a. 星云的

Nebular \Neb"u*lar\, a.
Of or pertaining to nebul[ae]; of the nature of, or
resembling, a nebula.

{Nebular hypothesis}, an hypothesis to explain the process of
formation of the stars and planets, presented in various
forms by Kant, Herschel, Laplace, and others. As formed by
Laplace, it supposed the matter of the solar system to
have existed originally in the form of a vast, diffused,
revolving nebula, which, gradually cooling and
contracting, threw off, in obedience to mechanical and
physical laws, succesive rings of matter, from which
subsequently, by the same laws, were produced the several
planets, satellites, and other bodies of the system. The
phrase may indicate any hypothesis according to which the
stars or the bodies of the solar system have been evolved
from a widely diffused nebulous form of matter.