Page:The Music of the Spheres.djvu/138

 Milky Way are now generally accepted to be dark nebulous matter which cuts out the light from the stellar regions behind them. Professor Barnard made many wonderful photographs of such dark spots and compiled a famous Catalogue of 182 Dark Markings in the sky. of the Mount Wilson Observatory found that in its normal state a nebula is dark rather than luminous. If a nebula shines it is because it is either illuminated by the light from the stars near it or because it is electrically excited in some way not clearly understood.

There is also a Cross on the Milky Way with a dark nebula beside it in a conspicuous position in the southern hemisphere, although there the cross is not quite as perfect as our cross in the north, for it is formed of only four bright stars instead of five. Even our cross is not quite perfect, for one star, the "diamond-studded nail" holding it together, is just a little out of line. in "Earth and Sky" has said that her fingers fairly "itch to put it where it belongs." Imagine! And since she has so aptly expressed it, we now all feel that way.

This outlined figure of the great Northern Cross forms the basis of a constellation called Cygnus, the Swan. The bill of the Swan lies on Albireo, the double star at the foot of the Cross, while its wings curve gracefully back from the armpiece.

According to the story of Phaethon and Cycnus, Phaethon, after his hectic ride in the sun-chariot, fell a "charred fragment" into the river Eridanus. Jupiter's thunderbolt had hit its mark: