APOD 3.2 (NanoSail-D)

Take a look around you.  Measure out an area of about 10 feet by 10 feet (or for you metric users out there, about 3.16 meters by 3.16 meters).  See how large it is compared to you?  It is also the approximate size of the first solar sail spacecraft's main sail, which is its only form of thrust, and only gets that thrust from the power of sunlight itself.  No, it isn't solar powered like a Prius, it gets its energy just from the force of particles of light hitting the sail.  NASA is even currently trying to get people to submit photos of this marvel of engineering to help them monitor the craft's condition.