A flyby is when a spacecraft passes close to a planet, moon, or other object in space without landing on it or going into orbit around it. During a flyby, the spacecraft speeds past to take photographs, collect data, and study the object from a relatively close distance before continuing on its journey.

NASA's Voyager spacecraft performed flybys of Jupiter, Saturn, Uranus, and Neptune in the 1970s and 1980s, capturing our first close-up images of these distant worlds. A flyby might last only a few hours or days, but scientists can gather years' worth of information during that brief encounter. The spacecraft can use the planet's gravity like a slingshot to change direction or gain speed, a technique called a gravity assist.

The word also describes when an aircraft passes close overhead. Military jets might perform a flyby during an air show, roaring past the crowd at high speed. You might look up and say, “Did you see that flyby?” when a plane passes directly over your backyard.