Astronomy is very interesting and mysterious part of science. Most of the studies of the subject are about celestial bodies that have been set apart in very long distances, which could not be easily understood and felt by human beings, by the Super Nature.There are many theories in the science of astronomy. Big Bang theory is one of them which tells how the Universe came to form.

Once all the matters including our sun, planets and other billions of solar systems and energy of the observable Universe were concentrated in one point of infinite density. According to Big Bang theory the Universe expanded from that extremely dense and hot state and continues to expand today. It is also understood that space it self is expanding with its galaxies.

In Astronomy, the Universe is defined as every thing that physically exists. It includes galaxies, billions of solar systems and stars. Still there are many mysterious things exist in our solar system. But our solar system is a tiny thing when we compare it with the bigness of the Universe. Astronomers are saying that Universe is about 13.8 billion years old and at least 93 billion light years across. 1 light year means the distance that travelled by the light continuously for the time period of one year. The light travels in the space at a speed of 3 lacs km/second. We can't even imagine the distance that travelled by the light continuously for one year. Could you imagine the distance between the ends of Universe ?

After the Big Bang, the Universe started to expand to its present form. According to general science physical matter can not exceed the speed of light. But in the Big Bang theory it is stated that two galaxies have been separated by 93 billion light years in 13 billion years. However, the separation is a natural consequence of general relativity by which it is understood that space can grow with no intrinsic limit on its rate; thus, two galaxies can separate more quickly than the speed of light if the space between them grows.

The Great Universe is made of many millions of Galaxies. Galaxies are groups of billions of stars that are held together by the force of gravity. Most of the galaxies are either spiral or elliptical and some of them also in irregular shape.

The Milky Way, The Large Megallanic Cloud, Abell 2029, The Sagittarius Dwarf, Andromeda, Abell 135 IR 1916 are some of the galaxies of the Universe.

The Milky Way

This is our own galaxy in which our solar system exists. The word galaxy means milk in Greek language. Before the use of astronomical telescopes the galaxies looked like a milky or cloudy area in the sky and called so. Our relatively small solar system is one of 100 - 200 billion stars. The diameter of the Milky Way is 1 lac light years. The sun and all the planets in our solar system take about 200 million years to complete one orbit around its centre.

The Large Megallinic Cloud

This is the brightest of all galaxies and visible only in southern hemisphere. It is about 1.7 lacs light years away from our earth and its diameter is 39,000 light years.

Abell 2029

This is the largest galaxy of the Universe with the dia of 5.6 million ligt years which is 80 times greater than our own Miky Way Galaxy. It is about 1,070 million ligt years away from our earth.

The Sagittarius Dwarf

It was discovered in 1994 and the nearest of all galaxies. It is about 70,000 light years away from our earth.

Andromeda Galaxy

This is the most distant in the Universe that can be seen with naked eye. This is 2,309,000 light years from earth. It has about 300 billion stars and diameter of 180,000 ligt years. The light we see now from Anderomeda left there just after the first humans appeared on our earth.

Abell 135 IR 1916

This is the most distant galaxy of our universe. It is amazingly 13.2 billion light years from the earth. In 2004 astronomers at the European Southern Observatory announced the discovery of this Galaxy.

The Universe Calendar

After the Big Bang there were many astronomical and earth events happened including birth and disaster of dinosaurs. All these things have happened in a huge period of time which could not be easily understood by the human brain. The American astronomer Carl Sagan ( 1934-96 ) first suggested a 'cosmic calendar' as a way of helping people understand the history of Universe. He put every event in to the scale of calendar or human year.

In that calendar our Milky Way forms on the first day of May and our earth appears on 12 th September and Moon on 13 th September. All human history is crowded into the last five minutes of the last of the calendar. Recent time in this current world has to be divided into seconds and fraction of second of the Universe Claendar. So every thing that happened in the last 500 years takes place less than the last second of the last minute of the Universe Calendar. Let us watch the events of Universe Calendar.

Date / Time, Event

1 Jan ( mid-night ), Big Bang - Universe forms

15 March, First stars and galaxies form

1 May, Milky Way galaxy forms

8 Sep, Sun forms

9 Sep, Solar system forms

12 Sep, Earth forms

13 Sep, Moon forms

20 Sep, Earth atmoshere forms

1 Oct, Earliest known life on earth

7 Oct, Earliest known fossile

18 Dec, First many celled life forms

19 Dec, First fish

21 Dec, First land plants ; first insects

23 Dec, First reptiles

24 Dec, First Dinosaur

26 Dec, First mammal

27 Dec, First bird

28 Dec, First flowering plant

28 Dec, Dinosaurs extinct

31 Dec ( 11 : 55 PM ), Homo sapiens ( modern human ) appears