Tourists gather around one of the generators in the Nevada wing of the powerhouse of Boulder Dam (later Hoover Dam) to hear its operation explained. 1940

The view from New Jersey A man peers across the Hudson River into Manhattan from his perch on the George Washington Bridge on December 22, 1936

21 years ago, in 1993 Dick Smith and John Wallington made the first non-stop flight across Australia in a hot air balloon.

The Third Avenue elevated train rumbles across lower Manhattan in this undated photo. City Hall can be seen in the background

The headline of the newspaper the man in this May 18, 1940 photo reads 'Nazi Army Now 75 Miles From Paris. This picture shows the corner of Sixth Avenue and 40th Street in Manhattan

Workers dig in Delancy Street on New York's Lower East Side in this photo dated July 29, 1908

Richard Nixon, the 37th President of the United States, waves goodbye as he boards a helicopter at the White House on August 4, 1974,

This circa 1983-1988 photo shows 172 Norfolk Street, which is now the Angel Orensanz Foundation, in New York.

19 March 1932 Crowds cross the newly opened Sydney Harbour Bridge

ohn F. Kennedy Jr. salutes his father’s coffin along with the honor guard

On July 20, 1969, Neil Armstrong put his left foot on the rocky Moon. It was the first human footprint on the Moon

General Gouraud marching in Aleppo 13 September 1920

Raising the Flag on Iwo Jima Joe Rosenthal, 1945

The stirring image of the Hindenburg zeppelin going down in flames helped galvanize public opinion on the dangers of airships and end their era once and for all 1937

Neil Armstrong snapped this image of fellow astronaut Buzz Aldrin during the first human trip to land on the Moon. It became a testament to American innovation and dedication 1969