A hot air balloon is a relatively large vessel which allows for human flight. A large pouch of fabric is filled with air that is heated to cause it to lift. A basket beneath the balloon carries passengers and cargo, and the wind guides it through the air.
A modern hot air balloon is heated by a small propane heater mounted below a small opening to the balloon, but above the basket where passengers travel. As the air heats up, it becomes lighter than the air outside the balloon, causing the craft to rise up in the air. While direction cannot be controlled much in a normal hot air balloon, altitude can be managed by releasing hot air or changing the strength of the flame. For skilled ballooners, some steering can be accomplished simply by changing altitude into differing wind currents; the ability to read the wind is important for those who race balloons.
A hot air balloon can come in a wide range of sizes, depending on its purpose. Small cloud hoppers are intended for only one passenger, and may have a balloon with less than 30,000 cubic feet (9,144 cubic meters) of air space inside. In contrast, some enormous hot air balloons, intended for groups of over ten people, may have over 500,000 cubic feet (152,400 cubic meters) of air space within. An average craft, meant to hold two or three passengers and a pilot, has around 100,000 cubic feet (30,480 cubic meters) of space inside the balloon.
The first hot air balloon trip with a passenger was in November of 1783, manned by a scientist and a marquis. This makes the hot air balloon the oldest successfully implemented vessel for human flight. Originally, it was thought that smoke itself made the balloons rise, and so a smoky fire was used to fill it. The military applications of hot air balloons didn't take long to be noticed, and they were used for reconnaissance during the US Civil War, and widely used during World War I. Some are filled with pockets of lighter-than-air gas such as helium or hydrogen, and use heated air for additional lift. This type is known as a Rozier balloon.
A hot air balloon can be compared to an airship, which is essentially a balloon with a steering mechanism built in. Many airships do not rely on heated air for their buoyancy, however, but instead use a gas that is naturally lighter than air, such as hydrogen or helium. Airships are also known as zeppelins or dirigibles. Those built using the same principles as a hot air balloon, with the addition of a way to steer directionally, are often called hotships.
Since its comeback in the 1960s, traveling by hot air balloon has become an incredibly popular pastime in the United States and Europe. Because of the striking views and near silence of the rides, they are considered ideal for romantic outings. Over 3,000 licensed pilots operate in the United States alone, with more appearing every day.