Spiral galaxies are the most numerous among the larger galaxies. The nearest spiral galaxy to us is the Andromeda Galaxy, which is 2300000 light-years away from us.
There is more than one type of spiral galaxy. Our galaxy, the Milky Way, is a spiral galaxy. It is 20000 light-years thick at the center, 1500000 light-years in length, and has a disk 1500 light-years thick. One different type has big hubs, or centers, and arms that spiral close to the hub. There are two more types besides that one. They are the Seyfert and barred galaxies. Barred galaxies appear to have a bright bar running through the middle.
Seyfert galaxies were discovered in 1943 by Carl Seyfert. Seyfert galaxies measure a few hundred light-years across. The center of a Seyfert galaxy is small but very bright and is made up of seething hot gas in violent motion. The energy in the center is believed to be produced by violent explosions inside the galaxy.
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ELLIPTICAL GALAXIES
Elliptical galaxies look like a stretched out circle. There is a scale of 0 to 7 to designate the roundness of an Elliptical galaxy (created by Edwin Hubble). Elliptical galaxies make up 17% of the brightest galaxies because they are made up of mostly stars and have little or no dust and gas. Elliptical galaxies are much smaller than Spiral galaxies, the smallest being only 3000 light-years in diameter (that’s small for a galaxy) and the largest has a diameter of 10000 light-years.
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Irregular galaxies have no special shape. The smallest irregular galaxy is only 9000 light-years wide, and the nearest Irregular galaxies to us are the Large Magellanic Cloud and the Small Magellanic Cloud (both are or less than 200000 light-years away from the Milky Way), which were named after the explorer Magellan, who first viewed them hundreds of years ago.
Dwarf galaxies are globe-shaped clusters of dim stars, and are only about a few hundred light-years across. Dwarf galaxies may be far more numerous than the larger galaxies.
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*The pictures on this page are given by NASA
http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-faq.html#use