Solar Plane
Solar Plane

A solar-powered plane has safely landed in the U.S. Pacific Coast state of California after completing the riskiest leg of its journey around the world - a 56-hour flight over the Pacific Ocean.

The flight was dangerous because there were no emergency landing sites.

The Solar Impulse 2 landed shortly before midnight Saturday at Moffett Airfield in California's Silicon Valley.

Earlier in the day, the plane flew over San Francisco's Golden Gate Bridge to the delight of many spectators, but remained aloft until night time when winds decreased.

Pilot Bertrand Piccard said landing in Silicon Valley will help link the plane's journey around the world to the pioneering spirit of the area.

Solar Impulse 2 pilots Bertrand Piccard, left, and
Solar Impulse 2 pilots Bertrand Piccard, left, and Andre Borschberg speak with reporters after their solar-powered plane landed at Moffett field in Mountain View, Calif., April 23, 2016.

"Can you imagine crossing the golden Gate Bridge on a solar-powered plane, just like ships did in past centuries? But the plane doesn't make noise and doesn't pollute," said Piccard in a live video feed from the plane.

The plane also moves very slowly at 45 kilometers per hour, double that when the sun's rays are strongest.

Next: New York

Solar Impulse 2 will fly across the continental U.S. to New York before crossing the Atlantic Ocean to Europe or North Africa before arriving back in Abu Dhabi, where the flight originated in March 2015.

The carbon fiber single-seat Solar Impulse 2  has a 72-meter wingspan, which is longer than the wingspan of a Boeing 747, and weighs about as much as an automobile.  The 17,000 solar cells built into the wings harness the sun's energy and charge onboard batteries.

The project is the brainchild of Swiss aviator Piccard and fellow pilot Andre Borschberg, who are alternating each leg of the historic flight. The duo say they are aiming to demonstrate that alternative energy sources and new technologies can achieve what some consider impossible.

WATCH: Related video of solar plane