Galaxies are massive collections of gravitationally bound gas, dust, stars and dark matter. The name is derived from the greek galaxias what means Milky. Hence the name of our own galaxy , the Milky Way.
Galaxies come in many sizes and forms. There are massive spiral galaxies like our own Milky way which contains many billions of stars and are larger than 100 000 Light years in diameter. Other shapes are barred spirals, elliptical galaxies and irregualr shaped ones. The late Edwin hubble came up with the well known Hubble galaxy classification, also known as the hubble pitchfork, to sort out these different shapes.
Some galaxies are highly irregular in shape. Often this is the result of interactions or collisions with other galaxies which can mutilate the shape of a galaxy considerably. Often these are among the visually most intruiging galaxies. A very fine collection of these is the Arp catalog of peculiar galaxies. One of the best known arp galaxies is Messier 51.
Galaxies don't always live a solitary life. Sometimes the live in groups. A nice collection of such groups can be found in the Hickson catalogue. A well known example of such groups is the Stephan's quintet.
The galaxy nearest to our own Milky way is the great Andromeda galaxy. It's 2.3million lightyears away from us
The nature of galaxies is known for merely 100years
Galaxies can be accompanied by smaller galaxies. Also known as dwarf galaxies. Our own Milky way has two such companions. The Magellanic clouds
© Wouter D'hoye 2016 - Last update February 1st 2015