Hey Arnold!

Olga Comes Home / Sally's Comet (1x15)

Air date: Nov 25, 1996

First Part: Jealous about her smart, talented, popular older sister Olga returning home from college, Helga fiendishly changes one of her grades from an A to B+, which sends Olga into a deep depression. Second Part: Arnold and Gerald must turn off all the lights in the city if they want to see Sally's Comet.