The Air Force Band on Tuesday delivered a surprise for hundreds of spectators at the Smithsonian Air and Space Museum’s Udvar-Hazy Center: An outstanding flash mob performance of “Greensleeves/What Child is This” and “Carol of the Bells.” As you can see in the video below, the performance began with a single oboist playing “Greensleeves” beneath the Space Shuttle Discovery, in the James S. McDonnell Space Hanger. She was soon joined by a cellist, another oboist, a harpist, and before long, the performance swelled to dozens of musicians throughout the hanger. The performance moved over to the main section of the hanger…