ASTROPHYSICS, the branch of astronomical science which treats of the physical constitution of the heavenly bodies.
It has thus come about that astrophysics owes its recent development, and its recognition as a distinct branch of astronomical science, to the combination of the processes involved in the three arts of spectroscopy, photography and photometry.
From 1872 he held the chair of astrophysics at Leipzig University.
A limit is placed on our knowledge of astrophysics which, up to the present time, we have found no means of overstepping.
The subject of Astrophysics does not admit of so definite a subdivision as that of Astrometry.
He employed in his discussion the radial velocities of 280 stars, spectroscopically determined; and the upshot signally exemplified the community of interests between the rising science of astrophysics and the ancient science of astrometry.
19th century, both the use and the improvement of reflectors were left mainly in British hands; but the gift of the " Crossley " instrument in 1895, to the Lick observatory, and its splendid subsequent performances in nebular photography, brought similar tools of research into extensive use among American astronomers; and they are now, for many of the various purposes of astrophysics, strongly preferred to refractors.
And Astrophysics, xii.
Descriptions of spectroheliographs by Hale, Deslandres, Newall and others, may be found in various papers in Astronomy and Astrophysics, Astrophysical Journal, Comptes rendus, Bulletin astronomique, and other periodicals.
From 1892 to 1895 he was an editor of Astronomy and Astrophysics and thereafter of The Astrophysical Journal.
The field we have defined is divisible into at least two parts, that of Astronomy proper, or " Astrometry," which treats of the motions, mutual relations and dimensions of the heavenly bodies; and that of Astrophysics, which treats of their physical constitution.
Clerke's The System of the Stars (2nd ed., 1905), which contains full references to original papers; Problems in Astrophysics, by the same author,, may also be consulted.
From 1892 to 1905 he was at the university of Chicago as associate professor of astrophysics, as professor (from 1897), and as director of the Yerkes Observatory (after 1895).