It was right after the Siddhi day in November 1926, Sri Aurobindo retired from daily contact with his disciples and made the Mother in charge of their care and the Ashram. Thereafter he saw them only a few times in a year on what came to be known as Darshan days in the Ashram. The Sanskrit word "Darshan" means "seeing" and refers, in this context, to seeing Sri Aurobindo and the Mother and to receive their blessings.
At first there were three Darshan days: the Mother's birthday, Sri Aurobindo's birthday, and the Siddhi day. In 1939 a fourth day was added: the Mother's final arrival in Pondicherry. On these occasions, Sri Aurobindo and the Mother sat together in a small room, while the sadhaks and devotees approached one by one and offered flowers and bowed down at their feet for their blessings.
After Sri Aurobindo left his body in 1950, the Mother continued to give Darshan on these days. From 1963 onwards, she gave Darshan from the balcony and the terrace for five or ten minutes as she gazed upon those who had gathered in the street below.
During Sri Aurobindo's lifetime, messages were given out only occasionally on the Darshan days; afterwards, they were issued regularly. Some of these were written exclusively for the occasion, others were passages chosen from the works of the Mother and Sri Aurobindo.
That tradition still continues today. The day starts with a meditation around the Samadhi and also in the Ashram School courtyard. During the day, sadhaks , devotees and disciples are allowed to visit either Sri Aurobindo's or the Mother's room, depending on the occasion. Message cards containing passages from their works are distributed to all who attend the Darshan.
21 February: The Mother's birthday
29 February: The Supramental Manifestation day
24 April: The Mother's final arrival in Pondicherry
15 August: Sri Aurobindo's birthday
17 November: The Mother's Mahasamadhi day
24 November: Siddhi day also known as the day of realization. (Sri Aurobindo experiences the descent of Krishna into his body. He explains, "The descent of Krishna would mean the descent of the Overmind Godhead preparing, though not itself actually bringing, the descent of Supermind and Ananda.")
05 December: Sri Aurobindo's Mahasamadhi day
More details about Sri Aurobindo Ashram in Pondicherry