Bart's Weather Balloon, also known as the "Hi! I'm Big Butt Skinner!" Weather Balloon and the "Buttzilla" Weather Balloon, was a school-owned weather balloon created for the school's Science Week that was sabotaged by Bart Simpson by placing folds that unfold at the pull of a string upon launch to give the illusion of Principal Skinner bending down and having an enormous butt sticking out of his pants, with him holding a sign. Bart attempted to hasten the launch of the balloon on the final day of Science Week by cheering loudly for Science. As soon as it lifted off, however, Bart pulled the string to reveal the modifications he made to the balloon, to the children's amusement and to Skinner's horror. He attempted to get it down itself, and then had the children throw rocks at it (promising that he will allow the child who successfully brings it down to not have to learn fractions), but missed and ended up hitting Skinner's car. Groundskeeper Willie then attempts to shoot it down with a shotgun, but missed and ended up inadvertently getting two fighter jets to shoot each other down. Because of this, Skinner punishes Bart by having him help him with his astronomy project of finding a new cosmic object for Skinner to name. Coincidentally, the balloon returned in the middle of the project, causing Skinner to grab the balloon from the climbing castle. However, the shock and horror that Bart ended up stealing his chance at getting a new cosmic body named caused him to release the balloon. The balloon was eventually destroyed when Bart's Comet, when burning up in the toxic portion of Springfield's atmosphere, rammed into it, causing it to also destroy Flander's fallout shelter.