He arranged the different groups of galaxies in what became known as the Hubble sequence.

A slightly more extensive description of galaxy types based on their appearance is given by the Hubble sequence.

Irregular galaxies do not fall into any of the regular types of the Hubble sequence.

On the right of the Hubble sequence diagram are two parallel branches encompassing the spiral galaxies.

In 1936 Hubble produced a classification system for galaxies that is used to this day, the Hubble sequence.

To this day, the Hubble sequence is the most commonly used system for classifying galaxies, both in professional astronomical research and in amateur astronomy.

"Variation of Physical Properties along the Hubble Sequence."

Although strictly part of the de Vaucouleurs system of classification, the Sd class is often included in the Hubble sequence.

The Hubble sequence is a morphological classification scheme for galaxies invented by Edwin Hubble in 1926.

Galaxies that do not fit into the Hubble sequence, because they have no regular structure (either disk-like or ellipsoidal), are termed irregular galaxies.

The star spectral classification and discovery of the main sequence, Hubble's law and the Hubble sequence were all made using photographic paper.

Lenticular galaxies are often considered to be a poorly understood transition state between spiral and elliptical galaxies, which results in their intermediate placement on the Hubble sequence.

In the extended Hubble sequence, the Magellanic irregulars are usually placed at the end of the spiral branch of the Hubble tuning fork.

The de Vaucouleurs modified Hubble sequence is a widely used variant of the standard Hubble sequence.

An Irr-I galaxy (Irr I) is an irregular galaxy that features some structure but not enough to place it cleanly into the Hubble sequence.

The de Vaucouleurs system for classifying galaxies is a widely used extension to the Hubble sequence, first described by Gérard de Vaucouleurs in 1959.

Elliptical galaxies and lenticular galaxies are also called "early-type" galaxies (ETG), due to their position in the Hubble sequence.

In the modified Hubble sequence galaxy morphological classification scheme of French astronomer Gérard de Vaucouleurs, Messier 87 is categorized as an E0p galaxy.

Sc and SBc galaxies, for instance, have very "loose" arms, whereas Sa and SBa galaxies have tightly wrapped arms (with reference to the Hubble sequence).

Later observations (by Hubble himself, among others) showed Hubble's belief to be correct and the S0 class was included in the definitive exposition of the Hubble sequence by Allan Sandage.

This nomenclature is the source of the common, but erroneous, belief that the Hubble sequence was intended to reflect a supposed evolutionary sequence, from elliptical galaxies through lenticulars to either barred or regular spirals.

Edwin Hubble classified spiral galaxies of this type as "SB" (spiral, barred) in his Hubble sequence, and arranged them into three sub-categories based on how open the arms of the spiral are.

A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence.

Since the Hubble sequence is entirely based upon visual morphological type, it may miss certain important characteristics of galaxies such as star formation rate (in starburst galaxies) and activity in the core (in active galaxies).

Galaxies come in a great variety of shapes and sizes (see the Hubble Sequence), from giant, featureless blobs of old stars (called elliptical galaxies) to thin disks with gas and stars arranged in highly-ordered spirals.