Maasa-viseshams consist of four types viz, based on week days,
thithhis, asterisks and specified days in a month.
Week days: Certain week days are believed to be important for some deities and , worshipping on those days is considered as auspicious. ie Monday for Siva; Tuesday, Friday and Sunday for Bhagavathi (Durga, Bhadrakaali etc.); Friday for Ganapathi and Subramanya; Wednesday and Saturday for Saastha and Thursday for Vishnu and Hanuman and Sunday for Soorya (Sun).
Thithhis: Ekaadasi, Dwaadasi for Maha Vishnu, Thrayodasi and Ahstami for Siva, Chathurthhi for Ganapathi, Shashti for Subramanya, Pournami for Bhagavathi.
Asterisks: Aswathi, Bharani, Kaarthika, Makam, Pooram for Devi; Rohini for Krishna, Thiruvaathira for Siva and Parvathi, Punartham for Sree Rama, Kaarthika and Pooyam for Subramanya, Aayilyam for Naagas, Uthram for Saastha, Thiruvonam for Vishnu etc.
Specified days: First and last day (samkramam) of a Malayalam month besides first or ultimate week days of Monday, Tuesday and Friday of a Malayalam month for all deities.
