Another problem with the nebular hypothesis was the fact that, whereas the Sun contains 99.9 percent of the mass of the solar system, the planets (principally the four giant outer planets) carry more than 99 percent of the system's angular momentum.
Because the theory of Laplace incorporated Kant's idea of planets coalescing from dispersed material, their two approaches are often combined in a single model called the Kant-Laplace nebular hypothesis.
March 7, 1792 Slough, England May 11 , 1871Collingwood, England Sir John Herschel, 1st Baronet, in full Sir John Frederick William Herschel, 1st Baronet (born March 7 , 1792 Slough, Buckinghamshire, England died May 11 , 1871 Collingwood, Kent) English astronomer and successor to his father, Sir William Herschel, in the field of stellar and nebular observation and discovery.
The chemical composition of H II regions (the numbers of atoms of each chemical element, relative to hydrogen) can be estimated from nebular spectra.
The idea that stars are formed by the condensation of gaseous clouds was part of the 19th-century nebular hypothesis (see above).
Sir John Herschel, 1st Baronet, in full Sir John Frederick William Herschel, 1st Baronet (born March 7 , 1792 Slough, Buckinghamshire, England died May 11 , 1871 Collingwood, Kent) English astronomer and successor to his father, Sir William Herschel, in the field of stellar and nebular observation and discovery.
In the early decades of the 20th century, several scientists decided that the deficiencies of the nebular hypothesis made it no longer tenable.
The nebular temperature can be estimated directly from collisional lines alone by comparing emission lines from high-energy levels, populated by collisions, with lines from lower levels.
Others, following Herschel's own speculations, thought of them simply as gaseous clouds relatively small patches of diffuse matter within the Milky Way Galaxy, which might be in the process of developing into stars and planetary systems, as described in Laplace's nebular hypothesis.
Once sufficiently high pressures and densities were achieved in the compacted nebular core, nuclear fusion reactions within it could begin, giving birth to a star.
