Chandan Purnima, also known as Chandan Jatra, is observed on the full moon day (Poornima) in the month of Baishakha or Vaishakh (April – May) in
. In 2016, the date of Chandan Purnima is May 21. It is one of the most auspicious days in the 42-day Chandan Yatra. The deities of the Puri Jagannath Temple and Five Pandavas are taken on a boat along the Narendra Pond during the yatra. Jagannath Temple
Chandan in Chandan Purnima refers to the sandal paste used to smear on the idols during the festival to keep it cool during the summer heat. Sandal paste is also mixed in the water in the Narendra Pond.
Chandan Purnima festival is also held in numerous other temples dedicated to Lord Jagannath in Orissa. It begins on the Akshaya Tritiya day. In some temples the festival concludes on the Chandan Purnima day. In some temples the festival continues for 21 or 42 day festival.
You can find more details about Chandan Yatra in this article.