A sky lantern (), also known as Kǒngmíng lantern (), or Chinese lantern, is a small hot air balloon made of paper, with an opening at the bottom where a small fire is suspended.
Sky lanterns have been made for centuries in cultures around the world, to be launched for play or as part of long-established festivities. The name sky lantern is a translation of the Chinese name but they have also been referred to as sky candles or fire balloons.
Several fires have been attributed to sky lanterns, with at least one 21st-century death caused. Sky lanterns have been made illegal in several countries such as Vietnam which has banned the production, sale, and release of sky lanterns throughout the country since 2009. Many areas of Asia do not permit sky lanterns because of widespread fire hazards as well as danger to livestock.
Construction
The general design is a thin paper shell, which may be from about 30 cm to a couple of metres across, with an opening at the bottom. The opening is usually about 10 to 30 cm wide (even for the largest shells), and is surrounded by a stiff collar that serves to suspend the flame source and to keep it away from the walls.
When lit, the flame heats the air inside the lantern, thus lowering its density and causing the lantern to rise into the air. The sky lantern is only airborne for as long as the flame stays alight, after which the lantern sinks back to the ground.
In China, Taiwan and Thailand, sky lanterns are traditionally made from oiled rice paper on a bamboo frame. The source of hot air may be a small candle or fuel cell composed of a waxy flammable material.
In Brazil and Mexico sky lanterns were traditionally made of several patches of thin translucent paper (locally called "silk paper"), in various bright colors, glued together to make a multicolored polyhedral shell. A design that was fairly common was two pyramids joined by the base (a bipyramid, such as the octahedron) sometimes with a cube or prism inserted in the middle. Only the smaller models had a full frame made of bamboo or thin wire; the slight overpressure of the hot air was sufficient to keep the larger ones inflated, and the frame was reduced to a wire loop around the bottom opening. The "candle" was usually a packet of paraffin or rosin tightly wrapped in cloth and bound with wire.
History
China is considered to have developed the first simple hot-air balloons. According to the sinologist and historian of science Joseph Needham, the Chinese experimented with small hot air balloons for signaling from as early as the 3rd century BC. Their invention is, however, traditionally attributed to the sage and military strategist Zhuge Liang (181–234 AD), whose reverent term of address was Kongming. He is said to have used a message written on a sky lantern to summon help on an occasion when he was surrounded by enemy troops. For this reason, they are still known in China as Kongming lanterns (, , kǒngmíng dēng).
Another suggested origin is that the name actually comes from the lantern's resemblance to the hat Kongming is traditionally shown to be wearing.The Mongolian army studied Kongming lanterns from China and used them in the Battle of Legnica during the Mongol invasion of Poland. This is the first time ballooning was known in the western world.
In the history of military ballooning, the lanterns were also used for military signals, In the history of ballooning, these became the first hot air balloons used in the West, in Europe, during the Mongol Invasion of Poland. Sky lanterns could be a possible explanation for some UFO sightings through the years.