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.
The 27 yogas are 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.
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.