The brainchild of the Swiss pilot and adventurer Bertrand Piccard, the Solar Impulse 2 airplane has finally—after 12 years of research, development, and testing—embarked upon its journey to circumnavigate the Earth using only solar power. The huge, lightweight airplane gathers energy from 17,000 solar cells covering the top of its wings, which span more than 200 feet. The solar cells power four small electric motors that will keep the plane flying day and night.

“Our object is to make this airplane a symbol…