Our solar family (the sun and the planets) is situated in one corner of one of the two arms of the Milky Way Galaxy. It is in this part of the galaxy, the sun with its family as one unit revolves around a dark companion and completes one orbit in a period of 24,000 years. 

Besides the light and different forms of electro-magnetic energies coming to our planet from our Sun, we also receive light and energy from the center of our Galaxy. According to ancient Indian Masters the light and energies coming from this Galactic center has a very special influence upon all life on earth. It nourishes and helps to develop that intelligence and consciousness which makes us aware of the Divine in all things and act according to its Will. 

When the Sun in its orbit is in such a way that the dark companion comes between it and the Galactic center then the light coming from there is greatly reduced. At such times human intelligence and consciousness is very low and the earth passes through the materialistic age. When the Sun moves on the opposite side and is open to reception of the energies coming from the Galactic center then there is an increase of consciousness and human civilization passes through a very high spiritual age. 

Ancient Indian Masters divide these time cycles in four distinct phases and each phase is called a ‘Yuga'. The word Yuga stands for a specific period of time. This period can be as small as just 12 years when it is used in the context of individual human evolution and it can be as large as thousands of years or even millions of years depending on the astronomical context in which the word is being used. There are four Yugas and in the present context its duration as fixed by the ancient Indian Master Manu in his famous book Manu Smriti is as under (fig - 99). 

The total for all the four yugas is 12,000 years.  
Each precessional cycle is divided into two halves. One the Ascending half in which the sun is moving towards the point on its orbit closest to the Galactic center and a Descending half in which the sun is moving towards the point farthest from the Galactic center.. In the ascending half we move from Kali to Satya and in the descending half we move from Satya to Kali. This creates one cycle. 

Characteristics of each Yuga  

Satya (Truth) 
This is the spiritual age for the whole humanity. Average human intelligence and consciousness in this age is at its highest. Moral and ethical values of average human being is at its best. Comprehension of the spiritual dimension of our being and the Universe is at its highest. Relatively many people attain to states of cosmic consciousness in this age. Relation between man and his Maker is well known and Divine will is known and respected in most matters. In Indian tradition the Bull of Dharma in this age has all its 4 legs intact. In Greek mythology