In this episode from Physics Girl, Dianna Cowern explains how space ships can use sunlight to travel the stars in the same way that boats use wind to move across the seas. While solar sail spacecraft design is a more ‘recent’ exploration (circa 1976), the concept dates back a few hundred years. From Planetary.org’s light sail project:

Solar sails use the sun’s energy as a method of propulsion—flight by light. Light is made of packets of energy called photons. While photons have no mass, a photon traveling as a packet of light has energy and momentum.

Solar sail spacecraft capture light momentum with large, lightweight mirrored surfaces—sails. As light reflects off a sail, most of its momentum is transferred, pushing on the sail. The resulting acceleration is small, but continuous. Unlike chemical rockets that provide short bursts of thrust, solar sails thrust continuously and can reach higher speeds over time.

Watch this next: Sunlight is way older than you think.

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