Tahrir Square in Cairo became the hub for Egypt's revolution. Protesters are seen here rallying in the square on 11 February, the day they unseated President Hosni Mubarak - the country's ruler for nearly 30 years.

This picture taken on 12 March shows unimaginable devastation in Natori, Japan, after tsunami waves inundated the coast. The Magnitude 9 undersea quake on 11 March unleashed waves tens of metres in height, bringing death and destruction to the country's eastern seaboard.

Shipping containers lie strewn like Lego bricks across a dockyard in Sendai port, eastern Japan, following the 11 March earthquake and tsunami. The quake is thought to have moved Japan's main island about 20m westward.

This image shows the Fukushima Daiichi nuclear power plant in Japan taken at 1104 local time, just three minutes after an explosion wrecked reactor number three. The chain of events sparked by a cooling system failure at the plant plunged Japan into a nuclear emergency.

Libyan military aircraft burn on an airstrip in Misrata at the start of military operations against Col Muammar Gaddafi's regime. The picture was taken by GeoEye's Ikonos satellite on 23 March 2011.

The image on the left shows wreckage from a US military helicopter used in the raid that killed Osama bin Laden on 2 May. The same wreckage can be seen inside the Al Qaeda leader's Abbottabad compound in the picture on the right, taken by GeoEye's Ikonos satellite.

Chile's Puyehue-Cordón Caulle volcano pumps ash thousands of metres into the atmosphere in this image acquired by Nasa's Terra satellite on 11 June.

Viewers on the International Space Station saw the space shuttle Atlantis returned to Earth for the last time on 21 July, looking like a comet streaking across the atmosphere. The remaining space shuttles are destined to become visitor attractions at museums across the US.