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On the macroscopic scale of time, the yuga system is highly evolved in the Indian Astronomy. Many important elements of planets and other parameters are given in terms of the number of revolutions in the course of a long period of time called '''yuga'''.     

On the macroscopic scale of time, the yuga system is highly evolved in the Indian Astronomy. Many important elements of planets and other parameters are given in terms of the number of revolutions in the course of a long period of time called '''yuga'''.     

While in the [[Vedanga Jyotisha (वेदाङ्गज्योतिष्)|Vedanga Jyotisha]] the word yuga was used to mean a period of 5 years, in later works the word meant a large period of time. Yugas of large periods of time have been used to indicate the rates of motion of planets and other important points of astronomical significance. This technique enabled them to express these constants as integers, though very large, thus avoiding very inconvenient fractions.<ref name=":0">Balachandra Rao, S. (2017 Third Edition) Indian Mathematics and Astronomy. Benguluru : Bhavan's Gandhi Center of Science & Human Values</ref>

While in the [[Vedanga Jyotisha (वेदाङ्गज्योतिष्)|Vedanga Jyotisha]] the word yuga was used to mean a period of 5 years, in later works the word meant a large period of time. Yugas of large periods of time have been used to indicate the rates of motion of planets and other important points of astronomical significance. This technique enabled them to express these constants as integers, though very large, thus avoiding very inconvenient fractions.<ref name=":0">Balachandra Rao, S. (2017 Third Edition) Indian Mathematics and Astronomy. Benguluru : Bhavan's Gandhi Center of Science & Human Values</ref> Indian time scales are unique in that they account for the cyclic and linear aspects as seen from the astronomical texts.

=== Yuga in Vedas ===

=== Yuga in Vedas ===

# इद्वत्सरः ॥ Idvatsara

# इद्वत्सरः ॥ Idvatsara

=== चतुर्युगाः ॥ Chaturyuga ===

=== चतुर्युगाः ॥ Chaturyuga in terms of Human Varshas ===

[[File:Kalachakra.png|thumb|653x653px|Yugas and Kalpa ]]Yuga (युगम्) is one of the four large periods into which the basic Chaturyuga cycle is divided, it forms the basic Indian cycle of creation and destruction. According to the puranas and the astronomical texts one Chaturyuga consists of 43,20,000 solar years. Thousand Chaturyugas form a Kalpa, which is the larger cycle of creation and destruction, and is seen as the day of Brahma. The four Yugas comprising the Chaturyuga are:  

[[File:Kalachakra.png|thumb|653x653px|Yugas in terms of Human Varshas ]]Yuga (युगम्) is one of the four large periods into which the basic Chaturyuga cycle is divided, it forms the basic Indian cycle of creation and destruction. Yuga Pramana is calculated in terms of Human varshas and Divya varshas. The following is the first version of Yuga Pramana involving the use of human varshas or years.  According to the puranas and the astronomical texts one Chaturyuga consists of 43,20,000 solar years. Thousand Chaturyugas form a Kalpa, which is the larger cycle of creation and destruction, and is seen as the day of Brahma. The four Yugas comprising the Chaturyuga are:  

# कृतयुगम् ॥ Krtayuga

# कृतयुगम् ॥ Krtayuga

# त्रेतायुगम् ॥ Tretayuga

# त्रेतायुगम् ॥ Tretayuga

# द्वापरयुगम् ॥ Dvaparayuga

# द्वापरयुगम् ॥ Dvaparayuga

# कलियुगम् ॥ Kaliyuga

# कलियुगम् ॥ Kaliyuga

It may be noted that the time period in four yugas are in the ratio of 4:3:2:1. One Mahayuga is ten times a Kaliyuga in its duration. However, Aryabhata I, the ancient Indian mathematician, revised the duration of the four yugas in a mahayuga and made them of equal duration, viz., 10,80,000 instead of the traditional yuga scheme of 4:3:2:1.  

It may be noted that the time period in four yugas are in the ratio of 4:3:2:1. One Mahayuga is ten times a Kaliyuga in its duration. However, Aryabhata I, the ancient Indian mathematician, revised the duration of the four yugas in a mahayuga and made them of equal duration, viz., 10,80,000 instead of the traditional yuga scheme of 4:3:2:1.

==== Krta Yuga  ====

==== Krta Yuga  ====

==== Kali Yuga  ====

==== Kali Yuga  ====

The fourth and the last Yuga of a Chaturyuga cycle. The current Kaliyuga began with the ascendance of Srikrishna from the earth after the Mahabharata war more than 5,000 years ago. Indian astronomical texts fix the time and date of the onset of current Kaliyuga either at the midnight of February 17/18 or the sunrise of February 18 of 3102 BCE (Julian reckoning). Further the mean midnight is as at Ujjaiyini (23^o 11'N Latitude and 75^o 46'E Longitude) meridian passing through Lanka on the equator according to the ardharatrika (midnight) system.<ref name=":0" />  

The fourth and the last Yuga of a Chaturyuga cycle. The current Kaliyuga began with the ascendance of Srikrishna from the earth after the Mahabharata war more than 5,000 years ago. Indian astronomical texts fix the time and date of the onset of current Kaliyuga either at the midnight of February 17/18 or the sunrise of February 18 of 3102 BCE (Julian reckoning). Further the mean midnight is as at Ujjaiyini (23^o 11'N Latitude and 75^o 46'E Longitude) meridian passing through Lanka on the equator according to the ardharatrika (midnight) system.<ref name=":0" />

 

 

 

 

 

 

 

 

=== कल्पम् ॥ Kalpa ===

=== कल्पम् ॥ Kalpa ===

Kalpa is the period of one thousand Chaturyugas or Mahayugas, forming a day of Brahma. A Kalpa is divided into 14 Manvantaras, and there is a Manu, the patriarch, of each of the 14 Manvantaras. The largest Indian time cycle is that of 100 years of the life of Brahma, which is called a Para (परा) and half of it is Parardha (परार्धः). Currently we are in the Vaivasvata Manvantara, the seventh Manvantara of the Svetavaraha Kalpa, which is at the beginning of the second Parardha, or the fifty-first year of the current 100 year cycle of Brahma.

Kalpa is the period of one thousand Chaturyugas or Mahayugas, forming a day of Brahma. A Kalpa is divided into 14 Manvantaras, and there is a Manu, the patriarch, of each of the 14 Manvantaras.  

 

 

The largest Indian time cycle is that of 100 years of the life of Brahma.

 

which is has two divisions Parartha (परार्धः) - Purva Parartha which constitutes the first fifty years of Brahma's age and Dvitiya Parartha which make the later fifty years of Brahma's age.

 

Currently we are in the Vaivasvata Manvantara, the seventh Manvantara of the Svetavaraha Kalpa, which is at the beginning of the second Parardha, or the fifty-first year of the current 100 year cycle of Brahma.

Present Kalpa = Svetavaraha Kalpa   

Present Kalpa = Svetavaraha Kalpa   

Present Mahayuga = 28th (of the 71 Mahayugas)   

Present Mahayuga = 28th (of the 71 Mahayugas)   

Present Chaturyuga = Kaliyuga

Present Chaturyuga = Kaliyuga  

Indian astronomical siddhantas assumed that at the commencement of the Kalpa all the planets including Ketu were in conjunction (at the same celestial longitude) at the first point of Mesha and the ascending node (Rahu) of the Moon was 180 degrees away (i.e., at the first point of Tula).<ref name=":1">Balachandra Rao, S. (2014) Indian Astronomy. Concepts and Procedures. Benguluru : M.P. Birla Institute of Management</ref>

As mentioned above the 100 years of life of Brahma is discussed in this section.  

== शकाः ॥ Sakas or Eras ==

== शकाः ॥ Sakas or Eras ==