A look around the solar aircraft attempting a night flight
An experimental aircraft that draws its power from the Sun is making a round-the-clock test flight.
The aim is to assess whether the plane can fly in darkness, using solar cells on its wings to generate enough power to stay in the air for 24 hours.
The HB-SIA plane, which took off from Switzerland, has the weight of a family car but the wingspan of a big airliner.
Andre Borscherg, CEO and co-founder of the Solar Impulse project, talked the BBC's Roger Harrabin through some of the plane's features.