Vaikunta Ekadasi falls on 21st Dec,2015 (Margazhi Masam / Dhanurmasam). It is also known as Mukkoti Ekadasi. This festival is dedicated to Lord Vishnu. Most of the Vishnu temples celebrate this festival in a grand manner. People visit Vishnu temples on this day. There will be heavy rush in Tirumala to have darshan of Sri Venkateswara swamy.
Planetary importance: Planets ‘Sun and Mercury’ in Dhanus rasi (Sagittarius)
Pooja / Worship: Many people in South India do fasting on this day. People visit Vishnu temples and pray to god for his grace. People, who are unable to go to temples , can chant the mantras or slokas of Lord Vishnu like Vishnu Sahasranamam or Vishnu Ashtottaram and offer sincere prayers in their homes itself.
Some of the photos of Tirumala Temple are posted below:
Photo Courtesy Here