A sky lantern, also known as Kongming 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.
In Asia and elsewhere around the world, sky lanterns have been traditionally made for centuries, to be launched for play or as part of long-established festivities. The name "sky lantern" is a translation of the Chinese name tiān dēng (天燈, 天灯). Sky lanterns have also been referred to as sky candles or fire balloons, however the latter term is also used to refer to balloon munitions used during World War II.
In Mainland China and Taiwan, 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.
The general design is a thin paper shell, which may be from about 30 cm to a couple ofmetres 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.***
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, during the Warring States period. Traditionally, however, their invention is attributed to the sage and military strategist Zhuge Liang (181–234 CE) whose courtesy name 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 (孔明燈, 孔明灯, kǒngmíng dēng). (However, some claim that the name actually comes from the lantern's resemblance to the hat Kongming is traditionally shown to be wearing.)
Sky lanterns are a possible explanation for some UFO sightings through the years.
In ancient China, sky lanterns were strategically used in wars. However later on, non-military applications were employed as they became popular with children at festivals. These lanterns were subsequently incorporated into festivals like the Chinese Mid-Autumn and Lantern Festivals.
Pingxi District in New Taipei City of Taiwan holds an annual Lantern Festival in which sky lanterns are released into the night sky with people's wishes written on the lantern.