Alexanderson Day is a special day that celebrates the achievements of a man named Ernst F.W. Alexanderson. He was a very smart person who made important inventions that help people communicate over long distances using radio waves.
Radio waves are like invisible waves that travel through the air and can be picked up by special devices called radios. Alexanderson made a special kind of radio called the Alexanderson alternator, which was used to send messages over really long distances, even across oceans!
On Alexanderson Day, people remember how important his inventions were and how they changed the world. This day is a way to honor and celebrate all of the things that Alexanderson did to help make the world a better and more connected place.