What Do You Know About Galaxies?

Galaxies is name, which consists of million of stars, all of the starts are attracted to each other by gravitational interaction, and they have a common orbit .according to astronomers there are more then 125 billions galaxies in our universe. The entire stars which are on the sky belongs the earth's galaxy. This is known as Milky Way. A sun which consists of huge mass is just associated with the planet earth and it is just a one star in this galaxy earth. Galaxies not only consists of stars and planets, galaxies also consist of different kinds of atomic gases, molecular hydrogen, nitrogen, carbon, silicon and many others.

When galaxies are viewed from the large telescope, only nearest galaxies shows an individual stars. It's an observation, that is combined light of all the stars in the galaxies. Galaxies exists in variety of forms. Some have globe like appearance with a shining molecule's. A galaxy with such a bright shine is known as elliptical, which consists of oil starts .it also consists of gases, dust particles, and some newly formed stars as well. There is another type of galaxies which is known as spiral galaxy .spiral galaxies look like and flatted disk system .spiral galaxy consists of some oil and some young stars as well.

A galaxy is a huge system that contains billons and billions of stars starting from 10 billion stars and going up to a trillion stars. Our universe consists of billions of galaxies in it. Apart from the stars, a galaxy also has gasses and dust that are kept together by gravity. The word galaxy is derived from a Greek word which means ‘milky’ and is also known as the milky way. One such system is the solar system with the sun as a star. These galaxies usually have an elliptical shape but they may have a spiral and irregular appearance as well. The distance between two galaxies is called intergalactic space. These galaxies may even form new stars and the process is called starburst.

Galaxies are giant clusters of stars. In addition to stars, galaxies contain gases and dust. Our solar system is a part of the galaxy called the 'Milky Way'.

The Milky Way has three main parts: a nucleus, a disc and a halo. There are nearly 10 stars in this galaxy. The spiral shaped galaxy spins slowly in space. From a side, it looks like a disc with a central bulge. The sun is about 30,000 light years from the centre. The diameter of the Milky Way is nearly 120,000 light years and its central thickness is about 10,000 light years.

The Milky Way described above is just one galaxy. There are nearly 10º such galaxies, which are the building blocks of the vast universe.

Galaxies are not fixed in the universe but are moving outward, i.e. we are in an expanding universe. The spectra of light from these galaxies show a frequency shift towards the red, known as the 'red shift'. This shift indicates that the galaxies are moving away. Edwin Hubble made a systematic study of the red shifts of various galaxies and discovered that the red shift is directly proportional to the distance of a galaxy from us.

You get many types of galaxies in the universe. You get spirals, ellipticals and irregular. Ellipticals are by far the most common, followed by spirals and a very small number are thought to be irregulars.

There is a classification system called the "Hubble Tuning Fork Diagram" which shows how astronomers classify galaxies and also how they used to think they evolved (this is now known to be wrong).

Spiral galaxies come in two types, one with a bar at the centre which the arms come off and one where the arms just come straight from the centre. They have a large amount of gas and dust in them and contain old and young stars, with the spiral arms and the centre being the areas where these young stars form. They also hold their shape by rotation.

Elliptical galaxies are the opposite they tend to be older stars with not as much gas and dust, they can look anywhere from a flat oval to a rugby ball in shape. Whereas spirals are very thin and flat. The shape is given by the random velocities of the stars inside. They can also be of two types called "disky" and "boxy" where one looks a lot like a disk and the other like a box.

The latter type that is fairly uncommon are called irregulars, these are galaxies that can't be classified as the other two.

I should note that the ellipticals and spirals can also fall into another sub category called "dwarf ellipticals" or "dwarf spirals". These are galaxies that are very small compared to other galaxies. They are common and tend to orbit around much larger galaxies like our own the Milky Way (our galaxy) which is itself a large barred spiral galaxy.

Galaxies are just planets circling a sun.