Page:The American Cyclopædia (1879) Volume XV.djvu/265

 SPECTRUM ANALYSIS Spectroscopic analysis applied to the stars has shown that they resemble the sun in general constitution and condition. But characteristic differences exist, insomuch that the stars have been divided into four orders distinguished by their spectra, types of which are given in fig. 4. These are thus presented by Secchi, who exam- ined more than 500 star spectra : The first type is repre- sented by a Lyras, Sirius, &c., and in- cludes most of the stars shining with a white light, as Al- tair, Regulus, Eigel, the stars ft, y,, f, and TJ of Ursa Ma- jor, &c. These give a spectrum show- ing all the seven colors, and crossed usually by many lines, but always by the four lines of hy- drogen, very dark and strong. The breadth of these four lines indicates a very deep, ab- sorptive stratum at a high temperature and at great pres- sure. Nearly half the stars observed by Secchi showed this spectrum. The second type in- cludes most of the yellow stars, as Ca- pella, -Pollux, Arc- turus, Aldebaran, a Ursse Majoris, Pro- cyon, &c. The Fraunhofer lines are well seen in the red and blue, but not so well in the yellow. The resem- blance of this spec- trum to the sun suggests that stars of this type resem- ble the sun closely in physical constitu- tion and condition. About one third of the stars observed by Secchi showed this spectrum. The third type includes Antares, a Orionis and a Hercu- lis, ft Pegasi, Mira, and most of the stars shi- ning with a red light. The spectra show bands of lines ; according to Secchi there are shaded bands, but a more powerful spectroscope shows multitudes of fine lines. The spectra resem- ble somewhat the spectrum of a sun spot, and Secchi has advanced the theory that these stars are covered in great part by spots like those of the sun. About 100 of the observed stars belong to this type. The fourth type differs from the preceding in the arrangement and appearance of the bands. It includes only faint stars. A few stars, as y Cassiopeise,