![]() The interacting galaxies may be formed as a result of a collision between galaxies that fail to merge. Other types of galaxies include interacting galaxies which play an important role in the galactic evolution. Examples of irregular galaxies include Irr I and Irr II. The galaxies do not have outstanding shape or the expected central nuclear and are bluer in color than the arms and disk of a spiral galaxy. ![]() The examples of the irregular galaxies are made up of highly irregular collections of bright areas. The SBc galaxy has both the bar and the arms resolving into star cloud. The SBb galaxies also have smooth bars and relatively continuous and smooth arms which may start near the end of the bar. the nucleus of the SBa galaxies are bright while the smooth spiral arms emanate at the end of the bar. The barred galaxies are designated SB followed by a, b, or c. The spiral arms are protruding and contain several irregularly distributed star cloud and interstellar elements. Sc galaxies have a small nuclear and several open spiral arms. The Sb galaxies contain stars, star clouds, and interstellar elements. The arms of the galaxies are relatively widespread than the Sa variety. Sb galaxies are the intermediate type of spirals galaxies having a medium-sized nucleus. Examples of Sa galaxies include NGC 1302 and NGC 4866. The galaxies have an amorphous bulge at the center. Sa galaxies are normal spiral galaxies with a tightly wound spiral arms which are visible. The two classes are further subclassed into three classes depending on the size of their nucleus. The normal spiral galaxies are indicated by S followed by letters a, b, or c while the barred spirals are designated SB. The arms and the disk of the galaxies are blue in color while the central portions are red like in the case of the elliptical galaxies. The nucleus is sharp-peaked and has a smooth texture and can be small in size. The spirals galaxies are composed of rotating sets of stars and interstellar elements and older stars. ![]() The arms of the normal spirals originate from the nuclear while the barred spirals have bars that straddle the nucleus while the arms unwind from the bar. The galaxies are further divided into normal spirals and barred spiral. ![]() Spiral galaxies are circular in shape, resembling spiraling pinwheels. The subclasses of the galaxies are distinguished by their shapes which are not necessarily three-dimensional shaped. Elliptical galaxies have red colors with their spectra suggesting that their light is emitted from mainly the old stars. Most of the enormous elliptical galaxies are found next to the center of the large galaxy clusters. Many of the elliptical galaxies are formed due to the interaction of galaxies which leads to collisions and mergers with the galaxies capable of growing to enormous sizes compared to other classes of galaxies. The stars forming the galaxies contain light elements since the formation of stars ends after the first burst. The galaxies are, therefore, dominated by old and more evolved stars. The rate of formation of new stars is greatly reduced due to the low portion of the open cluster. Elliptical galaxies have little interstellar matter and structure, and also have a low portion of open clusters. They have an ellipsoidal profile giving them an elliptical appearance irrespective of the angle from which they are viewed. Elliptical GalaxyĮlliptical galaxies were classified by Hubble on the basis of their ellipticity which ranges from E0 to E7 and has a rotational symmetry. However, Hubble’s classification may miss some of the important features including the star formation rate and activities within active galaxies. The classification depended on the visibility of the images observed on the photographic plate. The system of classification of galaxies was first proposed by Edwin Hubble in 1926. Galaxies are divided into three general classes: elliptical, spiral, and irregular. The estimated number of observable galaxies range from 200 billion to 2 trillion or more containing stars that outnumber all of the grains of sand on the planet. Galaxies are different in shape due to the systems of their formation and how they evolve. They exist in clusters that are further grouped into enormous clusters. Nature has provided a wide range of galaxies including faint and dwarfed objects and bright spiral-shaped galaxies. The term galaxy derives itself from the Greek word galaxias, meaning "milky". What Is A Galaxy? Hubble2005-01-barred-spiral-galaxy.Ī galaxy is a system of stars and interstellar matter which makes up the universe.
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