XV THE MILKY WAY OR GALAXY
"Broad and ample road whose dust is gold,
And pavement stars, as stars to thee appear
Seen in the galaxy, that milky way
Which nightly as a circling zone thou seest
Powder'd with stars."
—MILTON, Paradise Lost.
On clear, winter evenings one may see a portion of the zone of the Milky Way, which encircles the heavens, arching magnificently across the heavens as it passes from Cassiopeia and Cepheus in the northwest, through Perseus and Auriga and the eastern part of Taurus, across the feet of Gemini, between Canis Minor and Orion and through the eastern part of Canis Major to the southern horizon.
At this point it passes beyond our range of vision into the star-groups of Puppis, Vela and Carina, subdivisions of the huge southern constellation of Argo Navis. It reaches its greatest distance south of the celestial equator and also attains its greatest brilliancy in Crux, the far-famed Southern Cross. From here it turns northward once more, passing into Centaurus, Musca, Circinus Ara and Lupus constellations of the southern hemisphere and comes within our range of vision again in Sagittarius and Scorpio. Here the Milky Way divides into two branches, though some astronomers now believe that this apparent division into two branches is due to the presence of an enormous cloud of non-luminous matter lying along the course of the Milky Way at this point, similar in its nature to the dark "holes" and "caves" and streaks that appear in all portions of the Milky Way and most noticeably athwart its course in Argo and Centaurus.
One of these branches of the Milky Way passes from Sagittarius through Aquila to Cygnus and the other through Scorpio, Ophiuchus and Serpens to Cygnus, the two extending diagonally across the heavens in the late summer and early fall evenings from the northeast to the southwest. From Cygnus, the Milky Way passes into Cepheus and Cassiopeia and thus completes its circuit of the heavens.
It is not seen to advantage in spring or early summer evenings because it then rests nearly on the horizon. Its plane is inclined about 63° to the celestial equator and its poles lie in the constellations of Coma Berenicis and Cetus. These are the two points that lie farthest from the Milky Way.
The Milky Way has been called the groundwork of the universe. By far the greater number of all the stars are crowded towards its plane in the form of an enormous flattened disk or lens.
Our solar system, it has been estimated, lies close to the plane of the Milky Way and at a distance of some 50,000 or 60,000 light-years from its center.
The diameter of the Milky Way as deduced from Dr. Harlow Shapley's work on globular star clusters is about 300,000 light-years in extent, or ten times greater than the limit set some years ago.
The apparent crowding together of the stars into dense clouds in the Milky Way is partly an effect due to our position in the Milky Way. When we look at the heavens in a direction at right angles to this plane we find comparatively few stars lying along our line of vision because the stars are actually fewer in number in this direction. If we look along the plane of the Milky Way, however, we see to a greater distance through an enormous depth of stars. Though individual stars may not be much closer together in the Milky Way than they are outside of it, there are on the whole more of them and the effect of greater density is produced.
Father Hagen of the Vatican Observatory, who has for years made a study of the dark clouds of obscuring matter and dark nebulæ that abound in space, has found evidence of the existence of many vast clouds of dark obscuring matter over the entire heavens above and below the plane of the Milky Way as well as surrounding the Milky Way in its own plane. The existence of such clouds of non-luminous matter would account partly for the comparative fewness of stars in space outside of the plane of the Milky Way since many stars would be concealed from our eyes by these obscuring clouds. There is, however, in addition, an actual crowding of all the visible stars toward this plane.
The peoples of all ages have honored the Milky Way in story and legend. It has been universally referred to as The Sky River and The Pathway of Souls. To the little Hiawatha, we remember, the "wrinkled old Nakomis"
"Showed the broad white road in heaven
Pathway of the ghosts, the shadows,
Running straight across the heavens,
Crowded with the ghosts, the shadows.
To the Kingdom of Ponemah
To the land of the hereafter."
In The Galaxy, Longfellow thus describes the Milky Way:
"Torrent of light and river of the air
Along whose bed the glimmering stars are seen
Like gold and silver sands in some ravine
Where mountain streams have left their channels bare!"
In Sweden, where the Milky Way arches high through the zenith in winter, it is called the Winter Street, and Miss Edith Thomas writes thus beautifully of it in her poem entitled, "The Winter Street":
"Silent with star dust, yonder it lies—
The Winter Street, so fair and so white;
Winding along through the boundless skies,
Down heavenly vale, up heavenly height.
Faintly it gleams, like a summer road
When the light in the west is sinking low,
Silent with star dust! By whose abode
Does the Winter Street in its windings go?
And who are they, all unheard and unseen—
O who are they, whose blessèd feet
Pass over that highway smooth and sheen?
What pilgrims travel the Winter Street?
Are they not those whom here we miss
In the ways and the days that are vacant below?
As the dust of that Street their footfalls kiss
Does it not brighter and brighter grow?"
Beautiful indeed are these poetic fancies but none of them picture even remotely the awe-inspiring grandeur of the Milky Way as it actually exists.