[Some Elliptical galaxies are reffered to as Lenticular galaxies, which seem to belong to a different class of galaxies, between Ellipticals and Spirals. They seem to be consisted entirely of old reddish stars at optical wavelenghts, in the contrary to others, consisted mainly of gas, dust and relatively young stars. The shapes of these different galaxies are classified from Eo, spherical to E7, the most elongated, they tend to merge into the So category of galaxies. Once the belief was that Ellipticals evolve into Spirals, but with todays more profound knowledge, the belief seems to point to the fact that galaxies were formed at much the same time. Whether a Protogalaxy gave rise to a Spiral or an Elliptical was a consequence of the speed of its rotation. A higher rotation would drive a galaxy into the condensation of a Spiral shape and at slower velocities would led one to an Elliptical.

The Local Group of Galaxies

Irr = Irregular
E# = Elliptical (# type)
dE = Dwarf Elliptical
 
 

The Local Group

The Milky Way - SBc, Sb, Sc ( ? )	Andromeda, M31 (NGC 224) Sb type	Triangulum, M33 (NGC 598) Sc type	Large Magellanic Cloud - SB type	Small Magellenic Cloud - SB type	IC10 - SB type	M110 (NGC 205) - E6 type	M32 (NGC 221) - E2 type	Barnard's Galaxy (NGC 6822) - Irr type
	other pictures  will be compiled shortly...
NGC 185 - dE3 pec. type	NGC 147 - dE5 pec. type	IC 1613 - Irr type	IC5152 - IAB(s)m IV type	Wolf - Lundmark - Irr type	Fornarx - dE2 type	Pegasus - Irr type	Sculptor - dE3 pec. type	Leo I - dE3 type
Leo II (Leo B) - dE0 pec. type	Leo III (Leo A) - IBm V type	Andromeda I - dE3 pec. type	Andromeda II - dE type	Andromeda III - dE type	Andromeda IV - unknown	Sagittarius - Irr type	Aquarius - Irr type	Sagittarius Dwarf - IB(s)m V type
GR 8 (DDO 155) - Im V type	Ursa Minor - dE type	Draco - dE0 pec. type	LGS 3 - Irr type	Carina - dE type	UGCA 86 - unknown	Sextans A - Ir + V type	Sextans Dwarf - dE3 type	Tuc Dwarf - dE5 type

 

MILKY WAY GALAXY	Type: SBc centered in Sagittarius Arm (though an uncertainty remains, perhaps an Sb or Sc)	Mass: estimated at approximately between 700 billion and 1 trillion solar masses	Dimensions: about 100,000 light-years in diameter	Member of "the local group" 2nd largest of (group of 3 large galaxies and over 30 small)

Earth is a planet orbiting one of at least 200 billion stars that make up a large spiral galaxy called the Milky Way, our own galaxy. Thousands of these stars can be observed with a modest telescope pointed at a given region in the sky. Fewer stars are visible when gazing away from the plane of the system however, in other words, the regions outside the arms. In various regions it seems like one can see "holes" or darker empty areas of space, once believed to be "holes", today however astronomers know that they are caused by the absorption of light by dust composed of carbon, iron and other material. Very large clouds of gas are also present, composing the vast visible areas along with dust particles and myriad stars. Using Radio Telescopes,astronomers have confirmed the disc like shape of the Milky Way, as radio waves can penetrate gas and dust. Also large spiral arms have been detected, 4 of them to be precised. The one reaching closest to the nucleus is named the Centaurus Arm which can be seen in the area of the sky where the constellations Centaurus, Crux and Carina reside. The other arms consist of the Sagittarius, Orion and Perseus Arm, Perseus being the arm that extends farthest from the nucleus. The diameter of the main part of the disc is about 100,000 light-years, although it extends much further in an increasing state and the thickness about 1,000 light-years. Our sun lies about 30,000 light-years from the center. The nucleus of the Milky Way as any other similar galaxy, has a concentrated core of ancient stars, that extends to at least 20,000 light-years and 3,000 light-years in thickness. Very little gas resides in the core though, about 10% by mass. Many star types form the populace of galaxies such as our own, from very old to very young, even new ones being formed at this present moment, continuously known as stars from Population I. Older stars constitute the Population II type. Galaxies are in a continuous motion of rotation at very high speeds as well. Our sun treks around the disk at a velocity of 250km/sec.  It is also known as the Cosmic Year. It has been known that the central region of galaxies emanate a large quantity of X-ray radiation leading us to the famous hypothesis that the nucleus of galaxies might in fact display caracteristics of a Black Hole where, matter is literaly swallowed due to the intense gravitational pull exerted upon it. As a result emiting high-energy radiation.
It is speculated that perhaps the convergence of many old stars in the core, due to their own immense gravity, contribute to the creation of these massive entities taking shape of a vortex. The existence of another form of matter in the universe as also been keeping many astronomers busy for many years. The so called "Dark Matter"that is thought to represent 90% of all the matter in the universe is yet to be detected. The existence of such matter is primordial for the astronomers in understanding the origins and evolutionary pattern of the universe and validating once and for all the famous theories of The Big Bang and the Big Crunch or if the expansion of the universe as come to a complete halt, in other words, to a static phase. (reff: Omega value)