Though she returned to Hanover in 1822 she did not abandon her astronomical studies, and in 1828 she completed the reduction, to January 1800, of 2500 nebulae discovered by her brother.
He arranges a selection from his observations on the nebulae in such a way as to give great plausibility to his view of the gradual transmutation of nebulae into stars Herschel begins by showing us that there are regions in the heavens where a faint diffused nebulosity is all that can be detected by the telescope.
Certain stars and nebulae show a bright line helium spectrum.
The results of his observations of nebulae are contained in two catalogues published in the Astronomische Beobachtungen der Grossherzoglichen Sternwarte zu Mannheim, 1st and 2nd parts (1862 and 1875), and those of his variable star observations appeared in the Jahresberichte des Mannheimer Vereins fur Naturkunde, Nos.
Thus in 1864 the spectroscope yielded him evidence that planetary and irregular nebulae consist of luminous gas - a conclusion tending to support the nebular hypothesis of the origin of stars and planets by condensation from glowing masses of fluid material.
It does not, however, seem probable that their apparent anti-galactic tendency has such a significance; in the Magellanic Clouds spiral nebulae are very abundant, a fact which shows that there is no essential antipathy between the stars and the spiral nebulae.
There are other nebulae in which a nucleus can be just discerned, others again in which the nucleus is easily seen, and still others where the nucleus is a brilliant star-like point.
Spiral nebulae have the remarkable characteristic of avoiding the galactic plane, and it has been suggested that the space outside the limits of the stellar universe is filled with them.
What the Nebulae are made of.
Doubtless with improved telescopes many more apparent nebulae would be shown to be clusters, but there are certainly many nebulae which are otherwise constituted.