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Astronomers classify galaxies based on their overall shape (elliptical, spiral or barred spiral) and further by the specific properties of the individual galaxy (for example degree of ellipse, number of spirals or definition of bar). The system of galaxy classification is called the Hubble "tuning fork" diagram, and is the Hubble sequence. In ancient Greece and other early civilizations, astronomy consisted largely of astrometry, measuring positions of stars and planets in the sky. ...
This article is about a celestial body. ...
An elliptical galaxy is a type of galaxy in the Hubble sequence characterized by the following physical properties: The giant elliptical galaxy NGC 4881 (the spherical glow at upper left) lies at the edge of the Coma Cluster of Galaxies. ...
A spiral galaxy is a type of galaxy in the Hubble sequence which is characterized by the following physical properties: Spiral Galaxy M74 presents a face-on view of its spiral arms. ...
NGC 253, a barred spiral starburst galaxy (2MASS). ...
The Hubble sequence is a classification of galaxy types developed by Edwin Hubble in 1936. ...
The "tuning fork" system
 Tuning-fork style diagram of the Hubble sequence The Hubble "tuning fork" diagram starts from the left with elliptical galaxy as its base. Elliptical galaxies can be named from E0 to E7. E stands for elliptical while the number indicates how oval-shaped the ellipse is with 0 being ball shape (in other words, a giant globular cluster) to 7 being discus shape. Technically speaking, the number is ten times the eccentricity. For example, an E7 galaxy has an eccentricty of 0.7. A tuning-fork diagram of the Hubble galaxy classification scheme. ...
A tuning-fork diagram of the Hubble galaxy classification scheme. ...
An elliptical galaxy is a type of galaxy in the Hubble sequence characterized by the following physical properties: The giant elliptical galaxy NGC 4881 (the spherical glow at upper left) lies at the edge of the Coma Cluster of Galaxies. ...
A globular cluster is a spherical bundle of stars (star cluster) that orbits a galaxy as a satellite. ...
After the elliptical galaxies the diagram splits into two branches. The upper branch covers spiral galaxy also called lenticular galaxies. It starts off with S0. The "S" means lenticular, the "0" means no arms, and the subscript number indicates how heavily a stripe is absorbed out of the image of the galaxy by dust in the galactic disc. On the same branch are the next 3 types which all have spiral arms. The "S" here also means lenticular, but the lower case letter after it tell how wound up the arms are. They range from "a" to "d" having the following meanings: A spiral galaxy is a type of galaxy in the Hubble sequence which is characterized by the following physical properties: Spiral Galaxy M74 presents a face-on view of its spiral arms. ...
- Sa - tightly-wound, smooth arms, and a bright central disc
- Sb - better defined spiral arms than Sa
- Sc - much more loosely wound spiral arms than Sb
- Sd - very loose arms, most of the luminosity is in the arms and not the disc
The lower branch of the diagram covers spiral-barred galaxy given the symbol "SB". This branch starts with SBO galaxies which is followed by a subscript number that indicates how heavily defined the bar is. After that the branch continues with the SB galaxies which have lower case letters after them that indicates how heavily defined the bar is. They range from "a" to "c" having the following meanings: Wikipedia does not yet have an article with this exact name. ...
- SBa - a bright center and tight spirals
- SBb - better defined arms than SBa galaxy and are more loosely wound
- SBc - even looser arms, and a much dimmer central portion of the galaxy
The Milky Way Galaxy is now believed to be an SBb galaxy; previously, it was thought to be Sb like its giant companion, the Andromeda Galaxy. This article is about the galaxy called the Milky Way. ...
This image is a Galaxy Evolution Explorer observation of the large galaxy in Andromeda, Messier 31. ...
The de Vaucouleurs system There is an extension to the Hubble sequence that is in wide use, these are the de Vaucouleurs extensions. -
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