Holi or Holika, is a spring festival celebrated at the onset of the spring season, on the full moon day (Purnima) in the month of Phalguna. It is also the first day of the Hindu calendar (samvat) and a day of great joy and gaiety in the cities of Vrindavan and Mathura. Holi means the triumph of good over evil and conquest of sensual values by spiritual values.
Maha Shivratri (February 19th 2012) is celebrated in honor of Lord Shiva on the 13th (or 14th) night of the Krishna paksha (dark half or waning phase) of the moon (night before Amavasya) in the month of Phalgun (Feb-March) by almost all sects within Hinduism. It is a day of fasting for all devotees of Lord Shiva and is one of the eight most significant days of fasting in the Hindu Calendar.
The biggest celebration for Hindus, the festival of lights (Diwali or Deepavali), is celebrated on the amavasya night of the month of Ashvin (usually in late October or early November). The festival, which celebrates among many things, the return of Lord Rama (of the Ramayana) to his native land of Ayodhya after completing fourteen years of stay in the forest with his wife Sita and brother Lakshmana.
The second day of the Diwali festival, is the fourteenth day of the dark fortnight of the month of Ashvin, and is called Narak-Chaturdashi or Kali Chaudas and also known as Chhoti (-small) Diwali. This day is dedicated to the victory of Lord Krishna over the wicked demon king Narakasur.
Narkasur had fought against neighbouring kings and imprisoned 16,000 women, daughters of the Gods and saints. He had also defeated Lord Indra and taken away the magnificient kundale (earrings) from the ears of Aditi, mother of the Gods. When Lord Krishna learnt about Narakasur’s deeds, he decided to engage him in battle and liberate all the celestials.
Dhanteras is celebrated on the thirteenth day (teras) of the Krishna paksha (the waning cycle) of the lunar month of Ashwin in the Hindu calendar. It heralds the beginning of the five days of Diwali, the biggest festival for Hindus in India and all over the world.