Burj Dubai, the world's tallest tower, is seen during the opening ceremony in Dubai January 4, 2010. Dubai opened the world's tallest structure on Monday, and a statement said it was 828 meters (2,717 ft) high. Dubai's ruler Sheikh Mohammed bin Rashid al-Maktoum renamed the tower Burj Khalifa after the president of the United Arab Emirates and the ruler of the neighboring emirate of Abu Dhabi. [Agencies]