UPDATED: Day of Aashuura'

Update: It was announced before that the day of Ashura would be on Monday, Dec. 5 but this date was changed recently in an official statement issued by the Supreme Court in the Kingdom in Saudi Arabia.
 
In their official statement, they have announced that the Day of Ashura (10th of Muharram will fall on Tuesday, December 6, 2011, and therefore the 9th day will be on Monday, December 5. This is because the moon was not sighted on the 29th of Dhul-Hijjah so the month of Dhul-Hijjah should be completed 30 days.
 
Fasting is highly recommended on this day as well as one day before. More information on the Day of Aashuura'