Universe Expansion and measuring the distances through the universe

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 .

Milky Way Galaxy

Milky Way Galaxy

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 solar system is the Sun and eight planets revolving around it , The solar system is located in one of the spiral arms of the Milky Way on the edge of the 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 .

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