In the first day of the class, I saw a picture from Taiwan, where I am from. This is one of the festivals we have in Chinese culture, its called "Tian Deng", which means lanterns in the sky. The principle is similar to hot air balloon. You light up a fire in the bottom center of the sky lantern. And in the physics, we learned that hot air goes up due to its own big volume and low density. Thus, the hot air will fill up the lantern and go all the way up. 

You may be curious about the reason why we Chinese do this. Well, it is because people believe that the wishes you wrote on the lantern will be seen by Gods and eventually come true. People nowadays gather to a specific place in Taiwan and light up the sky lanterns together. When all the lanterns go up to the sky at the same time, it creates the beautiful view in the picture attached. As they go up higher, they become smaller, and they look like the stars in the sky. The view is incredible and definitely recommended if you ever visit Taiwan in February or October since that is the time of the festival.