Universe Expansion and measuring the distances through the universe
The universe is the wide and extended space that contains all the galaxies , the stars , the planets , the moons , the living organisms , and everything , The universe is very vast , The Sun and the earth are tiny parts in the universe , And It contains about 100000 million galaxies .
The Galaxies are groups of stars that rotate together in the cosmic space by the effect of gravity , They are bigger ( or structural ) units of the universe .
Each galaxy has a distinctive shape according to the harmony and order of the groups of stars in it , The Galaxies gather in clusters , The Galaxies Clusters are groups of galaxies in the space , The galaxy to which our solar system belongs is Milky Way galaxy .
Milky Way galaxy contains all the stars we see at night in the sky , And It is given that name because it appears in the sky at night as a splashing milk or spreading straw .
In Milky Way Galaxy , The old ( large ) stars gather in the center , The recent small stars are located in the spiral arms of the galaxy , The Sun is a star of millions of stars that rotate around the center of Milky way galaxy .
The Sun takes about 220 million years to complete one rotation around the centre of the galaxy , The Earth is one of the planets that rotate around the Sun , And it is the planet of life .
The distance between the stars are very large , So , the distances in the far space are not measures in kilometers but they are measured in a unit called Light year .
Light year is the distance covered by the light in one year and it equals ( 9460ooo million kilometer ) , 9.467 x 1012 km , The speed of light equals 300000 km / sec .
The distance between the galaxies increase as the time passes as the galaxies move away in the cosmic space , And this is known as Expansion of the Universe .
The Universe is in a state of continuous expansion , The expansion of the universe is the continuous separation between the galaxies , The continuous expansion of the space is due to the continuous motion of galaxies in the universe .
The cosmogony in ancient times
In ancient civilizations , Their relationship with the world of multiple gods and their deep belief that there is a fundamental difference between the earth and heaven did not allow them to develop theories about the universe and its origin .
In the Stone Age , the first human perception of cosmogony was put , where Myths dominated the human imagination , The ancient Egyptians and Babylonians assumed that there was a relationship between the eternal universe and the multiple Gods controlling it .
At both the Indian and Chinese civilizations , The astrology prevailed , Philosophers of Greeks and Romans put theories about the cosmic phenomena .