There are 27 Yog in a lunar month as per Hindu astrology and
Panchangs. Each yog measure 13 degrees and 20 minutes – considering the 360
degrees of astrology calculation. Yogas are similar to Nakshatra in calculation
but there is no link between them.
Definition of Yoga in Panchang
The sum of the nirayana longitudes of the sun and the moon is divided into 27 equal divisions called yogas.
If the sum of the longitudes of the sun and moon in degrees exceeds 360 degrees, the subtract 360 degrees from the sum, convert into minutes and then divide that figure by 800.
For example on August 21, 2018, at 5:30 AM (IST), the longitude of the sun is 336 degrees 23 minutes and the longitude of the moon is 262 degrees 10 minutes (both nirayana).
The sum of the longitudes of the sun and the moon is equal to 598 degrees and 33 minutes.
Since the sum exceeds 360 degrees subtracting this value we get 238 degrees and 33 minutes.
Converting into minutes we have 238 X 60 + 33 which is equal to 14.313 minutes.
Therefore the Yoga is 14313/800 which is 17,89125. This means that 17 yogas are completed and the current yoga is the 18th one Variyan.
The Name of 27 Yogas
Vishkumbha, Preeti, Ayushman, Saubhagya, Shobhana, Atiganda, Sukarma, Dhriti, Shoola, Ganda, Vriddhi, Dhruva, Vyaghata, Harshana, Vajra, Siddhi, Vyatipata, Variyana, Parigha, Shiva, Siddha, Sadhya, Shubha, Shukla, Brahma, Indra and Vaidhriti.
How is Yog Calculated?
The sum of the nirayana longitudes of the sun and the moon is converted into minutes and then divided by 800. The quotient represents the number of yogas completed and hence the current running yoga is obtained by adding 1 to the completed number of yogas.If the sum of the longitudes of the sun and moon in degrees exceeds 360 degrees, the subtract 360 degrees from the sum, convert into minutes and then divide that figure by 800.
For example on August 21, 2018, at 5:30 AM (IST), the longitude of the sun is 336 degrees 23 minutes and the longitude of the moon is 262 degrees 10 minutes (both nirayana).
The sum of the longitudes of the sun and the moon is equal to 598 degrees and 33 minutes.
Since the sum exceeds 360 degrees subtracting this value we get 238 degrees and 33 minutes.
Converting into minutes we have 238 X 60 + 33 which is equal to 14.313 minutes.
Therefore the Yoga is 14313/800 which is 17,89125. This means that 17 yogas are completed and the current yoga is the 18th one Variyan.
Importance of Yog in Panchang
Yogas are very important from the point of view of day to day rituals in temples and in selecting muhurtas.
Certain yogas like Vyatipata etc are considered highly
inauspicious by certain Hindu communities.
Just like the Nakshatras the time period of Yogas varies
from 15 hours to 27 hours.
If the sum is 360 degrees then it is called Vaidhrita Vyatipata.
When the sum of the longitudes extends to the end of Anuradha Nakshatra i.e., is the sum is 226 degrees and 40 minutes, this phenomenon is called sarpa mastaka vyatipata.
Source - a few notes taken from Encyclopedia of Hinduism Volume VIII IHRF page 22 - 23.
Different Types of Inauspicious Yogas
If the sum of the nirayana longitudes of the sun and the moon is 180 degrees, the phenomenon is called Lata Vyatipata.If the sum is 360 degrees then it is called Vaidhrita Vyatipata.
When the sum of the longitudes extends to the end of Anuradha Nakshatra i.e., is the sum is 226 degrees and 40 minutes, this phenomenon is called sarpa mastaka vyatipata.
Source - a few notes taken from Encyclopedia of Hinduism Volume VIII IHRF page 22 - 23.