A plane run on solar power took off on Friday for its first leg of a 19-hour trip from Moffett Field near San Francisco, Calif. to Phoenix Sky Harbor's International Airport.
Called "Solar Impulse," the plane is pretty slow, averaging a cruising speed of 43 miles per hour.
But the plane is noteworthy in other ways. It weighs 3,500 pounds and is able to fly without any fuel. It relies on energy from the sun which it collects from 12,000 photovoltaic cells on top of the wings.
The wings are also quite large, as they are as long as a commercial 747 jetliner's wings.
Only one person can be on the plane at a time, and this flight is manned by solar innovator Bernard Piccard.
Piccard and co-pilot Brian Jones made history in 1999 when they became the first people to fly around the world nonstop in a hot air balloon. He said he was shocked by the 8,100 pounds of propane used for that journey, prompting him to think of a greener way to travel.
While the plane is set to arrive in Phoenix tomorrow, the plan is to have the plane cross America and arrive at JFK in New York. It could take up to two months for the plane to make that journey, and the crew will stop flying it when weather conditions are bad.
After Phoenix, the plane will fly to Dallas, from Dallas it will go to St. Louis and from there it will go to Washington. Finally it will go from Washington to New York.
Piloting duties will be shared between Piccard and Andre Borschberg, co-founder of Solar Impulse.