A plane that is powered by sunlight and uses no fuel has begun its attempt to travel across the United States.
The aircraft, named the Solar Impulse, set off from San Francisco Bay this morning where it will head to Phoenix on a flight expected to take 15 to 20 hours.
The journey across the US from San Francisco to John F. Kennedy airport in New York will take two months, making stops in Dallas and Washington on the way.
Travelling at a speed of around 40 miles per hour, the Solar Impulse has the wingspan of a large passenger plane but weighs the same as an average family car.
It is powered by 12,000 photovoltaic cells which cover the planes wings, meaning it can fly day and night without fuel.
The aircraft is not a smooth ride for pilots though, with the lightweight frame meaning it is vulnerable to bad weather.
The project, which began in 2003, has been described by one of its creators as a "mythical step in Aviation."
Andre Borschberg predicted that a solar-powered trip around the world could take place within two years.
He said the plane would never replace fuel-powered commercial flights but its aim is to help boost recognition of clean-energy technologies.