Another feature of the southern hemisphere comprises two patches of light called the Ma gellanic Clouds. These are situated at some distance from the Milky Way, and yet seem to be of the same general nature as the latter. They may be described as two outlying collec tions of very faint stars.
It is found by careful observation and count that the stars of any magnitude seem to be rather thicker in the region of the Galaxy than elsewhere. The smaller the stars the greater the thickness in and near the Galaxy becomes, so that it is probable that a large majority of the very faint stars belong to the Milky Way. Several other peculiarities connected with stars of the Milky Way will be better understood after we have described certain varying char acteristics of the stars.
Naming the Most of the brighter stars, not only those of the first and second magnitude, but a few remarkable ones of fainter magnitudes, had special names assigned to them in ancient and mediaeval times. The oldest and best known of all these names is Arcturus, which is found in the book of Job. The names of Castor and Pollux were also assigned in classic antiquity to the two brightest stars in the constellation Gemini, or the Twins. But most of these special names are derived from designations given by the Arabs, which were supposed to express some peculiarity of the star. There are also quite modern names, Polaris, for example, which designates the Pole Star.
During the past three centuries most of these names have been, to a greater or less extent, replaced by a system of designating the brighter stars in all the constellations, which was intro duced by Bayer about 1600. He assigned to the principal stars in each constellation the let ters of the Greek alphabet, alpha, beta, gamma, etc. Commonly the first letter of the alphabet is assigned to the brightest star, and the prog ress of the letters indicates, to a certain extent, the successive orders of brightness in the same constellation. But this rule was not uniformly carried out; frequently the successive letters taken in alphabetical order designate the stars which follow each other in position. For ex ample, in the familiar constellation of the Great Bear, the first six letters of the alphabet are ap plied to the consecutive stars which make up the Dipper. The Greek alphabet not being suffi
cient for all the stars, letters of the Roman alphabet are used when the Greek one is ex hausted. Flamstead, Astronomer Royal at Greenwich, two centuries ago adopted the plan of numbering the stars in each constellation. Any such system, however, is imperfect, and, taken altogether, there is a lack of uniformity in the method of designating the stars, except the brighter ones. The following are a few of the brighter and best-known stars which have well-known names.
Individual name Name on Bayer system Alcyone Eta Tauri Aldebaran Alpha Tauri Algol Beta Persei Antares Alpha Scorpii Arcturus Alpha Bootis Bellatrix Gamma Orionis Betelguese Alpha Orionis Canopus Alpha Argus (Carina) Capella Alpha Aurigae Castor Alpha Geminorum Fomalhaut Alpha Piscis Australis Mira Ceti Omicron Ceti Mizar Zeta Ursa Majoris Polaris Alpha Ursie Minoris Pollux Beta Geminorum Procyon Alpha Canis Minors Regulus Alpha Leonis Rigel Beta Orionis Sirius Alpha Canis Majoris Spica Alpha Virginis Vega Alpha Lyre Spectra of the Stars.— When the spectro scope was • invented and applied one of the first uses made of it was to analyze the light coming from various stars in or er to see in what respect they differed in their constitution. The result has been to show that, out of several thousand stars which have been examined in detail, it can hardly be said that any two are exactly alike. It is true, in the highest branch of science, that one star differeth from another star, not only in glory, but in the substance which makes it up, as well as in various other features. At the present time the spectra of the stars are best studied by means of photog raphy. The general fact that lights can be photographed which are too faint to be visible to the eye is here applied with great success. When only eye methods were used, it was hardly possible to accurately define or measure the spectral lines given by any but the brightest stars, and even here the measures were so un certain that few definite results were reached. But, by applying photography, the negative on which the spectrum is impressed can be placed under a measuring engine, and the settings made by means of a microscope with the highest de gree of precision that admits of being reached.