Once every year — on the full-moon day of the Hindu month of Chaitra (April) at sunrise — Hanuman Jayanti is celebrated to commemorate the birth of Hanuman.
On Tuesdays in some cases, Saturdays, many people keep fast in honour of Hanuman and give special offerings to him. In times of trouble, it is a common faith among Hindus to chant the name of Hanuman or sing his hymn ("Hanuman Chalisa") and proclaim "Bajrangbali Ki Jai" — "victory to thy thunderbolt strength".
Hanuman Jayanthi is celebrated in Andhra Pradesh on the Dasami or tenth day during the Krishna Paksha (waning phase of the moon) of Vaishakha month in the Telugu traditional Hindu calendar.Also known as Hanumant Jayanti, it marks the end of 41-day Hanuman Deeksha which began on Chaitra Purnima. In 2009, the date of Hanuman Jayanthi in Andhra Pradesh is May 19.In Tamil Nadu, Hanuman Jayanti is observed during Margazhi month (December – January).
The Birth of Hanuman
The story of the birth of Hanuman goes thus: Vrihaspati had an attendant called Punjikasthala, who was cursed to assume the form of a female monkey — a curse that could only be nullified if she would give birth to an incarnation of Lord Shiva. Reborn as Anjana, she performed intense austerities to please Shiva, who finally granted her the boon that would cure her of the curse.
When Agni, the god of fire, gave Dasharath, the king of Ayodhya, a bowl of sacred dessert to share among his wives so they may have divine children, an eagle snatched a part of the pudding and dropped it where Anjana was meditating, and Pavana, the god of wind delivered the drop to her outstretched hands. After she took the divine dessert, she gave birth to Hanuman. Thus Lord Shiva incarnated as a monkey, and was born as Hanuman to Anjana, by the blessings of Pavana, who thus became Hanuman's godfather.