A solar-powered airplane left California on Friday for the first leg of a planned cross-country trip that its co-pilot described as a "milestone" in aviation history.

The Solar Impulse — considered the world's most advanced sun-powered plane — left just after dawn. Its creators said the trip is the first attempt by a solar airplane capable of flying day and night without fuel to fly across America.

"All the big pioneers of the 20th century have tried to fly coast to coast across America," said co-pilot and one of the plane's founders, Swiss-born Bertrand Piccard. "So now today we're trying to do this, but on solar power with no fuel with the first airplane that is able to fly day and night just on solar power."

The plane is powered by about 12,000 photovoltaic cells that cover massive wings and charge its batteries.

The delicate, single-seat Solar Impulse flies around 40 mph (64 kph) and can't go through clouds. It weighs about as much as a car, making it vulnerable to bad weather.

It plans to land in Phoenix, Dallas-Fort Worth, St. Louis, Washington and New York City. Each flight leg will take about 19 to 25 hours, with 10-day stops in each city.

Its creators said solar planes will never replace fuel-powered commercial flights. But the goal is to showcase the potential of solar power.

"What we look for is to have a new milestone in this very exciting history of aviation that can attract interest of the people, of the political world, of the media and show that with renewable energies and clean technology for energy efficiency, we can achieve impossible things," Piccard said.

The plane has previously impressed audiences in Europe.