The Galaxies

Galaxies are large systems of stars and interstellar matter, typically containing several million to some trillion stars, of masses between several million and several trillion times that of our Sun, of an extension of a few thousands to several 100,000s light years, typically separated by millions of light years distance. They come in a variety of flavors: Spiral, lenticular, elliptical and irregular

We live in a giant spiral galaxy, the Milky Way Galaxy, of 100,000 light years diameter and a mass of roughly a trillion solar masses. The nearest galaxy to the Milky Way is Sagittarius Dwarf galaxy. This small galaxy is so close, it is being swallowed up by the Milky Way. It lies 80,000 light years from the Sun and 52,000 light years from the center of the Milky Way. The next nearest galaxy is the Large Magellanic Cloud, 170,000 light years away. The Andromeda Galaxy, also a spiral, is about 2,3 million light years distant.

M31 Andromedina galaksija

Spiral galaxies usually consist of two major components: A flat, large disk which often contains a lot of interstellar matter (visible sometimes as reddish diffuse emission nebulae, or as dark dust clouds) and young (open) star clusters and associations, which have emerged from them (recognizable from the bluish light of their hottest, short-living, most massive stars), often arranged in conspicuous and striking spiral patterns and/or bar structures, and an ellipsoidally formed bulge component, consisting of an old stellar population without interstellar matter, and often associated with globular clusters. The luminosity and mass relation of these components seem to vary in a wide range, giving rise to a classification scheme.
Our sun is one of several 100 billion stars in a spiral galaxy, the Milky Way.

Galaksija M85 u Coma Berenices


These are, in short, "spiral galaxies without spiral structure", i.e. smooth disk galaxies, where stellar formation has stopped long ago, because the interstellar matter was used up. Therefore, they consist of old population stars only, or at least chiefly. From their appearance and stellar contents, they can often hardly be distinguished from elliptical observationally.


M32 Satelit galaksija od M31


Elliptical galaxies are actually of ellipsoidal shape, and it is now quite safe from observation that they are usually triaxial . They have little or no global angular momentum, i.e. do not rotate as a whole (of course, the stars still orbit the centers of these galaxies, but the orbits are statistically oriented so that only little net orbital angular momentum sums up). Normally, elliptical galaxies contain very little or no interstellar matter, and consist of old population stars only. They appear like luminous bulges of spirals, without a disk component.

M82 Cigara galaksija


Often due to distortion by the gravitation of their intergalactic neighbors, these galaxies do not fit well into the scheme of disks and ellipsoids, but exhibit peculiar shapes. A subclass of distorted disks is however frequently occurring.




(C) Copyright 1996 - 2017 by Andjelko Glivar. All rights reserved. This material may not be published in any form without permission.



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