those who know only its northern course have no idea of its brilliance and wonderful complexity in its brightest part.

Its light is soft, milky, and almost uniform, between Cygnus and Sirius, but when it enters Argo it becomes extremely broad, and spreads out like a river on a flat marshy plain, in many twisting channels with spaces between. Where Canopus shines on the bank there is a narrow winding ford right across its whole breadth, as if a path had been made by the crossing of a star.

After this it suddenly becomes extremely narrow, but so bright that all the light which was shining in the broad channel seems to be condensed in this narrow bed. In the brightest, richest part the Great Nebula of Argo is easily distinguished by the naked eye. Contrasting with this and other bright condensations are black gaps, the largest and blackest of which is the well-known Coal-Sack near the Southern Cross.

THE MILKY WAY IN SCORPIO, LUPUS,AND ARAPhotographed at Hanover, Cape Colony,by Bailey and Schultz

THE MILKY WAY IN SCORPIO, LUPUS,AND ARA

Photographed at Hanover, Cape Colony,by Bailey and Schultz

The river now divides. One short stream, which goes north from Centaur towards Antares, is faint and soon lost; but another northern stream is so bright and so persistent that from Centaur to Cygnus we may say that the Galaxy flows in a double current. This northern portion forms first the smoke of the Altar on which the Centaur is about to offer the Beast, then passes through the Scorpion into the Serpent-Holder, and here, between η Ophiuchi and Corona Australis, the double stream has its greatest width. The northern division soon grows dim and seems to die out, but begins again near β Ophiuchi, and, curving through a little group of stars, passes through the head of the Eagle and forms an oval lagoon in the Swan.

The southern stream passes through the Scorpion’s Tail into Sagittarius, then through the Eagle and the Arrow till it flows close beside the northern stream in the Swan, and finally rejoins it in a bright patch round α Cygni. Except just here it is much brighter thanthe northern stream, and its structure is even fuller of wonderful detail than in Argo. In Sagittarius it consists of great rounded patches with dark spaces between. The brightest of these contains the star γ Sagittarii; then follows a remarkable region of small patches and streaks, the portion passing through Sagittarius and Aquila being thickly studded with nebulae. This is followed by another bright patch, rivalling that round γ Sagittarii, which involves the stars λ and 6 Aquilae.

This ends the most brilliant and wonderful part of the Milky Way. When well seen, as we see it in the south, it recalls Herschel’s words, written at the Cape when it came into view in his telescope:

“The real Milky Way is just come on in great semi-nebulous masses, running into one another, heaps on heaps.” And again: “The Milky Way is like sand, not strewed evenly as with a sieve, but as if flung down by handfuls, and both hands at once.”

What is it? The ancients thought it the pathway of departed spirits, or fiery exhalations from the earth imprisoned in the skies, or a formerroad of the sun through the stars. But Democritus and some other inquiring Greeks believed it to be the shining of multitudes of stars too faint and too close together to be seen separately, and we know this to be the truth. We know also, from simply counting the stars in different regions of the sky, that their numbers increase regularly as we go from north or south towards the Milky Way, and stars of all magnitudes are most abundant within its course. We saw also that star-clusters and certain kinds of nebulae frequent it, while other kinds avoid it, and that blue and white stars are the most abundant near it, and tend to move through space in planes parallel with it, while the redder stars are scattered and move about in all directions.

Facts like these lead astronomers to believe that the Milky Way has a definite relation with all the visible universe, that even the most distant nebula is not an outlying universe apart from ours, but all are parts of one vast stellar system.

It is possible that the Milky Way, which we see as a great circle, double in one part, is really an immense spiral, and that we arenearest one curve of it, the great southern division which looks so bright. It may be that the spiral nebulae, vast though they are in terms of earthly measurement, are tiny models of one tremendous spiral which enfolds the universe with its coils.

PRINTED IN GREAT BRITAINBY BALLANTYNE, HANSON & CO. LTD.EDINBURGH AND LONDON

Footnotes:[1]Published at 5s.by Gall & Inglis, Edinburgh and London.[2]Stars are classified by astronomers in “magnitudes,”i.e.degrees of brightness, those of first magnitude being the brightest. Stars below sixth magnitude cannot be seen with the naked eye.[3]Compare Aratus:“The Virgin and the Claws, the Scorpion,The Archer and the Goat.”[4]Right ascension in the skies corresponds with longitude on earth, but is more often reckoned in time than in degrees. For instance, R.A. 1 hour 35 minutes, the right ascension of Achernar, means that this star will be on the meridian 1 hour 35 minutes later than the “first point of Aries”—that is, the point at which the equator cuts the ecliptic at the spring equinox, the fundamental point corresponding with Greenwich in earthly longitude.[5]The stars ε and ι Carinae, κ and δ Velorum, form a cross much like the Southern Cross, but less bright, and this is called the False Cross.[6]A “binary” is a system of two stars which are known to be comparatively close together and influencing one another’s movements. A “double star” may be a binary, or the two stars may really be very far apart and have no connection, merely happening to lie one nearly behind the other.[7]Now often called Eta Carinae, since Argo has been subdivided (see p. 7).[8]It is easy to remember the names of the stars in the Southern Cross. Begin at the foot, which is obviously the brightest, and count round the Cross in clockwise direction α, β, γ, δ. κ is beyond β in a line with γ, β.[9]These two astronomers observed at Paramatta, New South Wales, in the early part of the nineteenth century.[10]Also named ξ Toucani.[11]On Scutum in maps where this constellation is not included in Aquila.[12]N. G. C. 7293.

Footnotes:

[1]Published at 5s.by Gall & Inglis, Edinburgh and London.

[2]Stars are classified by astronomers in “magnitudes,”i.e.degrees of brightness, those of first magnitude being the brightest. Stars below sixth magnitude cannot be seen with the naked eye.

[3]Compare Aratus:“The Virgin and the Claws, the Scorpion,The Archer and the Goat.”

[3]Compare Aratus:

“The Virgin and the Claws, the Scorpion,The Archer and the Goat.”

“The Virgin and the Claws, the Scorpion,

The Archer and the Goat.”

[4]Right ascension in the skies corresponds with longitude on earth, but is more often reckoned in time than in degrees. For instance, R.A. 1 hour 35 minutes, the right ascension of Achernar, means that this star will be on the meridian 1 hour 35 minutes later than the “first point of Aries”—that is, the point at which the equator cuts the ecliptic at the spring equinox, the fundamental point corresponding with Greenwich in earthly longitude.

[5]The stars ε and ι Carinae, κ and δ Velorum, form a cross much like the Southern Cross, but less bright, and this is called the False Cross.

[6]A “binary” is a system of two stars which are known to be comparatively close together and influencing one another’s movements. A “double star” may be a binary, or the two stars may really be very far apart and have no connection, merely happening to lie one nearly behind the other.

[7]Now often called Eta Carinae, since Argo has been subdivided (see p. 7).

[8]It is easy to remember the names of the stars in the Southern Cross. Begin at the foot, which is obviously the brightest, and count round the Cross in clockwise direction α, β, γ, δ. κ is beyond β in a line with γ, β.

[9]These two astronomers observed at Paramatta, New South Wales, in the early part of the nineteenth century.

[10]Also named ξ Toucani.

[11]On Scutum in maps where this constellation is not included in Aquila.

[12]N. G. C. 7293.

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