Although people sometimes think of classical music as the opposite of pop music, it can still be very popular. Like all kinds of music, classical music can be in many different moods: happy, sad, scary, peaceful, thoughtful, simple etc. Mozart wrote his serenades and divertimentos to entertain people at parties. Classical pieces of music can be quite short, but they can also be very long, like a big, musical story. A symphony by Mahler or Shostakovich can last for nearly an hour, and an opera is a whole evening’s entertainment.