america

U.S. President Obama walks with Japan's Emperor Akihito and his wife Empress Michiko past an honour guard with Japan and U.S. flags during an official arrival ceremony at the Imperial Palace in Tokyo...U.S. President Barack Obama walks with Japan's Emperor Akihito (3rd L) and his wife Empress Michiko (L) past an honour guard with Japan and U.S. flags during an official arrival ceremony at the Imperial Palace in Tokyo April 24, 2014. Obama will use a state visit to Japan on Thursday to try to reassure Asian allies of his commitment to ramping up U.S. engagement in the region, despite Chinese complaints that his real aim is to contain Beijing's rise. REUTERS/Jim Watson/Pool

Jim Watson/Reuters

US president Barack Obama with Japan’s emperor Akihito and empress Michiko pass an honour guard during an arrival ceremony at the Imperial Palace in Tokyo 

Largest Freefall Formation world record attempt in Arizona USA...epaselect epa04150210 222 skydivers from World Team attempt to break the world record for the Federation Aeronautique Internationale (FAI) Largest Sequential Freefall Formation attempt at Skydive Arizona in Eloy, Arizona, USA, 01 April, 2014.

Roy Dabner/EPA

222 skydivers from World Team attempt to break the world record for the Federation Aeronautique Internationale (FAI) Largest Sequential Freefall Formation attempt at Skydive Arizona in Eloy, Arizona, US on Monday. 

U.S. President Barack Obama waves as he leaves Rome's airport...U.S. President Barack Obama waves as he leaves Rome's airport March 28, 2014. REUTERS/Giampiero Sposito  (ITALY - Tags: POLITICS)

Giampiero Sposito/Reuters

U.S. President Barack Obama waves as he leaves Rome‘s airport. 

US First Lady Michelle Obama (C) perform...US First Lady Michelle Obama (C) performs "tai chi" with students from the Chengdu No7 High School in Chengdu in China's southwest Sichuan province on March 25, 2014. Michelle Obama arrived in China on March 20 with her mother and daughters to kick off a seven-day, three-city tour where she will focus on education and cultural exchange.   AFP PHOTO / Peter PARKSPETER PARKS/AFP/Getty Images

Peter Parks/AFP

US First Lady Michelle Obama performs t’ai chi with students from the Chengdu No 7 High School in Chengdu, in China’s southwest Sichuan province. Michelle Obama arrived in China last week with her mother and daughters to start a seven-day, three-city tour where she will focus on education and cultural exchange. 

This image provided by NASA March 16, 2014 shows a portion of the Florida Keys taken by Astronaut Rick Mastracchio from the International Space Station. (AP Photo/NASA, Rich Mastracchio)

Rich Mastracchio/Nasa/AP

This image provided by NASA shows a portion of the Florida Keys taken by Astronaut Rick Mastracchio from the International Space Station 

A worker power washes the West Wing of t...A worker power washes the West Wing of the White House January 15, 2014 in Washington, DC. AFP PHOTO/Brendan SMIALOWSKIBRENDAN SMIALOWSKI/AFP/Getty Images

Brendan Smialowski/AFP

A worker power-washes the West Wing of the White House in Washington D.C

The tower of New York's World Trade Center rises through a blanket of fog on Wednesday morning, Jan. 15, 2014, in this view looking south from the 48th floor at 42nd St. and 11th Ave in Midtown Manhattan. New Jersey is visible at top right.

Girish Tewani/AP

The tower of New York’s One World Trade Center pierces a blanket of fog. This photo is taken looking south from the 48th floor at 42nd Street and 11th Avenue in Midtown Manhattan. 

Travelling White House staff and press board the rear steps of Air Force One on a foggy morning in Seattle...Travelling White House staff and press board the rear steps of Air Force One on a foggy morning in Seattle, November 25, 2013. U.S. President Barack Obama is attending fundraisers and events on the economy and immigration in Los Angeles and San Francisco on Monday.

Jason Reed/Reuters

White House staff and press board the rear steps of Air Force One on a foggy morning in Seattle. US president Barack Obama is attending fundraisers and events on the economy and immigration in Los Angeles and San Francisco on Monday. 

An aerial view at night of the downtown Chicago skyline. An Arctic air mass is expected to chill much of the Central Plains and the East Coast through Monday with wind-chill temperatures dropping into the single digits overnight in some places.

Kiichiro Sato/AP

A nightime aerial view of downtown in the US city of Chicago

Artists A.Signl, left, and B.Shanti, second from right, of the artist group Captain Borderline paint their mural   'Surveillance of the fittest' at a wall in Cologne, Germany, Thursday, Oct. 24, 2013. The painting shows an American Bald Eagle with surveillance cameras watching a herd of sheep to draw attention to the spying program of the American National Security Agency. Germany demanded answers to ìall open questionsî about U.S. surveillance Thursday following allegations that American intelligence may have targeted Chancellor Angela Merkelís cellphone, and her chief of staff noted that Washington hasnít denied past snooping.

Frank Augstein/AP

Artists A Signl (left) and B Shanti (second from right), of the artist group Captain Borderline, paint a mural “Surveillance of the Fittest” on a wall in Cologne, Germany, to draw attention to the spying programme of the US intelligence services