Transcriber’s Note
Cover image was created by transcriber using an image of the irregular nebula N.G.C. 4214 contained in Plate XIV. The cover is placed into the public domain.
EXTRA-GALACTIC NEBULAE[1]
By EDWIN HUBBLE
[Transcriber’s Note: This etext was produced from
The Astrophysical Journal, Vol. LXIV, pp. 321-369, 1926.]
ABSTRACT
This contribution gives the results of a statistical investigation of 400 extra-galactic nebulae for which Holetschek has determined total visual magnitudes. The list is complete for the brighter nebulae in the northern sky and is representative to 12.5 mag. or fainter.
The classification employed is based on the forms of the photographic images. About 3 per cent are irregular, but the remaining nebulae fall into a sequence of type forms characterized by rotational symmetry about dominating nuclei. The sequence is composed of two sections, the elliptical nebulae and the spirals, which merge into each other.
Luminosity relations.—The distribution of magnitudes appears to be uniform throughout the sequence. For each type or stage in the sequence, the total magnitudes are related to the logarithms of the maximum diameters by the formula,
