WASHINGTON: The United States will today mark the 40th anniversary of its conquest of the moon, a triumph of scientific endeavour now remembered at a time when US dominance in space is increasingly uncertain.

President Barack Obama kicks off a week of events today when he meets at the White House with the crew of the Apollo 11 mission, who became the first to accomplish the dream of ages and walk on the surface of the moon.

"That's one small step for man, one giant leap for mankind," said astronaut Neil Armstrong as he stepped down from the lunar lander on July 20, 1969, as an estimated 500 million people on Earth crowded around televisions and radios.