A solar-powered airplane that can fly day and night without using a single drop of fuel embarked on an unprecedented flight across the United States today (May 3).

The solar-powered aircraft, named Solar Impulse, took off from Moffett Airfield near San Francisco, Calif., shortly after 9:00 a.m. EDT (6:00 a.m. PDT). The plane will now head south on the first 19-hour leg of its journey, and is expected to touch down at Phoenix's Sky Harbor International Airport on Saturday (May 4) at 4:00 a.m. EDT (1:00 a.m. PDT).