President Barack Obama hosted astronauts and students at the South Lawn of the White House yesterday to promote science and technology careers at "Astronomy Night".

Obama was joined by budding young scientists who checked out a moon rock and took selfies with Nasa astronauts and other science celebrities.

Among those attending was 14-year-old Ahmed Mohamed, who was arrest last month when he brought a science project - a homemade clock - to his Dallas-area school that teachers mistook for a bomb.

Obama encouraged young people to continue their creative endeavors.

"Some of you might be on your way to Mars. America can do anything. We just gotta keep on encouraging every new generation to explore and invent and create and discover.

"We gotta keep encouraging some young kid in Brooklyn or a budding rocket scientist in Alabama or that young girl who's dreaming to become an astronaut. Because as long as young people like so many of you who are here tonight keep seeking answers to the great questions, America can do anything," he told the crowd.

Obama looked at the moon through a telescope brought from the National Air and Space Museum.