Balloons have fascinated young and old alike since the Chinese invented them during the Three Kingdoms period in the third century. The first manned "fire balloon" flights were accomplished in 18th century France. Commercial hot air balloons can be expensive, but you can make a balloon that will float really high without having to set anything on fire. Some suggest that the Chinese accidentally invented hot air balloons when they discovered their paper lanterns would float if the vent hole in the top was too small. You can experiment with this yourself to see if it could be true.
Open the trash bag and pull it through the air until it is puffed up. You could also blow air into it with a hairdryer set on low.
Close the opening, using the twist tie. Tape over the twist tie, making sure it is tight and secure. Cut off the excess bag end above the tape.
Take your balloon outside on a sunny day. You may want to tie a string on the end if you intend to keep it. The air inside the balloon will become warmer than the air outside because the black bag will absorb heat from the sun. Heated air is buoyant so your balloon will float.
Cover the top vent hole of your paper lantern by gluing on additional crepe paper.
Put a tea light candle in the cup hanging below the lantern and light it, making sure you are in an open place with no flammable materials.
After a few minutes the lantern should float.
You can make a bigger solar balloon by cutting two to four bags along the edges, then taping them together securely before following Steps 1 to 3. If you want to see how far your solar balloon can fly, attach a tag with your name and phone number or e-mail address printed on it. With any luck, when it comes to rest it will find a friendly person who will contact you and tell you where it landed.
Don't print your physical address on the tag if you experiment with distance. There is no guarantee that the person who finds your balloon will be nice. If you are holding your balloon with a string, watch out for overhead power lines to avoid electrocution. If you experiment with the paper lanterns, be very careful with the open flame of the tea light. Children should get help from an adult for this project.